Community Forums

Charlie 5320 · 02-03-2021, 11:21 AM

Quote:

Originally Posted by TimmyB

In the PCI board, they are two separate systems with two separate sensors (heat pump sensor in bedroom, furnace sensor in living room). I can (and most often, do) have them on separately. Since we have no "reliable" heat from the furnace, on a cold night (55 or below), we'll just put the rooftop heat pump on at about 67 with fan on constant HIGH. She works like she's supposed to the entire night. Only if I get up in the morning and try to warm the living room up with the gas furnace do I get any issue with the rooftop heat pump unit, and it only happens when the furnace has the issue. It takes 15 to 20 minutes to manifest itself, but it almost always does.

Ok, sounds like the furnace is going out on a safety circuit. Does it lite and work right ever? To test the sail switch, you will need a meter. On a call for heat, the blower should start, makes the sail switch, couple seconds the igniter, should start sparking, the gas valve should open, burner should lite, and should run this way till there is NO call for heat. If it shuts down early, you have to measure the voltage on the sail switch. Measured to ground, should be 12v on BOTH sides of the switch. Test this switch first. If it is open, no power on both sides, then you have to find out why. Wasp nest in the flue? Motor running too slow? Something blocking the air flow?

Charlie 5320 · 02-03-2021, 11:27 AM

Quote:

Originally Posted by TimmyB

No, I have no idea where to even look for these dip switches? Where might I find them?

Do you have the manual that came with the coach? Should be in there how to do a setup. It does sound like the furnace input back to the system is causing the problem. I would think the dip switches is setup right beings the furnace does try to work. If you have 2 heat pumps, there will be a set of dip switches in each control, plus maybe on back of the stat.

TimmyB · 02-03-2021, 11:31 AM

Quote:

Originally Posted by Charlie 5320

Ok, sounds like the furnace is going out on a safety circuit. Does it lite and work right ever? To test the sail switch, you will need a meter. On a call for heat, the blower should start, makes the sail switch, couple seconds the igniter, should start sparking, the gas valve should open, burner should lite, and should run this way till there is NO call for heat. If it shuts down early, you have to measure the voltage on the sail switch. Measured to ground, should be 12v on BOTH sides of the switch. Test this switch first. If it is open, no power on both sides, then you have to find out why. Wasp nest in the flue? Motor running too slow? Something blocking the air flow?

Yes, that's the maddening part. The start up is exactly as it should be. For example, let's say it's 63 degrees in the living room (as measured by the thermostat) and you tell the furnace to take it to 70 (via the PCI interface).

(1) The fan will begin to blow.
(2) After 15 seconds, you'll hear the burner light. It will continue to burn and heat the room for approximately 15 minutes, give or take.
(3) Then, even though the PCI panel is telling you the temperature has climbed to only 64 or 65 (still calling for heat), you'll hear the burner kick off. After a couple of minutes, it usually kicks back on. It might even do this 2 or 3 times.
(4) After a short while longer, the burner will kick off for good (even though the temp is nowhere near the 70 you set it at).

At this point, the system is unresponsive to any commands. You can turn the system "OFF" in the PCI panel (and it will display "OFF") but the fan keeps running and producing no heat. The ONLY way out at that point is to kill the entire house using the battery disconnect. Once that is done, you can try again. It makes the furnace unusable overnight, as it will continue to draw in very cold air and you'll wake up to a freezing motorhome.

TimmyB · 02-03-2021, 11:34 AM

Quote:

Originally Posted by Charlie 5320

Do you have the manual that came with the coach? Should be in there how to do a setup. It does sound like the furnace input back to the system is causing the problem. I would think the dip switches is setup right beings the furnace does try to work. If you have 2 heat pumps, there will be a set of dip switches in each control, plus maybe on back of the stat.

I do have the manuals. I have only one heat pump unit. The living room unit is AC only.

I'll see what I find out in there.

Charlie 5320 · 02-03-2021, 11:44 AM

Quote:

Originally Posted by TimmyB

Yes, that's the maddening part. The start up is exactly as it should be. For example, let's say it's 63 degrees in the living room (as measured by the thermostat) and you tell the furnace to take it to 70 (via the PCI interface).

(1) The fan will begin to blow.
(2) After 15 seconds, you'll hear the burner light. It will continue to burn and heat the room for approximately 15 minutes, give or take.
(3) Then, even though the PCI panel is telling you the temperature has climbed to only 64 or 65 (still calling for heat), you'll hear the burner kick off. After a couple of minutes, it usually kicks back on. It might even do this 2 or 3 times.
(4) After a short while longer, the burner will kick off for good (even though the temp is nowhere near the 70 you set it at).

At this point, the system is unresponsive to any commands. You can turn the system "OFF" in the PCI panel (and it will display "OFF") but the fan keeps running and producing no heat. The ONLY way out at that point is to kill the entire house using the battery disconnect. Once that is done, you can try again. It makes the furnace unusable overnight, as it will continue to draw in very cold air and you'll wake up to a freezing motorhome.

OK the furnace is going OFF on a safety. There is 3 things that can cause this. Motor slowing down when it gets warm, there for the sail switch will open, and shut the furnace down, goes thru a retrial. My money is on the ground from the control board. The control has to ground thru the flame to the sparker. If there an erratic flame it won't be able to ground. The little rod that does the sparking to light the flame serves 2 purposes, produces the spark to light the flame and to ground after the flame is established. The little sparker rod HAS to be in the flame, and should glow red. IF it loses ground it will go thru a retrial to flame again. It will do this 3 time before it goes into lock out. In lock out the blower will continue to run until you do a power down reset.

TimmyB · 02-03-2021, 12:39 PM

Quote:

Originally Posted by Charlie 5320

OK the furnace is going OFF on a safety. There is 3 things that can cause this. Motor slowing down when it gets warm, there for the sail switch will open, and shut the furnace down, goes thru a retrial. My money is on the ground from the control board. The control has to ground thru the flame to the sparker. If there an erratic flame it won't be able to ground. The little rod that does the sparking to light the flame serves 2 purposes, produces the spark to light the flame and to ground after the flame is established. The little sparker rod HAS to be in the flame, and should glow red. IF it loses ground it will go thru a retrial to flame again. It will do this 3 time before it goes into lock out. In lock out the blower will continue to run until you do a power down reset.

So, I just went outside and took the door off the furnace. I can see all the wiring and I can see the control board that they replaced.

I have a voltmeter, although I'm pretty limited in my knowledge of how to work it. Is this something that I can diagnose, given these conditions, or should I just pass this on to REV?

Charlie 5320 · 02-03-2021, 12:52 PM

Quote:

Originally Posted by TimmyB

So, I just went outside and took the door off the furnace. I can see all the wiring and I can see the control board that they replaced.

I have a voltmeter, although I'm pretty limited in my knowledge of how to work it. Is this something that I can diagnose, given these conditions, or should I just pass this on to REV?

You can do it !! Start the furnace and watch the flame where the sparker rod is. It HAS to be in the flame to work correctly. Should be a green screw on the board, make sure there is a wire from that screw to ground. If the flame is wavering around it may be losing the ground that way. Watch the thing run until it quits, if it trys to start again immediately after it quits, it's losing proof of flame. Make sure there is NO wasp nests in the discharge of the flue, they love to build nests in there.

TimmyB · 02-03-2021, 12:55 PM

Quote:

Originally Posted by Charlie 5320

You can do it !! Start the furnace and watch the flame where the sparker rod is. It HAS to be in the flame to work correctly. Should be a green screw on the board, make sure there is a wire from that screw to ground. If the flame is wavering around it may be losing the ground that way. Watch the thing run until it quits, if it trys to start again immediately after it quits, it's losing proof of flame.

OK. Tomorrow morning will be very cool, again. I'll try it out, then.

Thanks, Charlie!

Charlie 5320 · 02-03-2021, 12:58 PM

Quote:

Originally Posted by TimmyB

OK. Tomorrow morning will be very cool, again. I'll try it out, then.

Thanks, Charlie!

Send me a pm or email if I don't get on in the morning. You can do this.

TimmyB · 02-03-2021, 01:03 PM

Quote:

Originally Posted by Charlie 5320

Send me a pm or email if I don't get on in the morning. You can do this.

Will do. Thanks, again!

YC1 · 02-03-2021, 05:05 PM

Tim, can you get the actual model number and even better, look up a schematic and post.

For the furnace mostly.

TimmyB · 02-03-2021, 05:18 PM

Quote:

Originally Posted by YC1

Tim, can you get the actual model number and even better, look up a schematic and post.

For the furnace mostly.

I took pictures today to help me with the wiring (for tomorrow) but of course, the label has the model number just beyond where I can make it out. It does show the Item # as 35425SU and when I type that in to a search, it takes me to a page where one Dometic Furnace (DF) is replacing bunches of others.

I will get it in the morning when it's light out and I'm not losing tools and parts in the dark!

I can post the pics here, if you think that will help you determine what we're up against. (?)

HVAC ZACH · 02-03-2021, 08:34 PM

Not sure if you got this fixed yet, but it soumds to me like your furnace is tripping on a limit switch. During the sequence of operation if your furnace it has to prove induced draft, light burner, then prove flame. If the burner gets too hot during operation or the flame cannot be drafted effectively it will trip a limit. When this occurs the usual operation of the furnace board saftey is to de-energize the gas valve and run the blower continuously to ensure draft and cool the heat exchanger. This will not stop until the call for heat is cycled off by the thermostat or power is cycled off to the control board. You mentioned the fan runs continuously and will not turn off unless you cycle power. Is the fan switch turned to continuous operation? Also how much air does the furnace move through the coach? I have found the fans to be installed backwards or not turning in the correct direction causing a multitude of problems. It also sounds like the main contol pannel PCM could be malfunctioning. just my thoughts. hope this helps

Zach

TimmyB · 02-03-2021, 08:53 PM

Quote:

Originally Posted by HVAC ZACH

Not sure if you got this fixed yet, but it soumds to me like your furnace is tripping on a limit switch. During the sequence of operation if your furnace it has to prove induced draft, light burner, then prove flame. If the burner gets too hot during operation or the flame cannot be drafted effectively it will trip a limit. When this occurs the usual operation of the furnace board saftey is to de-energize the gas valve and run the blower continuously to ensure draft and cool the heat exchanger. This will not stop until the call for heat is cycled off by the thermostat or power is cycled off to the control board. You mentioned the fan runs continuously and will not turn off unless you cycle power. Is the fan switch turned to continuous operation? Also how much air does the furnace move through the coach? I have found the fans to be installed backwards or not turning in the correct direction causing a multitude of problems. It also sounds like the main contol pannel PCM could be malfunctioning. just my thoughts. hope this helps

Zach

Hi, Zach. Thanks for your suggestions. No, we had resolved this problem, yet. I am planning on doing some inspections and testing tomorrow morning.

It very much sounds like it could be an overheating problem. The furnace is controlled by a touchscreen panel (Precision Controls Inc) and once the problem occurs, it indeed cannot be stopped without using the battery disconnects for the whole coach. It doesn't matter if the fan was on high, low, or auto, at least not that I've discovered.

As for air flow, I've surely not noticed what I would consider a lack of sufficient flow, but I don't have another Bounder to compare it to. I do know that it takes what I feel is a long time to heat the living area compared to our old fifth wheel, which would suffocate you with heat within fifteen minutes.

Feel free to add any thoughts you want to add. Thanks again.