Intermittent Air Conditioning - AC Problem

[Jesda]

73 degrees today! Whee!

Normally I prefer the roof and windows open but I wanted to see if my AC was working. I started the car and idled in the driveway for 10 minutes, letting it warm up to operating temp, and it was blowing warm air.

I went for a drive and it would come on and blow cold and then suddenly go back to blowing warm air, back and forth, at random.

I shut the car off, tried turning the compressor by hand, and there was some resistance, as there should be, but it turned. All the belts are new and appropriately tight.

Checked the AC fuse, and its okay.

Last year I did:High pressure radiator/fan switch thingyReplace CompressorFlush/Recharge with R12Replace Receiver/DrierBelt and PulleyClean out evaporator fins

I took it to the local Firestone, and they said they wouldnt have the testing equipment ready until mid-April. On a hunch, he said perhaps its low on R12, and thats causing the system to automatically shut down when pressure is too low.

Any hunches would be appreciated. Thanks in advance!!

[elwesso]

The AC cycles on and off to maintain correct temp..

Did you try turning the temp way down for it to stay on?

[Jesda]

Yeah, I set it at 65 when the ambient read 85 and it blew warm. Sometimes it blew ice cold for a few minutes, then it would go back to luke warm for 20 minutes.

[DAEDALUS]

On a hunch, he said perhaps its low on R12, and thats causing the system to automatically shut down when pressure is too low.

That was my guess too. It's right near borderline with the pressure switch, and the compressor engaging drops pressure, then after it shuts off the pressure rises.

I would tap into the pressure switch line with a voltmeter and see if the steps in voltage coincide with the compressor turning on and off. If so, then either pressure is low or switch is bad.

[qship96]

The AC cycles on and off to maintain correct temp..

Did you try turning the temp way down for it to stay on?

A/c does NOT cycle on and off on the q45! with system set to auto,compressor stays on full time,unlike many other cars.vent temp. and fan speed vary to maintain temp,but compressor stays on full time,does not cycle like some other systems!

[elwesso]

Not true.. WHEN ITS COOLER, I hear mine cycling on and off, and my AC is known to work perfect, as it was redone.....

It is a variable displacement and when its warm enough, you are right... But I konw that Ive heard mine turn on and off when its say below 60..

Generally during the winter I keep it on ECON unless the windows get foggy...

[qship96]

compressor ALWAYS runs when in auto mode unless ambient temp drops to near freezing in the q45,if yours is cycling at anywhere near 60 degrees,IT is not working perfectly,or as Infiniti designed,peroid!

[DAEDALUS]

Per the manual, the clutch may shut off if ambient is 45* or lower, depending on several factors. It will shut off at 19* no matter what. It's a known problem, at least with earlier models, that ambient temp, as registered by the HVAC controller, can be off a fair amount at first start. If the ambient is showing 46* or higher, the compressor should turn on if the AC is on.

[Q45tech]

Old flex hoses and o-rings to compressor can leak [permeablity] with age especially with R12.R12 only gauge sets are cheap as obsolete.

I end up adding ~~3 ounces per year of R12 to maintain 2.4 pounds of charge ~~~7-9% annual leakage.........why we now use R134a it loses only 1 ounce per year.........better by 3 times.

Just part of $3,000 annual M&R. [correct for inflation]

[Mr.Q45a]

Hi Jesda

I'm experiencing the same problem you describe in this post . the posts that followed discuss when the compressor runs and give suggestions to check the pressure switch .

But no place can I find a definitive answer to our similar problem .

How did you rectify the intermittent air conditioning ?

please be as detailed as possible.

Best regards,

Quash

[CrimsonQ]

i had the sdame prob with my 94 cougar, not that these cars at all any close to the same but ive worked in hvac for many years and every system runs along the basic principles. that being said my problem was the pressure switch, check that first and if all else fails, replace it and charge the system

[Jesda]

I had my high pressure switch replaced two years ago along with the compressor and receiver, but the low pressure switch is still original, which could be a culprit.

Temps dropped lately so I haven't had much motivation to have it checked out. Plus there's Mother's Day expenses around the corner.

I will update when I do.

[DAEDALUS]

It's a single switch--"dual-pressure switch".

[Jesda]

Good info! In that case, there must be a minor leak somewhere.