Dash A/C compressor clutch

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Dash A/C compressor clutch

August 09, 2017, 02:18:28 pm

My dash A/C quit putting out refrigerated air. I did a search of the subject which helped me in trouble shooting. What I have found is that the clutch is not engaging when A/C is requested. The fans on the condenser operate and the fan on the dash blower operates. The wire that feeds the clutch has about 5 volts to it. When A/C is no longer requested, the fans quit and the voltage to the clutch goes to zero.

My question, is five volts all that is needed for the clutch to engage or should it be closer to 12 volts? If it is supposed to be 12 volts, what may be causing the voltage drop before the clutch?

Re: Dash A/C compressor clutch

Reply #1 – August 09, 2017, 03:05:10 pm

Howdy Richard,
Sounds like you may be having issues with a troublesome 15amp/12vdc auto re-setting overload relay or lose/broken wire on overload. At least on my model year coach, this overload is located on the isolator board on front/driver side of engine compartment. On the attached print, the isolator and overloads are shown in the dotted box in the lower center.
Good Luck, Dave A

Re: Dash A/C compressor clutch

Reply #2 – August 09, 2017, 07:35:23 pm

Have you jumped the compressor and made sure you have enough Freon? Low pressure switch shuts the compressor off. I don't know if it could still let 5 volts through.

Re: Dash A/C compressor clutch

Reply #3 – August 09, 2017, 07:39:31 pm

For compressor clutch to be active, voltage from dash switch goes through both low & high pressure switches located on A/C hose in engine area. If refrigerant pressure is too low or too high, the clutch will be off. Temporarily jumping a pressure switch electrical contacts is a normal way to diagnose compressor clutch.
You may find refrigerant is low and the pressure switch is protecting your system. You may also have a failed inexpensive circuit breaker located on isolator panel.
Following your wiring diagram will be a big help. All components need 12+ volts. 5 volts indicates a high resistance connection somewhere, probably at breaker.

Re: Dash A/C compressor clutch

Reply #4 – August 10, 2017, 06:06:02 am

The wiring diagram for mine 91. shows the compressor gets power from battery terminal on starter that feeds a relay. Dash controls relay. Relay feeds compressor. Relay should be back there somewhere maybe under bed? Check your diagram and see if its the same.

Re: Dash A/C compressor clutch

Reply #5 – August 10, 2017, 12:52:44 pm

As a follow-up, I think I have solved the problem. Apparently it was merely a dirty electrical connector on the high pressure limit switch.

Per the wiring diagram, I located the 15amp circuit breaker and the relay where Dave said to look. I had power through the circuit breaker to the relay. There was no signal (power) to the switching terminal on the relay. I then went back to the pressure switches at the compressor. As a side note, contrary to the wiring diagram my coach has only a high pressure switch and not a low pressure switch. I pulled the connector from the pressure switch and determined that it had a positive voltage from the dash thermostat switch. Also there was continuity through the pressure switch so the pressure was within acceptable limits and the switch was working. When I plugged the connector back into the switch, the clutch engaged. Voila la !!! So I got out my contact cleaner and my dielectric grease and hopefully the problem is solved at zero cost. Time will tell.

Re: Dash A/C compressor clutch

Reply #6 – August 10, 2017, 04:13:59 pm

The low pressure switch is next to the condenser on mine. We have the same year.

Re: Dash A/C compressor clutch

Reply #7 – August 10, 2017, 08:13:43 pm

Thanks Chuck, I will check that out. That one probably needs cleaning too.

Re: Dash A/C compressor clutch

Reply #8 – August 11, 2017, 12:21:02 pm

Quote from: craneman – August 10, 2017, 04:13:59 pm

The low pressure switch is next to the condenser on mine. We have the same year.

Of course you were right Chuck. My low pressure switch is located beside the condenser and dryer. Thanks

Re: Dash A/C compressor clutch

Reply #9 – November 06, 2018, 05:42:14 pm

I am reviving this string of posts from a year ago.

With the help of several Forum members I was able to find and clean up the various components that make up the dash A/C system. At one point I thought I had solved the problem as the A/C began working. It worked for a while but then quit again. It was not high enough on the nuisance list to merit my attention and the coach was in storage most of the summer.

I finally got around to messing with it again. I checked for continuity across the high and low sensors, I applied 12 volts directly to the clutch (with the engine not running), and I checked for 12 volts across the 15 and 20 Amp fuses on the isolator board at the front of the engine room (where Dave Able said it would be, thanks Dave). I had decided that the compressor relay must be bad. As I was removing the relay I saw the short power wire from the relay to the 15 Amp fuse, which was hidden behind a mass of wires, was slightly loose at the fuse end. A little contact cleaner and a tweak with a wrench and voila the A/C is pumping out cool air again.

It really makes a guy feel good to solve a long term problem, especially at no cost. The first thing that came to mind when the compressor started spinning was the line from the movie when the drill sergeant said, "Gump, you're a GD genius."

As so many have said on the Forum before, if a 12 volt system is acting squirrelly, first check the ground wires then check for loose connections (even hard to see connections).

Re: Dash A/C compressor clutch

Reply #10 – November 07, 2018, 09:11:22 am

Rich could you do a picture of what you found. Thank you

Re: Dash A/C compressor clutch

Reply #11 – November 07, 2018, 05:26:56 pm

John, here are a couple of images of the dash A/C control board which (in my coach) is on the forward wall of the engine room, accessed under the bed. Please excuse the old insulation, I plan to replace it in the not too distant future.

Re: Dash A/C compressor clutch

Reply #12 – November 07, 2018, 05:36:35 pm

This is the second image.

Re: Dash A/C compressor clutch

Reply #13 – November 07, 2018, 05:43:23 pm

And, the location on Jan/Richard's coach is a LOT better than on earlier coaches where those relays were behind the driver's rear tire.

Yes, relocated by many of us to the "electrical compartment" at the foot of the bed where it is out of "harm's way".

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Dash A/C compressor clutch

August 09, 2017, 02:18:28 pm

Re: Dash A/C compressor clutch

Reply #1 – August 09, 2017, 03:05:10 pm

Re: Dash A/C compressor clutch

Reply #2 – August 09, 2017, 07:35:23 pm

Re: Dash A/C compressor clutch

Reply #3 – August 09, 2017, 07:39:31 pm

Re: Dash A/C compressor clutch

Reply #4 – August 10, 2017, 06:06:02 am

Re: Dash A/C compressor clutch

Reply #5 – August 10, 2017, 12:52:44 pm

Re: Dash A/C compressor clutch

Reply #6 – August 10, 2017, 04:13:59 pm

Re: Dash A/C compressor clutch

Reply #7 – August 10, 2017, 08:13:43 pm

Re: Dash A/C compressor clutch

Reply #8 – August 11, 2017, 12:21:02 pm

Re: Dash A/C compressor clutch

Reply #9 – November 06, 2018, 05:42:14 pm

Re: Dash A/C compressor clutch

Reply #10 – November 07, 2018, 09:11:22 am

Re: Dash A/C compressor clutch

Reply #11 – November 07, 2018, 05:26:56 pm

Re: Dash A/C compressor clutch

Reply #12 – November 07, 2018, 05:36:35 pm

Re: Dash A/C compressor clutch

Reply #13 – November 07, 2018, 05:43:23 pm

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