[Chester Stone]

A few years ago my thermostats bit the dust and I installed new ones acquired from Newell.  I admit that their schematic left a lot to be desired.  I have been curious for some time that my rear A/C system does nothing when set to low fan.  However it seems to cool fine when set to high fan (two compressors).  I finally got around to checking the amps going to all four A/C capacitors.  All four have 124 volts available to the control board, but the incoming amps for the rear number one compressor only draws 8 amps while all of the other three draw about 11 amps.  The draw going from the control board to the number one capacitor is only 4 amps while all of the other draw about 10 amps.  I am embarking on the installation of high capacity relays, and want to be sure everything is operating OK.  Any suggestions as to what might be wrong would be welcome.

[bikestuff]

Chester,

As you have figured out...the logic for the compressors comes from the thermostat.  It could be a faulty thermostat or broken wires or something wrong with the compressor itself.  There are also some relays on the board that could be bad.

As a way to split the problem, can you check the wires from the thermostat (where they attach to board)?  I'm going to guess that the control voltage is 12VDC.  I would just pull the control wire connector and use a paperclip to probe the end of connector.

   

Cheers!

[Chester Stone]

Thanks Bill. Tomorrow I am going to check the thermostat wiring to be sure that I connected the new but different thermostat. Not sure what you are referring to re the control wire connector.

[bikestuff]

The thermostat wire goes from the thermostat to that connector in the middle of the AC control board. (See the picture). That is what I called the control wire connector. It simply unplugs from the control board.

You should see the same wires at the thermostat and at the AC control board.

According to the picture Yellow and Orange wires control the Compressor 1 and Compressor 2 respectively.

[Richard]

Hang on.

You said the number one compressor is drawing four amps, and all the other compressors draw ten amps. Is it safe to assume you are using a clamp on ammeter on the wires going to the compressor?

If so, the problem is likely low or no charge in compressor one loop. Nothing for the compressor to compress, therefore no load.

If it were a thermostat or relay problem, you wouldn't pull any amperage on the compressor wires to number one.

If you still suspect a wiring issue, pull the compressor connections for one and two from the board and swap them. Does the problem stay with the position on the board or does it follow the compressor?

[bikestuff]

Yes, what Richard said.

[folivier]

Listen to Richard. I always like to eliminate the simple stuff first. It's real easy to make a simple problem more difficult by over-thinking it.

[Chester Stone]

Interesting results from switching. For future reference, you cannot switch the connectors that connect between the control panel and the capacitors because one is female and one male. I had to cut and splice using bullet connectors.

Before the switch, nothing ran with the thermostat set on low, but on high, compressor one drew 4.5 amps and number two drew 7.2 amps. After the switch, and on low, compressor one drew 7.7 amps, compressor two drew 0.0 amps and the fan ran on low speed. When set to high, the fan ran faster, as it should, and compressor one drew 7.5 amps and compressor two 4.3 to 4.7 amps. If I am not mistaken, which I frequently am, both compressor work correctly when switched, thus the problem may be in the thermostat, but more likely in the control panel. Please comment. I think I will leave them reversed when I next install the heavy duty relays.

The outside temp was 77, inside the coach was 61 after about 30 minutes running the back air and the temp of the air from the A/C was 58 degrees. I do not necessarily trust these readings.

[Richard]

Chester,

Can you clarify? When you say compressor 1 are you referring to the physical compressor, or the position on the circuit board?

[Chester Stone]

Richard, my A/C schematic, as well as those if have copied from the forum, show the connectors in the upper section of the control board as Compressor No. 1. The wires are white and black. I should point out that when Newell sent me new thermostats a few years ago, one was RVComfort model 6635A336 and the other model 6536A3351, but they both look alike. Sometime today or tomorrow I am going to recheck the thermostat wiring on the rear thermostat. Irrespective, even if it is wired backwards, I cannot explain why only 4 amps in that control board circuit to either of the compressors.