Compressor turns on with furnace/furnace turns on with compressor. Any ideas?

[redhatengineer]

We have a 2021 Imagine 2970RL with a coleman mach 15 AC. When using my AC, the furnace initiates when the compressor in the AC initiates (not a heat pump, which is not installed. The actual propane furnace lights, the blower motor turns on, and it starts producing hot air while the AC produces cold air) I figured i could work around this by disabling the furnace, so I popped the cover and flipped the furnace off, so only the blower motor turns on with the compressor. This is when I found that if the furnace isn't actually on, the blower motor turns off after about 90 seconds...and so does the AC compressor. Conversely, if I turn on the furnace, the AC compressor turns on (NOT the fan, the compressor) and will run indefinitely until the furnace turns off (or at least as long as I let it run which was about 30 seconds), To clarify, this isn't the AC unit fans turning on with the heat as might be expected. This is the actual compressor turning on, pulling 1000+ watts and 11-14 constant amps (we have a micro-air easy start installed, this issue predates that installation).

Has anyone had an issue similar to this? Basically what this means is I have to pull the wires out of my thermostat and hard wire the AC unit on if I want it to work (at which point it does indeed function correctly, but still turns on the blower motor for 90 seconds. the compressor just doesn't turn back off as I'm supplying 12 constant volts). Obviously I'd love to have an actual rv repair person have a look but getting into a GD dealer will take us 3-5 months.

[redhatengineer]

So I've been able to work around the issue by disconnecting the orange furnace wire that travels from the thermostat to where it lives inside the AC where it connects to a larger gauge wire that runs to I assume the furnace. Neither of these wires connect directly to the ac, so this suggests to me that there's a short in the wiring harness between the thermostat and the ac so when the compressor wire is charged, it's charging the furnace as well. I'm not entirely sure why it then turns off the compressor when the furnace blower motor turns off. Maybe the furnace is sending a kill signal back to the thermostat that's shorting at that same place and tripping the compressor to stop also? I'm not familiar enough with how the system works too know for sure.

So I guess I'll go find a replacement harness and test my theory, then install it myself. This however did expose another issue; the relay for the compressor in the control box is sticky and doesn't always turn off when the thermostat tells it to, so if it's on auto the fans turn off when it hits temp but the compressor keeps running. Couple taps on the control box will turn it off so I'm pretty confident the relay is borked. So I'll be getting a new control box too. RV life is the best lol

[DECelt]

We have a 2021 Imagine 2970RL with a coleman mach 15 AC. When using my AC, the furnace initiates when the compressor in the AC initiates (not a heat pump, which is not installed. The actual propane furnace lights, the blower motor turns on, and it starts producing hot air while the AC produces cold air) I figured i could work around this by disabling the furnace, so I popped the cover and flipped the furnace off, so only the blower motor turns on with the compressor. This is when I found that if the furnace isn't actually on, the blower motor turns off after about 90 seconds...and so does the AC compressor. Conversely, if I turn on the furnace, the AC compressor turns on (NOT the fan, the compressor) and will run indefinitely until the furnace turns off (or at least as long as I let it run which was about 30 seconds), To clarify, this isn't the AC unit fans turning on with the heat as might be expected. This is the actual compressor turning on, pulling 1000+ watts and 11-14 constant amps (we have a micro-air easy start installed, this issue predates that installation).

Has anyone had an issue similar to this? Basically what this means is I have to pull the wires out of my thermostat and hard wire the AC unit on if I want it to work (at which point it does indeed function correctly, but still turns on the blower motor for 90 seconds. the compressor just doesn't turn back off as I'm supplying 12 constant volts). Obviously I'd love to have an actual rv repair person have a look but getting into a GD dealer will take us 3-5 months.

I would get GD to pre-authorize a mobile rv tech to fix it. You will have to pay the service call, but these self-employed RV techs are typically far better at solving problems than RV dealership techs.

[redhatengineer]

I would get GD to pre-authorize a mobile rv tech to fix it. You will have to pay the service call, but these self-employed RV techs are typically far better at solving problems than RV dealership techs.

At this stage I think I've targeted the issue down to the wiring harness between the thermostat and the ac unit. If that's all it is, the worst of the job is going to be getting the new harness into the wall. hopefully the old one isn't tied down anywhere too tightly and I can just use that as a fishing line for the new one. If testing with a new harness doesn't improve the situation I'm going to be talking to GD until they agree to pay the full freight on a mobile tech. I've had more unexplained problems with this brand new trailer than i had with my busted up 10 year old coachman.

[openrangeowners]

You stated "orange wire" - that is for the heat pump. There should be a white wire for the furnace. The mixup sounds like the control module in the AC unit or they connected the furnace to the heat pump control and since you don't have a heat pump it runs the furnace in addition to the AC.

The wiring bundle is as follows:

Green - fan normal speed
Grey (or brown) - fan low speed
Yellow - AC compressor
Orange (not used on yours) - Heat Pump
White - Furnace
Red - 12VDC
Black (or blue) - ground

Look for a wiring diagram

[redhatengineer]

You stated "orange wire" - that is for the heat pump. There should be a white wire for the furnace. The mixup sounds like the control module in the AC unit or they connected the furnace to the heat pump control and since you don't have a heat pump it runs the furnace in addition to the AC.

The wiring bundle is as follows:

Green - fan normal speed
Grey (or brown) - fan low speed
Yellow - AC compressor
Orange (not used on yours) - Heat Pump
White - Furnace
Red - 12VDC
Black (or blue) - ground

Look for a wiring diagram

In my case, this is not the wiring schematic used. the wiring harness in my trailer (as it was originally wired), includes:

red (12 vdc)
blue (ground)
white (low fan)
green (high fan)
yellow (compressor)
orange (furnace)

there is a brown wire that was snipped short and never attached to the original thermostat, and isn't connected to anything inside the AC unit. I did look up the wiring diagram and I've seen several other GD units that have the same harness set up as I do. I manually tested all the applicable wires to ensure they powered the individual portions of the system as i've described, and they do. Which isn't to say there isn't a wiring issue i'm unaware of, but based on the tracing i've done it doesn't seem to be as the result of using the wrong wire. While you CAN install a heat pump here, there isn't one installed in my unit and I don't see any other control module in the AC unit where the orange wire would connect to. It is clip connected to another orange wire that runs back out of the ac unit into the ceiling and disappears. All the rest of the connected wires run as expected into the control unit, which seems to be the individual control unit, with no post to control a heat pump or any of the dual-zone control options. Where would the heat pump control normally be? I'd love to discover this was the case and an easy fix hahaha

I'm also not sure why this would result in the furnace turning on when I apply direct 12v to the compressor wire outside of the thermostat.

[openrangeowners]

The furnace should have a connection in the control box as well (to the furnace)

Wiring diagram for Thermostat (ignore the Bluetooth parts - same wiring as yours) .... https://www.airxcel.com/docs/default...1.pdf?sfvrsn=6

Wiring Diagram for AC unit (may not be exactly the right model ...) http://old.rvcomfort.com/rvp/pdf_doc...76a657_315.pdf

[redhatengineer]

The furnace should have a connection in the control box as well (to the furnace)

Wiring diagram for Thermostat (ignore the Bluetooth parts - same wiring as yours) .... https://www.airxcel.com/docs/default...1.pdf?sfvrsn=6

Wiring Diagram for AC unit (may not be exactly the right model ...) http://old.rvcomfort.com/rvp/pdf_doc...76a657_315.pdf

It looks like I have Control Box 8330-752 (or equivalent), which has only fan high, fan low, compressor, 12vdc, and the freeze sensor posts. There's no direct control box connection to the furnace wire, where they appear to have used orange in my case instead of white for whatever reason. I've attached some photos of the control box and the furnace wire (orange). The lighter gauge furnace wire comes out of the wiring harness that runs to the thermostat and previously clipped in with the heavier gauge wire that runs back out of the unit without connecting to anything else in the unit.. in the photo you can see i've disconnected them and just capped off the thermostat end with another joint clip for safety. disconnecting this wire prevents the furnace from turning on when the compressor wire is charged.

[openrangeowners]

Did you say you have an extra wire (Brown) in the wiring harness from the AC unit to the Thermostat - wonder if the Orange wire is shorting to the Yellow wire somewhere? If so, maybe switch control of the furnace to the brown wire (both at the thermostat and the control box) and see if the problem still exists (that would tell you if there was a short in the wiring). Might save having to tear apart the walls to fish new wire ....

When you applied 12V to the yellow wire at the control box and saw the furnace come on indicates a short somewhere between the yellow wire and orange wire (unless you still had both connected to the thermostat .... then there might be a short in the actual thermostat).

[redhatengineer]

Did you say you have an extra wire (Brown) in the wiring harness from the AC unit to the Thermostat - wonder if the Orange wire is shorting to the Yellow wire somewhere? If so, maybe switch control of the furnace to the brown wire (both at the thermostat and the control box) and see if the problem still exists (that would tell you if there was a short in the wiring). Might save having to tear apart the walls to fish new wire ....

When you applied 12V to the yellow wire at the control box and saw the furnace come on indicates a short somewhere between the yellow wire and orange wire (unless you still had both connected to the thermostat .... then there might be a short in the actual thermostat).

Hey that's a great and obvious idea I hadn't thought of. I'll have to find a conductor to pigtail off of it but I think I have something in the tool box. Thanks for the help! I'll update with how it goes