Intermittent failure of A/C to engage
 

Hey folks,

Out of the blue my A/C stopped blowing cold, then kicked on again -- I was thinking either a slipping belt (which looks fine -- car has only 27K on it) or a failing compressor or compressor clutch.

Unfortunately, I am out of warranty.

A search suggests that the clutch can fail, although I also saw a few threads where posters claimed that low pressure in the system can cause the compressor to go on and off (which is news to me).

Other symptoms include a slight bounce on the idle -- probably due to A/C compressor engaging then disengaging.

Thoughts on this?

Also, in the even that I need a new compressor or clutch assembly, anybody who has tossed theirs, please shoot me a PM.

Any chance you have Stillen Gen 3 intakes? If so and you didn't protect the ac line on the driver's side the intake tube may have started to rub through it causing a refrigerant leak and therefor a low pressure causing the ac to act odd.

^^^ Nope -- OEM airboxes.

One other symptom that makes me think it's the compressor -- car feels intermittently draggy and the idle is up several hundred RPM than normal for the A/C.

My guess is, that means the compressor isn't turning smoothly, and so the car is working harder to keep it running.

ARGHHHHHH! :icon14:

Bump?

A good buddy of mine said it might be linked to my fans failing???

Apparently a problem on last gen Z's was that the fans would cycle on and off and this disrupted the A/C? :confused:

Anybody have any other ideas?

Also, again, if anyone has an A/C compressor they want to sell, let me know.

Ooooookay... well, no one has checked in, but here is an update:

Problem has NOT resurfaced. I'm thinking it was just a fluke of slightly high A/C pressure+high FL heat+low speeds for an extended period of time.

But, an oddity has occurred that I can't imagine is unrelated: Know how when you turn off the car and turn it back on, the A/C always automatically comes on (some folks complained about that)? -- well mine doesn't anymore.

If I leave it off, but fan blowing (vent) turn the car off and then start the car again, it stays off :confused:

I'm thinking there must be a specific relay or fuse associated with this... anyone have any ideas?

Also, for those of you who would rather it not come on automatically, well this might be the fix... :p

If it only happens when it is hot outside and/or you are moving slowly, then it may be kicking out on high head pressure. This could be caused by a fan(s) problem - burnt motor, damaged fan, fan not going to high speed, &. I'd verify fan operation first. If the fans are OK, I'd check pressure - you may have too much "Freon" in the system (not likely, but you never know).

Since it has "fixed" itself, low pressure is not likely.

I'll take a look at the FSM and see if I can find anything that fits your symptoms.

Edit: Whoa! A lot more complicated than I thought it would be. It even looks at Intake Air Temperature. Read through the HAC section of the FSM and see if you can spot the problem. Maybe we can answer specific questions.

Another thing I'd check is the connector at the refrigerant pressure sensor.
Edit 2: And the connector on the ECV (Electrical Control Valve)

I'll look into it and report back.

My other theory was that somehow tuning the uprev fan duty cycle by air temp but leaving the A/C related table alone caused some sort of weird ECU error, but the apparent change in the auto on feature is very weird.

Radiator fans still work fine snd kick on and off with A/C coming on, no running even a little hot, and the A/C fans seem to work fine too.

Will have to check service manual for range of normal Freon pressure -- apparently that can be logged through cypher.

What about the auto on feature? Is that fuse related?

If you can monitor them, check the signals going to the clutch and the ECV. If those look normal, then you may have a bad clutch.

As for the auto feature problem, I just can't tell. :( I'll take another look at the FSM later and maybe I'll have a eureka moment.

Since no body else seems to have any suggestions and I don't have a real good grasp on how the HVAC is controlled, you may be better off taking it to a dealer and letting them troubleshoot with CONSULT.

With the hood open is the ac fan turning when ac is on?

I had a problem on another car whereby the ac would behave similar. Turner out to be the fan was weak. It would only run if I helped turn the fan by hand . changed fan and problem sorted.

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^^^ fan turns on and has only happened one other time -- same thing, prolonged low speed driving on a blazing hot day.

I finally logged A/C pressure with Cipher -- was usually around 2.0, but occasionally spiked up to nearly 2.6. Anybody know what is considered "too high"?

Ooookay -- well, apparently 4.5 is high, and, so I'm told, entirely due to an ECU glitch that results in it being replaced along with several A/C sensors.

So now I have no clue why my A/C was acting crazy.

Also, now I have a slight intermittent stumble in my idle... I may be chasing semi-random electrical gremlins...