Forum Discussion

RVNewbie1972's avatar
RVNewbie1972
Explorer
May 06, 2014

AC Unit not working

Hello Everyone!

Thanks again for all your help last year with some assorted problems I had. Having bought a used Class C, and cutting my teeth for the first time, I needed a LOT of help with things which I got from you!

OK- Now for the issue. Late last season, I came to find that the AC unit was blowing air, but now blowing cold air. I put it on the back burner to deal with later, and not later is here.

First- The Numbers on the AC unit: It's a Duo-Therm Model 57915.603 Product # 991731243 Serial # 3207430.....Roof Mounted Unit with 3 knobs on the unit itself...It's original with the RV which is now 21 years old

In going through the diagnostics this spring, I am finding that everything is working and that the unit SEEMS to be blowing cold air, however that was checking it in 50-Degree weather......So the air coming out seemed cold to be however I remember quite vividly last fall when it was 100 Degrees out and the AC unit was basically a roof-mounted fan.

So- How can I check to make sure if it's working for sure? I don't want to wait until Mid-June when the weather is 100 degrees again to find out that the AC is indeed kaput? I don't have a problem spending the $$$ to replace the unit, however I don't want to do it unless I have to.

Bringing it to someone to look at it isn't really an option; I'm not interested in spending $200 to have someone tell me "Yep- it's broken and needs to be replaced" when I can find a new one for under $600

So- How to I check to make sure it isn't working? And assuming it's broken and isn't feasible to fix, what are my options to replace the unit itself? I don't care what I replace it with as long as it does the trick.

Now back to last year- Our inaugural year RVing was awesome! We did a trip to the White Mountains of New Hampshire, we did a trip to Niagara Falls (Stayed on the Canadien side) and Letchworth Park, and about a dozen or so local trips....It really was quite memorable!

Thanks in Advance,

Nick

7 Replies

  • j-d's avatar
    j-d
    Explorer II
    Yo, Jose! I looked up the wiring diagram and saw where OP's unit "Should Have" a combined Fan/Compressor Capacitor (probably marked FAN, HERM and COM or no marking on Common) plus what seems to be an optional Start Kit made up of Capacitor and PTCR Device.
    My best guess is that the HERM side of the combined cap is failed OPEN and isn't shorted but also isn't letting the Compressor start up. Confirm this with me, I think I'm right and this is what I was going to go over with OP:
    1. Compressor CANNOT run if Run Cap (the HERM side)is BAD.
    2. Compressor CAN run on Shore Tie IF Run/HERM is Good and Start Cap and PTCR are disconnected.
    3. Compressor CANNOT run if Start Cap and/or PTCT BAD even if Run/HERM is GOOD.
  • Mine would try to start, bog my generator, then release the generator and the compressor would never got going. Buddy of mine that does HVAC for a living said the compressor almost never goes out on an RV A/C unit. He said it is almost always the capacitors. I opened my A/C up and the caps. were all leaking. Replaced all 3 caps. and the A/C now works great! Be CAREFUL with capacitors. You need to know how to discharge them as they store high voltage.

    Jose
  • j-d's avatar
    j-d
    Explorer II
    Cobra's right. If you aren't sure the compressor is working at all, take the cover off the unit. Be sure you're away from all contacts and moving parts like the fan. Have somebody inside start the A/C. There will be two tubes into the top of the compressor. The thinner one should be warm/hot. The thicker one should be cool/cold, in just a matter of a minute.
  • If you want to know if it is working...it should blow air out about 20 degrees
    colder than the air temp. in side the rv. So if it is 75 in the rv, the air coming out of the air cond. should be around 55 degrees.
  • j-d's avatar
    j-d
    Explorer II
    Go to Chris Bryant's Service Manuals Page, go down to the Air Conditioning, download the manual and go to Page 58 where you should find a Wiring Diagram.
    Let me know when you're there, and tell me - Does your Meter do Capacitance?
  • j-d wrote:
    Let me be sure I understand:

    1. Fan works but not Compressor (air moving but not chilled).
    2. A/C has manual controls on it (no wall thermostat).

    If that's the case, my thoughts are:

    1. Switch defective or in wrong position
    2. Problem with Defrost Sensor (if it has one - Our Coleman with controls on unit does NOT)
    3. Bad Compressor or Bad Thermal Safety on Compressor (unlikely)
    4. Bad Run Capacitor on Compressor (a prime suspect)

    Are you comfortable getting onto the roof of the RV and digging into an electrical device?

    Do you have a Clamp-On Ammeter?

    A Digital (or old Analog) Volt/Ohm Meter?

    If you have a meter, can it measure Capacitance (MicroFarads (maybe labeled uF")?


    Yes, I have no problem being on the roof, Yes I have no problem doing work, and Yes I have a Digital Multimeter. What's next?
  • j-d's avatar
    j-d
    Explorer II
    Let me be sure I understand:

    1. Fan works but not Compressor (air moving but not chilled).
    2. A/C has manual controls on it (no wall thermostat).

    If that's the case, my thoughts are:

    1. Switch defective or in wrong position
    2. Problem with Defrost Sensor (if it has one - Our Coleman with controls on unit does NOT)
    3. Bad Compressor or Bad Thermal Safety on Compressor (unlikely)
    4. Bad Run Capacitor on Compressor (a prime suspect)

    Are you comfortable getting onto the roof of the RV and digging into an electrical device?

    Do you have a Clamp-On Ammeter?

    A Digital (or old Analog) Volt/Ohm Meter?

    If you have a meter, can it measure Capacitance (MicroFarads (maybe labeled uF")?