Heat and AC issues?

[John 04 2670]

Well, this was perplexing in my 04 2670 -

While camping last week I went to turn on the heat, and the blower seemed to be racing at a much higher speed and very loudly. I couldn't even hear it ignite but it must have as I felt it a diminished amount of heat coming out of it and the exhaust seemed to be less flow than normal.

A couple of days later I turned on the AC it cooled it down nicely but when it got below the setting on the thermostat the fan would shut down but the compressor would run on it's low.

I'm thinking thermostat or AC control board?

Thoughts?

[JohnB]

Hi John,

Your issues are going to take some digging to sort out. There "might" be a common issue affecting both the furnace and the AC unit, OR they can be separate issues just happening at the same time.

Let's start with what might be a common issue and then rule that in or out. Would you happen to have a volt meter? And know how to use it?

Another question: What brand and model power converter do you have? If your 2004 T2670 still has the original power converter, it would be an American Enterprises power converter. But the model can be one of two as American upgraded the model over that time frame. The early builds, which were made in the year 2003, could have the CS-6000, the later build dates, very late Dec. 03 up to mid-2004, could be a CS-6000XL.

Which do you have? Or, had as some of those power converters went bad and were replaced by other club members, myself included.

A possible common issue for the furnace and the AC unit control is the 12-volt DC power. If the voltage is very high, it can affect the AC control board and may mess with the furnace motor. Could you do this test if you can and report back the findings?

1. Start with the camper unplugged from shore power. Turn the battery disconnect off.
We want the battery at rest with no surface charge left on it. Let the battery be off for 6 hours or more. Overnight is fine. If it has already been unplugged for that long, then could you do this test?
2. At the battery terminal, check the battery voltage. If you have a digital meter, you need the voltage read out to at least one decimal point. What is the voltage? 12.7 VDC is 100% state of charge. It may not be that high, but what is it?

3. Plug the camper into shore power. This will power up the power converter.
4. Turn the battery disconnect on. With the voltmeter, check the voltage at the battery terminals. What is the voltage? The American converter would be either in the range of 13.25 volts DC or 13.6 volts DC when it was working correctly.

5. Let the camper be powered up for several hours, 4 to 6 hours or more. Mark how many hours went by, then check the battery voltage again. What is this voltage?

We are looking for the proper battery voltage with loads, then with the power converter being on, and then over time with the power converter being on.

High voltage above 14.4 volts or higher non-stop for days on end is bad. It will cook out the battery, and 15 volts and up is the start of other issues.

If the battery and power converter test out OK, we can then start digging into the furnace and the AC unit. We want to ensure we are not over-volting the AC or furnace before starting into them. And, are you electrically friendly when dealing 12 VDC and 120 VAC power? We would be getting into electrical troubleshooting, and I do not want to go there if this is more than you are comfortable with.

Hope this helps

John

[John 04 2670]

Thanks for your response. I do have a volt meter and have no problems using it.

I will add my response here:

Another question: What brand and model power converter do you have? If your 2004 T2670 still has the original power converter, it would be an American Enterprises power converter. But the model can be one of two as American upgraded the model over that time frame. The early builds, which were made in the year 2003, could have the CS-6000, the later build dates, very late Dec. 03 up to mid-2004, could be a CS-6000XL.

Which do you have? Or, had as some of those power converters went bad and were replaced by other club members, myself included.

JRH - I just installed a brand new WFCO inverter/converter WF-8955 55 amp.

2. At the battery terminal, check the battery voltage. If you have a digital meter, you need the voltage read out to at least one decimal point. What is the voltage? 12.7 VDC is 100% state of charge. It may not be that high, but what is it?

JRH - It is 12.7.

3. Plug the camper into shore power. This will power up the power converter.

4. Turn the battery disconnect on. With the voltmeter, check the voltage at the battery terminals. What is the voltage? The American converter would be either in the range of 13.25 volts DC or 13.6 volts DC when it was working correctly.

JRH - It's reading 13.6 plugged in.

5. Let the camper be powered up for several hours, 4 to 6 hours or more. Mark how many hours went by, then check the battery voltage again. What is this voltage?

JRH - It's still reading 13.6 volts, 4 hours later.

Also, I did some other research and pulled the yellow (AC) wire off the thermostat, the compressor still comes on instantly when I power up the circuit even with the yellow wire pulled. This would seem to tell me it is an issue at the A/C unit, probably the control board I'm thinking?

[JohnB]

Originally Posted by John 04 2670

Thanks for your response. I do have a volt meter and have no problems using it.

snip...

I will add my response here:

JRH - I just installed a brand new WFCO inverter/converter WF-8955 55 amp.

2. At the battery terminal, check the battery voltage. If you have a digital meter, you need the voltage read out to at least one decimal point. What is the voltage? 12.7 VDC is 100% state of charge. It may not be that high, but what is it?

JRH - It is 12.7.

3. Plug the camper into shore power. This will power up the power converter.

4. Turn the battery disconnect on. With the voltmeter, check the voltage at the battery terminals. What is the voltage? The American converter would be either in the range of 13.25 volts DC or 13.6 volts DC when it was working correctly.

JRH - It's reading 13.6 plugged in.

5. Let the camper be powered up for several hours, 4 to 6 hours or more. Mark how many hours went by, then check the battery voltage again. What is this voltage?

JRH - It's still reading 13.6 volts, 4 hours later.

Also, I did some other research and pulled the yellow (AC) wire off the thermostat, the compressor still comes on instantly when I power up the circuit even with the yellow wire pulled. This would seem to tell me it is an issue at the A/C unit, probably the control board I'm thinking?

Hi John,

You have done well; the power converter and the battery are doing well. At this point, we can put the power input off to the side as a problem.

To what I highlighted in blue, let's clarify that statement a little more before we declare the AC control board bad, it might be, or there is another issue.

Yes, the yellow wire is the cool control wire at the T stat. Let's also confirm if you are on the same older Dometic analog T stat or if you did an upgrade; many of us have, as they do not regulate very well. Is this the T stat you are using, OR did you upgrade, and if so, what brand model?

The Dometic analog T stat looks like this with the cover-off.




The wiring diagram for the T stat


When you said the

the compressor still comes on instantly when I power up the circuit even with the yellow wire pulled

OK the yellow wire is pulled, hold that thought.

1. Which power came on, the 12 VDC or the 120 VAC?

2. Did the fan come on with the compressor?

3. Is the fan control switch in the "on" or "Auto" positions?

The Dometic older analog T stat control is what we call, a "sink" type of control. The yellow wire is looking for DC (neg -) ground to create a run signal. The wire floats until it is grounded, and then the control board up in the ceiling gets the signal to go into cooling mode. This is not a "sourcing" control looking for positive DC power to get a run signal. NOTE: The defrost cycle will override the fan shut down when in auto mode; when the T stat is satisfied, the compressor will shut down, and the fan keep running if the defrost mode is activated.

But the yellow wire is for all of the cooling mode. The compressor and fan get the same signal to run simultaneously. When the fan switch is in auto, the fan cycles on and off with the compressor. If the fan is in the "on" position, then the fan runs all the time, regardless of the compressor. It is used just to circulate air in the camper.

So, if the fan ran with the compressor when you powered up the circuit with the yellow wire off, we might have a wiring issue with the yellow wire. All that yellow wire needs is a path to the ground, and it's a run signal even with no T stat in the equation. A skinned wire touching metal would do it. But the fan would run also.

If there was no fan at all, no yellow wire on, you powered up, and only the compressor runs, that then points to the AC PC board being bad; either the onboard relay burnt on or the control logic components burnt and is turning on the relay.

Let me know what power turned on and what the fan did or didn't do while I search for where I bought my last AC control board. I just bought one a few months ago. It is not a hard thing to change.

Hope this helps,

John

[John 04 2670]

Thanks so much for digging deeper John.

So I am still running the original thermostat. Never had any problems with it.

I will try to clarify about my situation.

Basically, if the camper is plugged in, the AC compressor is always on, even when the fan is on "auto" and the system is "off". In this case the fan will not be on.

If I turn the fan to "on" the compressor and fan will run and the camper will cool way down.

If I turn the system to auto and set the thermostat lower than the interior temperature, the compressor will be on and the fan will be on until it gets to the set point temperature at which point the fan will turn off but the a/c compressor will continue on indefinitely.

Since I obviously don't want the compressor to run indefinitely I have been throwing the 110v breaker for the air conditioning which turns off the compressor and fan.

So to test the thermostat, I had the 110v breaker off to the a/c, I then pulled the yellow wire off the thermostat, had the system to "off" and the fan to "auto", then turned on the 110v breaker to on the a/c and the compressor started but no fan.

[JohnB]

Hi John,

OK, got it now. From the below info, this points to the AC compressor relay on the control board is welded closed and on. ( They are normally open contacts) In this case, the only thing that will turn it off is the 120 V AC breaker.

Originally Posted by John 04 2670

Since I obviously don't want the compressor to run indefinitely I have been throwing the 110v breaker for the air conditioning which turns off the compressor and fan.

So to test the thermostat, I had the 110v breaker off to the a/c, I then pulled the yellow wire off the thermostat, had the system to "off" and the fan to "auto", then turned on the 110v breaker to on the a/c and the compressor started but no fan.

I'm doing some digging right now for the parts, stay tuned, will be back shortly.

John

[JohnB]

Hi John,

This "should be" the Dometic analog control box in your camper. Check this part number before you buy the control board I will list below. This control box is now discontinued as a complete part assembly: the box, the covers, the control board inside, the white roof unit receptacles, etc. But, I can find the control board for sale. So we just changed the control board and reused the old box.

Take the ceiling grill off where the mesh filter is: Your 2004 plastic ceiling surround may be different than this pic; this is from a 2007 Sunline. See the silver control box.


The part number is on the sticker to the left, you have to take the whole box out to see the full sticker.


With all the power off, 120 VAC and 12 VDC, take the two screws that hold the control box to the metal ceiling plate, and the entire box will come out. Wiggle it out. There are wires all over; You can unplug the white connector on the black cable that comes down from the roof unit to give some working room. All the wire nutted wires from the T stat can be left on. The 120 VAC Romex can be left on, too. We will only be unplugging the PC board.


In this pic, I had the white ceiling shroud off as I removed the roof unit; you can leave yours still on. The control box will still come out with that shroud on.


Unscrew the cover, and it exposes the control board inside.


To remove the PC board, first I suggest you take a pic of yours so you know where all the wire colors plug back onto. Unplug all the wires.

I do not have the exact pic, but there are 4 white plastic posts that hold the PC board to the metal case. Two on the bottom and two in the top in these pics.


Here is the new board installed, it is green, whereas the old one was a white PC board but you can see the 4 white plastic posts. A different manufacturer of the board.


The white posts have a small white tang that pops out once the board pushes through and holds the PC board in. Using needle nose pliers, gently squeeze the tang on the post and hold it squeezed. With your other hand, gently lift that corner of the PC board just a bit. Let go of the needle nose, and the PC board hole will hold the tang closed. Do the other three; the board will come up and out of the metal box with the four posts still in the box. Insert the new board on the four posts, and it will slide right over the tangs, and click in. Then, put the rest back together.

Be careful with those plastic posts; they are fragile. I am still determining where to buy a new one if they break.

Here is where I bought the last few boards: (yes, I have replaced several of these in different campers)
Dometic 3106996.022 Heat Cool Analog Control Relay Board Kit

Here are Boat & RV accessories here in Ohio.
https://www.boatandrvaccessories.com...39911731724438

Heads up, many no-name brands of these boards are out there claiming to be the ones; watch the wording; you want the ones that say Domeitc is the manufacturer. Not the ones that state they comply with the Dometic part and are a no-name manufacturer. I wanted to avoid risking it and paid some more to get what I believed was a better-quality board. Amazon is loaded with clones of these. Scroll down and look at the name of the manufacturer.

This should get you back going again, at least on the AC unit.

Next, we need to start on the furnace. Something is a muck there—more on Thursday on that.

Hope this helps

John

[John 04 2670]

Part ordered from your link, I really appreciate your help John!

[JohnB]

Originally Posted by John 04 2670

Well, this was perplexing in my 04 2670 -

While camping last week I went to turn on the heat, and the blower seemed to be racing at a much higher speed and very loudly. I couldn't even hear it ignite but it must have as I felt it a diminished amount of heat coming out of it and the exhaust seemed to be less flow than normal.

Thoughts?

Hi John,

First off, you are very welcome. Glad to help as I can. Let us know how the PC board changeout goes.

Now to the furnace. I have some "thoughts" on the problem since we are ruling out high DC voltage, at least for the moment.

Here are a few questions to get more background;

1. When you discovered the furnace blower running faster and with less air discharge, was this the first time you fired up the furnace this season?

2. About how long (days, months, or years) since the last time it worked correctly?

3. The furnace has two blower wheels, one to move inside air, drawing air through the inside air intake grate, and blowing out the heat ducts inside the camper. And a second blower wheel for outside air to draw fresh air into the heat exchanger and then blow out leftover gas fumes and heat outside the camper. Both blower wheels are mounted on a single double-ended long shaft motor. When you stated this,

I felt it a diminished amount of heat coming out of it, and the exhaust seemed to be less flow than normal.

Was the exhaust, the heat, and the flow on the inside heat ducts or the outside exhaust port? Or both?

4. Where was the camper stored over the last winter season? Could you describe the area and access to the outside world where it was stored?

5. Have you seen any evidence from critters inside the camper this spring? Mouse droppings, squirrel leftover nut parts, etc.

6. To help me understand your 2004 T-2670 (I have never been in that non-slide bunk house floor plan), where is the furnace located? From the floor plan layout, I assume a few locations.

A. Mounted under the sofa on the camper's left side (non-entry door side).

B. Mounted under the bunks on the left rear of the camper.

C. Mounted under the camper's fridge, range, or sink on the right side (entry door side).

Those answers will help get us to the next stage of figuring this out.

Thanks

John

[John 04 2670]

Thanks John, I will respond below each question:

1. When you discovered the furnace blower running faster and with less air discharge, was this the first time you fired up the furnace this season?

JRH - Im pretty sure I used it this spring and it worked fine in May. It certainly worked great in December when we used it

2. About how long (days, months, or years) since the last time it worked correctly?

4 months ago was the last time I used it and it worked fine then.


3. The furnace has two blower wheels, one to move inside air, drawing air through the inside air intake grate, and blowing out the heat ducts inside the camper. And a second blower wheel for outside air to draw fresh air into the heat exchanger and then blow out leftover gas fumes and heat outside the camper. Both blower wheels are mounted on a single double-ended long shaft motor. When you stated this,
Quote:
I felt it a diminished amount of heat coming out of it, and the exhaust seemed to be less flow than normal.
Was the exhaust, the heat, and the flow on the inside heat ducts or the outside exhaust port? Or both?

- The flow seemed to be less out of the vents and the exhaust. It did fire off but the exhaust was not as hot nor was the air in the vents.

4. Where was the camper stored over the last winter season? Could you describe the area and access to the outside world where it was stored?

- outside and covered

5. Have you seen any evidence from critters inside the camper this spring? Mouse droppings, squirrel leftover nut parts, etc.

- No evidence

6. To help me understand your 2004 T-2670 (I have never been in that non-slide bunk house floor plan), where is the furnace located? From the floor plan layout, I assume a few locations.

A. Mounted under the sofa on the camper's left side (non-entry door side).

- It is here, under couch, exhaust on the non-entry side

B. Mounted under the bunks on the left rear of the camper.

C. Mounted under the camper's fridge, range, or sink on the right side (entry door side).

[JohnB]

Hi John,

Now that we know some background on your furnace, I have a few thoughts on a direction to look for. Since it was only about four months when the furnace worked right, and you were very sure it worked last winter; this is pointing to an "event" that happened since the last time it worked OK.

Now, the furnace blower is at a higher-than-normal speed; inside the camper, the air coming out of the duct is less volume and less heat. This pattern of less air and less heat also follows outside on the furnace exhaust.

The faster furnace blower points to the problem: How can furnace blowers, inside and out, both have less flow and less heat coming out of their respective areas? I have yet to run into your problem in my line of camper work, but I know the inner workings of the furnace and the characteristics of squirrel cage blowers from my prior industrial work experience.

Here are the basics of a squirrel cage blower, which the Atwood furnace uses on the inside and outside fan blades. The power from the motor overcomes the spinning of the blower wheel mass and the amount of air it draws through it. The motor amperage goes up with the more air that is pumped through it. The less air going through, the less motor power is needed.

Now to the camper using that basic concept. Think of a home vacuum cleaner, an upright on the carpet, or a shop vac sucking up dirt or sawdust. Let's take the shop vac; it is easier to hear and see what I am talking about. On the shop vac, the blower is sucking through the hose with an attachment nozzle on the end of the hose often. The blower speed and sound are constant, with the vacuum just running and not sucking up anything. Now you start sucking up dirt/sawdust, and your hose attachment is close to sealed off as you press the end of the nozzle tight to the floor. While you feel suction, you are choking the nozzle almost totally off. There is little air from the vacuum exhaust, as very little air is allowed into the vacuum blower. You also hear the motor speed up and whine as it is not under an average volume load of moving air through the blower.

I "think" the same problem is happening with your furnace. Either the inside blower is choked, starving the inside blower, or the discharge of the inside blower is choked in the ducts, etc. The same goes for the outside blower; it can be choked on the air inlet, not allowing air into it or discharging. Since the blower motor is a double-ended shaft motor with two blades, either blower blade can affect the other, OR both blowers are choked simultaneously (less likely but possible).

If the blowers are not moving the right volume of air being choked, they cannot pump out enough heat from the heat exchanger, inside or out. And the blower motor would speed up with less load.

The blower has a sail switch to ensure enough air is moving through the system, not to allow the system to overheat if the blower is not running fast enough. Low voltage can cause the sail switch to not trip, and the gas burner will never fire off. The motor runs slower due to low voltage, and the sail switch safety keeps the gas system from starting or shutting it off if it is running. The sail switch only sees the inside blower volume, not the outside. If it works correctly, the sail switch sees enough air volume inside to let the system fire off the gas system. However, if the outside blower is choked, lower motor power draw is there, and thus, the motor can speed up as the air volume load is lower. Less air is moving through the inside of the heat exchanger, and even if the gas burner is on, the heat cannot get into the camper or out the exhaust port. The heat exchanger's gas burner area is getting very hot due to not being cooled properly with a low exhaust air volume.

Thinking through this, I recommend not using the furnace until this problem is resolved. You can overheat the gas burner end of the heat exchanger.

Now, how did this happen? You are going to have to hunt for the obstruction. But here are some places to look.

Here is the outside. These pics are from my bench test work on one of my camper restorations. This furnace has fewer BTUs than yours, but only the gas jet is smaller; everything else is the same.

Here is the outside cover of the furnace. I installed an insect screen on this, and I wonder if you have one. Does it?


Here is the cover off; remove the four screws, and the cover will come off. The foam gasket may be stuck, but it will come off with the four screws out.


Turn off the power to the camper, battery, and 120 VAC shore power. Shut the gas tanks off, too.

You now want to look at the left side of the gas valve for the outside exhaust blower air intake. You are looking for it to be blocked with something. Mud daubers or other insects like the smell of propane, and they can smell it on the exhaust and, with an insect screen, get in easily.

You can see the round hole in the silver metal cover to the left of the gas valve. You can remove the exhaust pipe if needed to get better access. There is a thumb screw that holds it from coming out. Loosen and wiggle the exhaust pipe and pull it out.


The thumb wing nut is shown here that holds the exhaust pipe in. You only have to loosen it; the exhaust pipe is slotted.


These pics I'll show so you can see the exhaust blower wheel. You may not have to pull the gas burner out, but this is what things look like with the burner out. Hopefully, your blower wheel is not plugged with insect stuff.






See if you can find anything choking that outside blower or stuck in the blower wheel.

If nothing is choked, we need to look inside the camper. And better to check even if you do find something outside.

Look at the left side of the furnace in this pic and on top of the furnace. The inside blower draws air into the inside blower blade past the PC control board and from the openings on top of the furnace. Outside, look at the control board area for something blocking this area.


If needed, you can unplug the white connector on the control board, loosen the wing nut, and pull the PC board out to get better access to the blower air intake.


Go inside, lift up the sofa, and look at the top of the furnace; look to the right where the wire plugs into the furnace where the air intake is, and on top, does something fall into that is choking the air intake?


Have a look and report back.

Heads up, when you screw the white cover back on, be cautious with those four screws. Do not over-tighten; you will tear out the threads on the black plastic flange. You can use the power screwdriver, but stop about 1/4" away, hand tighten, and just enough to compress the gasket and stop. You can see here the plastic round boss the screw goes in is cracked; yours may even be cracked from the original install.




If yours is beyond use, they do sell a replacement flange; it is just a different part number than stamped in your plastic.

Happy hunting.

John

[JohnB]

Hi John,

Thinking some more on this, if you take the exhaust pipe out and see a nest of a mess inside the heat exchanger, here are a few tips:

- When you remove the gas burner and valve, put painter's tape, masking tape, or even standard electrical tape over the gas line and the gas line fitting on the valve to keep any dirt out of the gas system. I would avoid duct tape, it is too sticky, and you have to go in with a chemical to get the adhesive stuck on off.

In this pic:


- The top port/hole is the air intake. It is OK to blow into that hole with compressed air, or better, the exhaust hose from a shop vac to blow out dirt inside the heat exchanger. The shop vac exhaust hose blowing may be better than compressed air as you need a large volume to get through the zig-zags of the heat exchanger.

- The bottom port is the air exhaust. Do "not" blow into that hole; the best is suction from the shop vac to get debris out from that port. You want to avoid driving much of anything into the heat exchanger, making it harder to get out.

As FYI, this is what the heat exchanger looks like. You should not have to get this deep, hopefully in the furnace. The white gasket that seals the heat exchanger to the furnace body is no longer available. The last gasket I bought was in the 2009/2010 time frame. Dometic, who bought out Atwood, is discontinuing parts left and right with low sales volume. A dealer may have bought out the last of the stock when they discontinued it; that is about the only way to get an OEM gasket. Point: If you have to get this deep, do not separate the heat exchanger from the sheet metal body.







I have had small hornet nests in the exhaust pipe, but never a mud dauber, etc, nest large enough to create a major blockage. Hope you are not the first to report one here on the forum.

Good luck,

John

[John 04 2670]

Thanks so much John, I took at look at the furnace a couple of nights ago and I do see "mud" in the blower wheel. I'm going to try to access it soon. I have had the burner out so I am familiar with that part at least. Also, the AC circuit board is getting close to delivery. I will try to make some forward progress soon and I'll keep you updated.

[JohnB]

Hi John

Originally Posted by John 04 2670

Snip..

"mud" in the blower wheel.

Oh boy, those darn buggers strike again. Actually, if they only muddied up the blower wheel, that is easier to clean up that mess than inside the heat exchanger.

If you can, take a pic of the mess and post.

I will hunt up the Camco screens I have been using with good success and post to help you prevent this from happening again.

Good luck with the blower clean out.

If needed you can pull the blower blade out to help clean it better. The plastic wheel hub sometimes gets stuck to the shaft. After you unloosen the shaft clamp and remove it, it will expose 3 slots in the wheel hub that go as deep all the way to the shaft. The clamp has a folded in tooth that fits in one of the slots so it will not spin. The clamp has to come straight off, can’t rotate it.

You can squirt some penetrating oil in the slots and very gently tweak with a small flat blade screw driver to gently open the slot just a little. Don’t overdo it or you can crack the hub. If you can’t get the wheel to budge, then leave it in and try your best to get all the mud out with it in. I have been able to dig the mud out of fridge gas burners tubes dry before, but maybe wet a little if needed to help loosen up the mud

John

[John 04 2670]

Well, the mud was just on the wheel. Removed the gas burner and valve, knocked the mud free in the wheel, and vacuumed the debris out. I guess when I started the furnace the mud broke up in the wheel and bounced around making the noise. I ran the furnace for a bit and everything worked great.

Installed the new board today, your comments about the little clips were a huge benefit, I would never have known how to release the board if I didn't know what I was looking for. Tested it out, everything worked normally. I really appreciate your help John!

[JohnB]

Hi John,

Great news!!! Good job. And you are welcome. Glad to help as I can.

Consider looking into these insect screens for the future to keep the bees, hornets, and mud daubers out of the furnace and other gas appliances. These will fit your vintage Sunline. I have used many of these stainless screens and they work well.

The links are to RVUpgrades.com. You do not have to get them here, but I shop with these folks often, and they often beat out many places. They do charge freight unless you can find up to $99 worth of items, then free freight. Many times, even paying the freight, they can still be cheaper and have given good service.

Furnace:
Camco 42142 RV Flying Insect And Pest Screen - 5" x 4-3/4"
https://www.rvupgradestore.com/Camco...-p/79-8003.htm

The Atwood water heater: Yes, the bugs get into these also.
Camco 42145 RV Flying Insect And Pest Screen - 6" x 8-1/2"
https://www.rvupgradestore.com/Camco...-p/79-8006.htm

The fridge: Yup, mud daubers and hornet nests are common.
Camco 42149 Insect And Pest Screen for Dometic Refrigerator Vent - 20" - 3 Pack
https://www.rvupgradestore.com/RV-Do...-p/07-0140.htm

Happy camping,

John