Yearly Issues with Hydroflame 8531-III

[RandyJ55]

Hello there;
Once again I'm having an issue with my new TDR clicking after 20 to 25 seconds. After verifying the integrity of the DSI board , I went through the connections and I suspect my sail switch. Is there a way to test the sail switch other than with a continuity test? I have a closed circuit on the loop coming from and going to the limit switch so I believe that the limit switch is fine.I was wondering in anyone had a wiring schematic for the hydroflame 8531-III or one of the series that would include that model. Every year that I have an issue with my furnace I find the answers here. I also have 2 blue wires coming from the inside of the rv , one to the breaker linked with a red wire and the other ,to the sail switch. does it make a difference which blue wire connect to which conponent? I have to sort out this issue because I installed a new burner head and electrode on the right side, the chimney side, before last winter wich both work fine, but I cannot get the furnace to click on the left or the motor, circuit board, sail switch side. if it is my sail switch I need to find a part number compatible with the OEM part. Thank you for any insight or help I can get.

[JohnB]

Originally Posted by RandyJ55

Hello there;
Once again I'm having an issue with my new TDR clicking after 20 to 25 seconds.

After verifying the integrity of the DSI board , I went through the connections and I suspect my sail switch. Is there a way to test the sail switch other than with a continuity test?

I have a closed circuit on the loop coming from and going to the limit switch so I believe that the limit switch is fine.

I was wondering in anyone had a wiring schematic for the hydroflame 8531-III or one of the series that would include that model. Every year that I have an issue with my furnace I find the answers here. I also have 2 blue wires coming from the inside of the rv , one to the breaker linked with a red wire and the other ,to the sail switch. does it make a difference which blue wire connect to which conponent? I have to sort out this issue because I installed a new burner head and electrode on the right side, the chimney side, before last winter wich both work fine, but I cannot get the furnace to click on the left or the motor, circuit board, sail switch side. if it is my sail switch I need to find a part number compatible with the OEM part. Thank you for any insight or help I can get.

Hi Randy,

Can you explain the sentence in blue what is happening or not happening? And what brand and model of TDR are you using?

Any chance you can post some pics of what you have now?

Let's start there. We had another member with the Rev III furnace not long ago, and when the gas burner ignition started, it stopped the TDR from working and shut down the system. Need to see what your symptoms are.

I'll have to hunt for that post to link it here.

See this link to our FILES section. The 6th file down is a 2003 Service manual. Download the manual; there are wiring diagrams for your furnace in there. Just a heads up, there are all models in that book. You have to make sure you are looking at the correct diagram and options with direct or local flame sense. https://www.sunlineclub.com/forums/d...hp?do=cat&id=6

I hope this helps

John

[RandyJ55]

Hi John, My brother who lives in the RV did something to the thermostat I purchased last year so I bought a new one and haven't yet installed it. So now we're touching the two wires together to start the sequence with him inside and myself at the furnace panel. When the wires are put together the fan starts up and runs but there is no click or signal via the dinosaur brand green TDR to start the ignition cycle after the 20 to 25 seconds. At that point I tell my brother to disconnect the wires and the furnace goes through a cool down cycle, so the ignition prompt is never achieved. I had to replace some spliced wires with newer sections that I purchased on Amazon, namely the blue wires and I wondered if I connected the blue to the breaker instead of the sail switch if it would make a difference. I will look for the wiring schematic but the TDR is the same brand that has been installed since I purchased the RV. One more question. If I do a bypass as a test only for the high limit switch with a wire with alligator clips will that tell me if the limit switch is the issue? I do appreciate your insight and help in resolving these periodic issues

[johnnybgood]

Here’s an interesting story…..

The Atwood 8520-IV-DCCP furnace in my 2000 T2370 acted up last fall. Sometimes (rarely) it would work fine. Other times I’d hear the clicking and smell gas but it wouldn’t fire. Other times it wouldn’t click at all.
Took the cover off the thermostat inside the camper, blew it with compressed air, and now it works as it should.
Go figure.

[JohnB]

Originally Posted by RandyJ55

So now we're touching the two wires together to start the sequence with him inside and myself at the furnace panel. When the wires are put together the fan starts up and runs but there is no click or signal via the dinosaur brand green TDR to start the ignition cycle after the 20 to 25 seconds.

At that point I tell my brother to disconnect the wires and the furnace goes through a cool down cycle, so the ignition prompt is never achieved.

I had to replace some spliced wires with newer sections that I purchased on Amazon, namely the blue wires and I wondered if I connected the blue to the breaker instead of the sail switch if it would make a difference.

I will look for the wiring schematic but the TDR is the same brand that has been installed since I purchased the RV. One more question. If I do a bypass as a test only for the high limit switch with a wire with alligator clips will that tell me if the limit switch is the issue? I do appreciate your insight and help in resolving these periodic issues

Randy,

The wiring diagram for the 85-III with a remote sense for flame feedback is on the top of page 11 in the 2003 Atwood service manual I linked to you, too. This is a direct link. https://www.sunlineclub.com/forums/d...o=file&id=5631

I do believe the Dinosaur board TDR is a solid-state device, and if it is, you will not hear any kind of click when the timer relay reaches its time and sends power to the sail switch and the over-temp sensor, which then supplies power to the igniter board.

If you can post some pictures of the outside of the furnace with the cover off so that I can see how you have wired the system, I can better help. If you are questioning the wiring because you bought something off Amazon, that's OK. We just need to confirm that the igniter board is getting power when the TDR times out.

I'm doing this blindly, with no pictures, but according to the diagram, the white wire on the igniter board connector is the power/run signal to the PC board to time and start the ignition.

If you have a DC volt meter or a simple DC test light probe, unplug the white connector of the PC board and stick the positive probe of the meter or the test light in the connector that would line up with the white wire coming from the hi temp limit switch. Stick the neg lead of the meter or the ground wire of the test light on DC common (-), by the wiring diagram, yellow is DC - which is also on the TDR

Then, the furnace should be fired up. When the TDR times out and the fan motor is running, the white wire at the PC board connector should have 12 VDC voltage. If it does not, that is part of the problem that you have to back into why.

This is a pic of a 85 series -III with the local sense and the original heater type TDR


The sail switch and the over-temp sensor are buried inside the furnace. That makes it hard to test each switch individually, but you can confirm that the blue wire coming back from the T stat feeds power to the TDR and then sends power to one side of the sail switch. Since the fan motor is running, that blue wire should be OK as long as it is feeding the sail switch. That blue return wire becomes hot when you twist the wires T stat together. When the power leaves the sail switch, the wire is white and then jumps to the hi Temp limit switch, and a white wire out of the hi temp limit switch goes directly to the PC board connector. The test above I said to do at the PC connector will help tell a lot.

The sail switch is supposed to be the correct one for the fan blade/motor combo. If the wrong sail switch vane (part of the switch) is used, the sail switch may not turn on when the fan wind is blowing. Or it is mechanically jammed somehow by insects, etc. Since the furnace has worked, the switch might be the right one, but something could now be messed up, not allowing it to be mechanically operate. That is,, if no power is coming to the PC board connector.

Again, let's go back to whether the white wire connector on the PC board has power when the TDR times out. You can do this testing with the LP gas turned off so you cannot get into any LP gas issues. I'm not sure how you are going to do a quick jumper test around the sail switch with the furnace altogether, but with the LP gas off and for testing, yes, you can jump it to see if the white connector wire at the PC board gets power with the motor running and the TDR timed out.

Hope this helps,

John

[RandyJ55]

Thanks John for the information. I have another sail switch which will be here today . I will recheck the wiring and perform the tests that you've referred to. I'll try to get a picture . I can take a picture but have to be able to get it in this forum. You advice has helped in the past and I will get back to you with what I discover . Thank you, Randy

[RandyJ55]

Hi John, my wires including my white wire is spliced and reconnected with plastic coated connectors. I'm not sure if this an issue. I would like to know if there is a compatible harness available and possibly a time delay relay that matches the picture you sent. I will perform the tests and also am curious as to how hard it is to access the limit switch. I saw a YouTube video where the person took off the squirrel cage off the motor and the limit switch was behind it to the right. He had the 8531-III as myself. Thanks for any help you may provide. Randy

[RandyJ55]

Hi John, I ran the test with the test light to the white wire at the unplugged connector and ran the ground clip to the ground connection at the TDR and started the furnace cycle by touching the wires together inside. The problem is that the test light was on from the moment I made the connection instead of after the 20 seconds . When I tested continuity from the same connection, I achieved continuity with my volt ohmmeter . I'm truly stumped as I have a new sail switch, new TDR, and the circuit board tested fine. As a rule in the past, there was a click somewhere on the left side which resulted in the ignition process. Now I hear nothing. I tested the voltage at the breaker and have 13.72 volts on each point. I have continuity for the ground and each blue wire, one to the breaker and the second to the sail switch which brances off to the TDR.I'm wondering if I should have voltage to the sail switch, and when. Somewhere in this sequence, something is amiss and I need to pinpoint the problem. I saw YouTube video where the host stated that the high limit is always closed and only opens when the high limit of heat is achieved. I'm not sure if that's true or the opposite. On previous seasons I've had issues but this is the first one that I didn't hear a distinct click after the blower ran for 20 seconds then the ignition started. I actually have heard it in YouTube help videos as well.

[JohnB]

HI Randy, comments in blue

Originally Posted by RandyJ55

Hi John, I ran the test with the test light to the white wire at the unplugged connector and ran the ground clip to the ground connection at the TDR and started the furnace cycle by touching the wires together inside. Understood

The problem is that the test light was on from the moment I made the connection instead of after the 20 seconds . When I tested continuity from the same connection, I achieved continuity with my volt ohmmeter . I'm truly stumped as I have a new sail switch, new TDR, and the circuit board tested fine.

You may be misunderstanding the sequence of events and what the TDR does. The TDR itself only runs the motor, it does not power the PC board.

Read page 16 in the 2003 Service manual labeled Sequence of Operation - DC Models (STANDARD ONE-STAGE).

Also, read pages 20 through 24 to learn what each component does.

Here is a big picture of what is supposed to happen.

The TDR is used only to control the fan motor.

The Sail switch is activated by the blower wheel blowing the normally open sail switch closed.

The Over temp switch is a normally closed switch that only opens when the heat chamber temp gets too hot.

The T stat supplies 12 VDC power to turn on the TDR relay and sends power to the sail switch at the same time. When the TDR relay engages, which may be 1 to 25 seconds after the TDR is powered, the fan motor runs. This can be seen as soon as the T stat turns on the TDR if it happens in 1 second. When the T stat removes power from the TDR, the blower keeps running for a time to purge the heat chamber of unburnt gases and will keep still blowing some level of heat due to a warm heat chamber until the motor stops.


The T stat wiring also passes power to the sail switch. When the blower blade runs fast enough, it closes the sail switch, which passes T stat power to the over-temp limit switch. The over-temp limit switch, being normally closed, passes T stat power to the PC board. If the over-temp switch is tripped to open up, it breaks the power path until it cools down, then remakes the contact in the over-limit switch

The PC board will get T stat power when the sail switch closes and the over temp switch is still closed. The PC board times for about 15 to 20 seconds before it opens the gas valve and starts the ignition sequences.

The gas valve will click when it opens; this happens about 15 to 20 seconds after the PC board is powered up from the sail switch.

So, with all that, the PC board connector will get power as soon as the sail switch closes on a cold furnace. The motor has to be running to create the wind so the sail switch can pass power to the PC board connector. No motor running, no sail switch closing, and no PC board being turned on.




As a rule in the past, there was a click somewhere on the left side which resulted in the ignition process. Now I hear nothing. I tested the voltage at the breaker and have 13.72 volts on each point.
The click you recall can be the gas valve; if the PC board was turned on, 15 to 20 seconds later, the gas valve should click, and the ignition starts sparking.


I have continuity for the ground and each blue wire, one to the breaker and the second to the sail switch, which branches off to the TDR.I'm wondering if I should have voltage to the sail switch, and when.
Voltage to the sail switch comes from the T stat closing if it is wired correctly.

Somewhere in this sequence, something is amiss and I need to pinpoint the problem.
Yes, you are right, something is amiss. As your test light proved, it sounds like the sail switch is applying power to the PC board. It should have happened as soon as the blower was up to speed.

You can test the PC board by powering the white wire with the LP gas turned off. The gas valve will click after the waiting time period, and the ignition should start sparking. If this is not happening, then something in the PC board, gas valve or electrode is not working.




I saw YouTube video where the host stated that the high limit is always closed and only opens when the high limit of heat is achieved. I'm not sure if that's true or the opposite.

The over temp switch is normally closed

On previous seasons I've had issues but this is the first one that I didn't hear a distinct click after the blower ran for 20 seconds then the ignition started. I actually have heard it in YouTube help videos as well.

There is also something to confirm: the T stat sends the power to run the PC board through the sail with/over-temp with. If, for any reason, the T stat stops sending power, the PC board will shut down. And the blower will keep running until the TDR shuts it down as the time-out purge cycle.

Just because you have the T stat wires crossed does not mean the T stat has stopped sending power Sail switch etc. Your camper may have roof AC system interlocking the furnace. This feature only shows up on the ducted AC systems. If the AC board is opening up the furnace signal, it can shut down the stove, but the blower keeps running until it times out. If you can jump in the test light to the T stat return power at the furnace, you can confirm nothing else is interrupting the T stat power from reaching the PC board.

Please tell us which PC board brand and part number you are using.

We need to see pictures of what your system looks like. See the next section on how to post pics.

Hope this helps

John

[JohnB]

There are 3 ways to add pics.

1. Upload pics to a specific post attaching them at the end of the post.

2. Linking them in from a public viewable web photo hosting service you have.

See here for 1 and 2 https://www.sunlineclub.com/forums/f...html#post86041

3. You can upload pics to the forum in your own personal photo album. Then link them to anywhere in the text of a post. See here on how to create an album. https://www.sunlineclub.com/forums/f...html#post87945

If you still get stuck, let us know.

[RandyJ55]

Thank you for all the helpful information you've provided. I do suspect either the PC board, or the electrode as I believe I learned that the click on the left comes from the PC board as it gets a signal to energize the high intensity wire to the electrode. I will have this pc board retested and provide the part number and brand. It has worked before but it could have failed . I will checked the power going to the PC board via the t stat wires and check the other potential issues . I will try to take pictures and send them . I still have decent weather to get this done and hope to have the issue pinpointed and resolved within a week.

[JohnB]

Hi Randy,

This post may help "IF" you have to buy a new PC board. https://www.sunlineclub.com/forums/f...tml#post160003

The Dinosaur FAN 50 plus pins, https://www.dinosaurelectronics.com/Fan_50_PIN.html control board does not require a TDR, as the motor timing function happens on this control board. It also does not need a remote sense probe as it will make the flame sense directly from the electrode. There are a small number of wiring changes, but it does help eliminate parts that go wrong. This board mimics what is in the 8500 series Rev IV furnaces, the next generation of controls Atwood created after your furnace was made.

Also, you asked where you can get a TDR that looks like the original Dometic discontinued that original heater-type timing relay. While there was one aftermarket maker of one, it was a lot bigger in size, and where to mount it was not a direct drop-in mount like the old one. The Dinosaur TDR is the better choice, but it can have issues like in the post I linked above. You are not have that electrical noise feedback issue, yet anyway, but as I said, if you have to get a new PC board, the Fan Plus 50 with pins eliminates the need to have a TDR.

Good luck with your troubleshooting.

John

[RandyJ55]

John, the PC board is 31501 . It's a fenwal made in China. I tested the blue wires at the sail switch when the two thermostat wires were touched and got 12.72 volts. I checked the voltage at the white wire leaving the sail switch when the sail switch was closed and got 12.72 volts there .I wonder if there is an issue at the plug end leading to the circuit board or the circuit board itself. I may have to run the test you referenced which requires the gas being turned off . I will try to get the board tested again. I need to
begin the process of elimination so I can pinpoint the issue. I installed the board in 2021 and it worked ,2 winters. I need to read your posts again and see which wire induces the igniter to energize the high tension wire . I also have to check the photo process you referenced. I'll get back to you soon. I have to figure this out soon. Thanks again .

[RandyJ55]

My camper does have a roof AC system which has vents in the ceiling.. it has never interfered before. How could I tell if it is interfering with the furnace. I'm not even sure where the control board is. Im going back to London k at the furnace again on the chimney side to see if anything is unplugged. I will take some pictures and then figure out the process.

[RandyJ55]

Hi John, I took out the ,PC board but haven't got a chance to test it yet but I will put back in the chimney as I took it out to make sure all the connections were good . I will reinstall the PC board and reconnect all the wiring while turning off the gas to run the test on the white wire going into the PC board to make sure it has voltage with the TDR timed out. I plan on doing this later today. I'm pretty determined to sort this out . I'll get back to you shortly.

[JohnB]

Hi Randy,

Many of the ducted air systems have one thermostat that controls both the furnace and the air conditioner. They were made Dometic.

If yours has one thermostat to control both the air conditioner and the furnace or did at least originally, then the newer air conditioner control boards up in the ceiling had an interlock contact between the furnace and the air conditioner. The interlock was so that you cannot run both air conditioner and furnace at the same time. if that interlock has a problem it can interrupt the furnace signal. it would be like uncrossing the two wires that you were crossing now, this effect could be an intermittent thing that would shut the flame down on the furnace just like you unhooked or two wires.

Since you’re twisting only two wires to make the furnace run, I can’t tell if you have an independent thermostat for just the furnace. and it might even say Atwood on the cover. If Atwood Tstat was the original one, that means that your furnace is not tied in with the air conditioner

So this comes back to you let us know if you’ve got two completely separate thermostats or you’ve got combined one and it appears that you’ve done something different with the thermostat. I only bring this up as you’re going through a troubleshooting thing that is doing strange things and not allowing the Furnace to ignite it could be a potential problem, but it only means it’s a problem if you have two independent thermostats

Good luck with your testing today. The Fenwall control board, if that’s the original one there may be a problem with that but you could test it with the white wire in the connector board. Again as long as the ground wire in the connector is correct. when you put 12 V power to that white wire, after a short approx 20 second delay, the ignition sequence should start and you’ll hear a click of the gas valve and snapping of the igniter. you can do this all with no Propane on, you just testing that the board actually physically works

Good luck with your hunt today

John

[RandyJ55]

Hi John, I went and had the DSI board tested at Meyers RV in Bath, NY and it failed. The technician said he cleaned all contacts, used pressurized air and there was nothing. This board lasted 3 winters so I ordered another one to use as I investigate the other other one you mentioned with the built in TDR. I'm curious to know where the wires to the current TDR would be rerouted to. I will follow the link and if it's more durable and will resolve my TDR issues in the past, I will probably purchase it soon. The new board 31501 will be here Monday and I will go through the reassembly process and give it a try. At least there will be decent weather this week to work with. I'll keep you posted on the post installation furnace test. Thanks again

[RandyJ55]

Hi John, after installing the new DSI board, nothing works and it's the same part number from the same supplier as the last one. When touching the wires together,bthe fault like for the power supply in the converter inside the rv comes on. There is no fan, nothing. I am going to put the old one in to see if the fault light stays off and at least the fan cycles. That way I can return the new DSI board. This has been a long and tedious process . I tested the fan alone by using a 12 volt ATV battery just to verify that it was not the blower motor, which it wasn't. It may also be that the plug for the old DSI board is not compatible with the new board. I'm not sure what is up but I will try the old board again first .

[RandyJ55]

I checked the old circuit board and have a wire issue. Every time my brother touches the red and white thermostat wires together, the light comes on in the converter relative to the fuse indicating a fault somewhere in the furnace wiring. There must be a wire that is messed up somewhere because everytime I remove the red wire from the circuit breaker terminal the light goes out. I'm not sure if there is an issue with one of the ground wires . I will try to sort this out but this is the first time that I ran into nothing but a fault at the converter coming on while touching the two wires together. I believe I can rule out the circuit board now and start looking at the harness and some of the connectors.

[RandyJ55]

Hello again, Im still at a loss as to what is causing the fault or the flashing light in the power box( converter) at the fuse location for the furnace when the two thermostat wires are touched together. I've ruled out the new circuit board as this fault is happening with both. Fortunately,,it's still not real cold here so I have time to sort this out. If there were any specific areas that you could point to which would cause a fault, I would appreciate it. What I can tell you is when the two thermostat wires are put together nothing happens in the furnace area but when the red wire is removed from the bottom terminal of the circuit breaker, the light goes out.When i connect the blower wires to a 12 volt battery, the blower runs. This is the first time this particular issue has surfaced. Something is crossed in the wiring or there is a ground issue. Could you give me some ideas of what to look for? Before I switched the circuit board, the blower would cycle but the ignition would not initiate to complete the blower to ignition to then heat , cool, and shut down. The circuit board testing failed so I got another board but while sorting through this process, I must have done something wrong in the harness. I have a new board, TDR, sail switch, the limit tests closed and I have voltage from the converter. I would appreciate any insight .Thank you