A-C question.

[DickWells]

Just last night, our trailer A-C compressor started refusing to shut down when the temp gets to the pre-set level and the D-C fan shuts off. I've never gotten into A-C of any kind, other than re-charging a few units in cars/pickups, so I'm looking for some direction from the experts. Where do I start looking? No, I haven't pulled out my RV service manual, which has helped me out quite a few times, like with the furnace, but the A-C is more intimidating for me. Sound like a re-charge is in order, or maybe a relay, or capacitor, or ----------? Meanwhile, we're using it by waiting until the 12V fan shuts of at the set temp, and the fuze panel is open and we just switch off the 120V breaker to the compressor until we need cool air again. Any and all suggestions will be greatly appreciated.

DW

[arveetek]

Sounds like the relay is sticking for the compressor. The Duotherm brand is really bad about doing this, although Colemans will occasionally do this.

I assume you have ducted A/C with a large square return air grille in the ceiling with a filter? If you have a Duotherm model, remove the air return grill and filter, and locate the silver box with the 120V wires and 12V wires going into it: this is the relay box. Flip the breaker back on, and then whack the silver box with your hand. This will sometimes loosen the relay and allow the compressor to shut off. If it does, the you know for sure this is the culprit. You will need to replace the relay box as whacking it is only a temporary fix.

If whacking the box doesn't help, locate the braided cable bundle that goes from the upper A/C unit and plugs into the side of the silver relay box. Unplug this bundle of wires. If the unit shuts off, then you know the problem is in the control assembly.

It's possible that the thermostat is defective and is not telling the relay box to shut down, but I've never seen this happen. It's always the relay box sticking. You can read the wiring diagram on the silver box and do some troubleshooting to see if the thermostat is sending power to the relay box when it shouldn't be.

Locate the part # on the relay box and call your local RV dealer to see if they have one in stock. Don't be alarmed if they tell if you the control kits have been discontinued, because Dometic (maker of Duotherm) has discontinued most of the control boxes they used for years. However, if you don't want to convert to the newer style thermostat and box, call me at work, as I bought a bunch of these kits when I caught wind that Dometic was discontinuing them.

If you have a Coleman, let me know. It will be a slightly different setup.

My work # is 417-358-4640. Ask for Casey.

[DickWells]

Well, hey!, you jumped on that one, Casey! Thanks. And, yes, it's a Duo Therm. Having my breakfast coffee, right now, and catching up on my e-mails, but I'm going to get right after that AC, and follow your instructions, soon as I'm through fooling around with old, retired, procrastinating things.

Thanks again.
DW

[torque]

Could be the same problem I had last summer - the temperature sensor. When you look up near the silver box, you should see a 2-wire sensor up against the "radiator" fins. It's attached to a bracket that is shoved into the fins. It has to be attached in the proper place and functional otherwise the AC doesn't know when enough is enough.

[rustyk]

I've had a delightful time with my Duo-Therm Penguin II. I wanted the manual (non-electric) shroud-mounted thermostat; after the third failure I replaced the shroud (different shroud for each!) and had the remote analog electric installed.

I'm on my 3rd remote - the original eventually couldn't hold a temp, the second just didn't work, and the last one turns on the heat strip and compressor at the same time, whether on heat or cool.

This thermostat is being phased out for digital, which naturally needs a different control board.

Fortunately, I took the extended warranty...

[DickWells]

It was the relay. Couldn't make it work by thumping the box, but with the cover off, and the PC board in hand, a quick swat with the butt of a phillips screw driver got the comp to shut down.

I've ordered a relay to be sent to SIL's in Oregon. Will limp along what ever way it takes until I get up there. Looks like an easy solder-suck job on the PC board, and a new relay should work out OKay. If not, I'll be sure to let you know, Casey, and make arangements to get the whole kit from you.

Thanks so much for your quick come-back with great info.

Gotta keep your issue in mind, RUSTYK, because one of our neighbors here has had the same thing going on, IIRC.

Thanks again, DP.

[arveetek]

I'm on my 3rd remote - the original eventually couldn't hold a temp, the second just didn't work, and the last one turns on the heat strip and compressor at the same time, whether on heat or cool.

I can't stand the remote control thermostats! Duotherm, Coleman, and Carrier all experimented with them, and then decided they weren't working out well, and discontinued them. Now Carrier is out of the RV HVAC business, and several other brands are emerging.

If we have a customer's unit with a remote thermostat, we usually talk them into retrofitting in a standard thermostat. They are usually much happier after that.

Casey

[arveetek]

Could be the same problem I had last summer - the temperature sensor. When you look up near the silver box, you should see a 2-wire sensor up against the "radiator" fins. It's attached to a bracket that is shoved into the fins. It has to be attached in the proper place and functional otherwise the AC doesn't know when enough is enough.

Actually, the temp sensor's job is just to shut down the compressor if the evap fins get too cold; it prevents "freezing" of the system. It's inline with the relay, so it only opens the circuit. It can't keep the compressor running after the controls shut down, but it could prevent the compressor from coming on when a/c is selected.

Casey

[a5150nut]

I'm on my 3rd remote - the original eventually couldn't hold a temp, the second just didn't work, and the last one turns on the heat strip and compressor at the same time, whether on heat or cool.

Isn't that the undocumented automatic defrost feature?