No rear Air cond on shore power or generator

Jim in SE Ks · 08-29-2021, 04:50 PM

1998 Winnebago Brave 35WP. Front A/C works fine Shore or generator. If on generator I have the selector switch to front which is required to run both air cond. front works fine when I go to rear thermostat set temp below room temp move therm sw to on I get nothing, no fan no compressor. Shut Generator down, move cord to shore power...Check all 120 vac breakers in coach again, all ok. Move selector switch to Rear go to thermostat push to fan, then to compressor, still nothing, not even fan hum or comp trying to run. I did a full reset of all ac breakers, stiil not working. What should I look for next?

Ray,IN · 09-02-2021, 09:53 PM

Have you tested voltage at that selector switch to make sure it actually works?

Jim in SE Ks · 09-03-2021, 08:21 AM

The only check I've done with the selector switch is to position switch from rear a/cond to front and run generator to run both a/cond and still no rear a/cond. I have checked and reset breakers both at load center and generator. None were tripped, but as a precaution. At present I don't have access to shore power, but will later this month. Thanks for your responce.

Morich · 09-03-2021, 09:04 AM

Morning Jim!
A little more AC to help?
One big thing to keep in mind is that while the air does use 110 Ac to operate, it also needs 12VDC to Tell it to operate by powering the thermostats.

I did a short look on my phone for siring and it looks like on your model, the rear thermostat may have a separate power feed than the front. Quick look using a pretty worthless view you get on a phone but it may be worthwhile to check the DR breakers as well as AC.

I'm away from my PC where I can get a better look at the drawings but checking the dc may fire up the correct thermostat???

Will do some checking shortly for where and which if you do not find them.

Am I correct in that you have the model which requires moving the cord to a generator outlet box, meaning no auto transfer switch? That would make it somewhat more simple to trace and troubleshoot.

Morich · 09-03-2021, 09:39 AM

Doing a bit more looking, I might want to check the battery and ground at that rear thermostat as an easy quick look if a meter is on hand.

I think the power side will likely be okay as it also feeds a number of other things, assuming you don't have other electrical troubles with vents, range hood, water pump?
They use the same power feed on several other things, so we might guess it is not a breaker problem at the thermostat?

If you have a meter to check for power and ground, I might suggest checking these two at the rear therm. There appears to be two plugs and you need to look at the one with the larger 14 gauge wires (purple is battery and green is ground)
Check the ground carefully to make sure it is good as I think the battery will be okay due to so many other things using that lead. The other wires I marked, DD,DE, DF are for the fan speeds, but they need the power and ground to run the fan.

Wire ID guide here:
https://www.winnebago.com/Files/File...ical_guide.pdf

Maybe see if that helps ----when you get cooled and feel like it !!!

Jim in SE Ks · 09-04-2021, 05:43 PM

Yes Morich you are correct about the power cord. For generator I plug in to the generator box. Shore power is same cord plugged into 30 amp pedestal or Rv power box. Thanks for the wiring number sheets. Will try to locate the ones to check when I get back to the MH. The DC breakers located at the selector sw panel have been check. All other DC items, pump etc. are working fine. The front thermostat has the furnace position in addition to the Air Cond fan settings. the rear thermostat only has "off" "fan" and "comp" position.
When I get back to it I need to see whats under the Air Cond shroud and get access and check physical condition of the wires and see if the fan rotates freely. I''ll keep checking in as I can.
Many thanks,
Jim

Morich · 09-04-2021, 07:03 PM

I try to not get on the roof if I can avoid it but sometimes we have to do what we have to do!.

That's where I was kind of looking for easier places to check and wanted to point out that the thermostat is just a switch that uses 12volt power to tell the 110 volt power to run the bigger stuff. That lets them use small wires that fit under the cover on the wall better than the big wires that would do to handle the higher voltage.
So when the heat or air don't run, wee need to remember to check the smaller wires and voltages to see if they are good.
Kind of like a little master making a big guy do the work, so we gotta know the little guy that makes the decisions is doing it right before assuming the big guy is not doing his thing!

Your choice and you have to do any work involved but that is where I might favor taking the thermostat off to make sure the plugs are still plugged into the back and testing that the purple wire has 12VDc and green has ground. So when we set the thermostat switch right, the three small purple wires are for the different fan speeds. If one of the big wires is loose, nothing happens, so I look for the easier places to check first!

I used to climb towers as high as 200 feet but now I don't even want to go to the roof! I used to slip over the line from Lamar, Mo. to get a beer in Pittsburg when I was nineteen but I don't do that any more either!

But those three wires look like they go from the thermostat to the roof unit, and at that point, they don't give us much help if we don't get it from the roof AC builders!
This is from the wire ID chart here:
https://www.winnebago.com/Files/File...ical_guide.pdf

Click this snip to get it to come up bigger to read?

Jim in SE Ks · 09-05-2021, 10:52 AM

Morich, getting up on the roof was not going to be ME. At 82 yrs, I haven't been on that roof for about 3 years. Don't have the legs for that ladder anymore. Will do what I can to check the things I can with the wiring and leave the climbing to the younger generation. I will make good use of your wiring /circuit info. I do appreciate the help.
Jim

Jim in SE Ks · 09-07-2021, 08:51 PM

Morich and all lookers, problem turned out as Morich suggested, lack of 12 Volts DC to the Rear Air Cond. Problem was the thermostat. Pulled the front thermostat (same wiring except the white wire for the furnace) The 2 plugs were the same so that swap and using the generator for power fixed the no air problem. The original old 1998 analog thermostat has been replaced by a digital unit, so supposed to be compatible. I have one located about 50 mile away, so will take the old one to compare wiring at the plug. I will try to make a final post when I get the new one plugged in. Many thanks to Morich and all interested.
Jim