AC compressor on and off and on and off

[baalamb20]

Hey mine was doing that too along time a go,off on off on especially on hot days and then it stopped completely, some idiot mechanic told me it was low on gas and that my compressor was stuffed he didn't even check it, told me about $1100 to fix and that included regassing and new compressor I told him no thanks, anyway I took it to a automechanic and it turns out its that little switch behind the front grill he called a low pressure switch, he replaced it and it's been right as rain ever since ))

 

[DJ_Cosmic_Fire]

Be Cool

Hi vpcomm92,

This is a common issue with our cars, so unless you’re in a good mood & have decent audio to boot, it can be quiet irritating, I switch A/C off when the need for rapid speed is required... I put new ECU in 2years ago & have replaced low pressure switch, TX valve, re-gassed system, UV dye in compressor oil to check system for leaks, new O ring, vac test - all OK – cabin temp can get as low as 6 degrees – still works great! :spot on:

The compressor clutch engages at short intervals (every minute or so) & excessive wear of the compressor is the root cause - ECU controls the frequency of A/C compressor to balance power load, so the solution is to bite the bullet & get a Genuine Sanden Compressor (AC 102G), do your research in your local area for a decent Auto Electrician - A/C workshop to fit & test properly with warranty.:idea3:

 

[MikeC]

I just had this problem- AC compressor short cycling - I had gas added for summer. The short cycling was noticeable when I got back from a 2 hour drive. Opinion on the web was that overgassing may cause this problem so I then bled gas out - the short cycling problem didn't stop so after a long drive with no improvement I disconnected the LP switch on the accumulator- to see if it was feeding a LP cut out signal to the ECM and the short cycling stopped. I then reconnected the LP switch and the shortcycling stayed stopped.
All I can think of is that dirty contacts or a sticking LP switch caused the ECM to think the system was low on gas. Anyway I'm posting this to let people know that these 25-30 year old LP switch assemblies can cause AC compressor short cycling.

 

[HarryHoudini]

Be Cool


The compressor clutch engages at short intervals (every minute or so) & excessive wear of the compressor is the root cause - ECU controls the frequency of A/C compressor to balance power load, so the solution is to bite the bullet & get a Genuine Sanden Compressor (AC 102G), do your research in your local area for a decent Auto Electrician - A/C workshop to fit & test properly with warranty.:idea3:

Yes,good place to start if the Condensor is not leaking.I fitted a new Compressor to my Vn wagon but still had problems,local Air Con Guy said its probably the Evaporator and major job $ wise as the dash has to come out.
That was 5 years ago and still haven't done it but will get around to it one day as i rarely drive car these days but hate the air con(and anything else) not working.

 

[VPRob]

Yes,good place to start if the Condensor is not leaking.I fitted a new Compressor to my Vn wagon but still had problems,local Air Con Guy said its probably the Evaporator and major job $ wise as the dash has to come out.
That was 5 years ago and still haven't done it but will get around to it one day as i rarely drive car these days but hate the air con(and anything else) not working.

Hi Harry, how does the aircon guy diagnose the evaporator? Is the system losing gas? If so the 0 rings between the engine bay pipes and the evaporator inlet pipes are replaced from under the plenum and NOT by removing the dash. There are no other connections between the plenum cover and the body of the evaporator. If those 0 rings are leaking it will be leaking onto the cabin side of the firewall and so the leak will be hidden, usually behind the noise deadening insulation on the inside of the firewall. I did replace my evaporator because I had the dash out (for the one and only time - never again) but the old evaporator looked a pretty rugged unit and may well have been ok. Worth checking your 0 rings before going down the dash out route. It might be a much cheaper fix than you are expecting and, I agree, no aircon is a pain!

 

[MikeC]

Over the years I've had everything accessible tested with the freon sniffer and green dye- no leaks in the engine bay so I only have the evaporator and it's pipework left for the leak. It's good to know the evaporator is robust because they're no longer available new - even from people that still have them in their catalogues.
So the only connections to the evaporator core are the two on the left hand side of the plenum below the wipers with the socket head bolt? That's good news, I might just have a loose socket head bolt-allan key fix- my full gas charge lasts about 3-4 months.
Thanks for the advice.

 

[HarryHoudini]

Hi Harry, how does the aircon guy diagnose the evaporator?

Hi Rob...not sure but that was the only component left as we fitted another condenser just in case.It was low on gas but topping up didn't help.
Aircon guy wasn't very enthusiastic about fixing,he seemed to think the system was full of 'shiit/muck ' from the old compressor failing and said with a new evaporator and with a full system flush and "i might be lucky" .
Anyway no expert on all this just thought i would throw my experience in.

 

[MikeC]

"how does the aircon guy diagnose the evaporator " I had the AC guy try his freon sniffer in the evaporator pan drain hose but it sensed nothing.

 

[HarryHoudini]

"how does the aircon guy diagnose the evaporator " I had the AC guy try his freon sniffer in the evaporator pan drain hose but it sensed nothing.

Don't know,with mine that was the only thing left after the Condensor and new Compressor but he seemed to know what he was talking about as he said removing the dash is a bugger of a job.

 

[MikeC]

Don't know,with mine that was the only thing left after the Condensor and new Compressor but he seemed to know what he was talking about as he said removing the dash is a bugger of a job.

The O rings under the plate that Rob mentioned are worth a look. An engine bay freon check would miss them because they are away from the other AC components.
I've paid to have the car regassed each year because replacing the evaporator is such a crappy, expensive job.