Markmbaha1

Last week on a cool day the AC froze me. On a hot day the compressor cycled more off than on, I stayed hot. On a cool day i got it in the shop, firestone. Again the AC was freezing. The shop said the pressures were fine, but the high pressure was fluctuating. So they drew it down, checked for leaks, no leaks, refilled, I drove home cold. 1 week later yesterday it was in the upper 60s outside when I went for a ride. The AC froze me, compressor didn't cycle. Today it's about 78, it was sitting in hot sun and the compressor is cycling again just like last week on a warm day. Where ever I drove, the compressor cycled off more than on, again. I went to the shop from last week, talked to the same guy, he suggested I go to GM shop. My particular chevy cadillac GM shop tends to quote several hundred percent above other shops for their work, from personal experience.
Does anyone have a thought what may be causing this cycling only on hoter days? Thank you in advance.

CorvetteHeadz

What do you mean by "cycling"? Are you using the "Auto" feature? Just turn it on full blast AC and turn the AC **** down to 60 and make sure the passenger side is on full cold too.

Markmbaha1

The AC compressor cycles on to off, off to on...constantly. Yes its on 60 and passenger is all the way cold. But on cool days i cant leave it there, it does no cycke and starts to freeze me. Have to turn it up to 74. I always use Auto. Thats the purpose in having an Auto Climate Control aystem.

zz28zz

When it's hot outside, maybe the A/C high-side press fluctuates too high and compressor gets shut off?

If you don't have a set of gauges, I'd take it somewhere to have the press checked when it's hot and cycling.

CorvetteHeadz

Ahhh. Ive owned my C5 23 years. Never used Auto once. I control temp with the fan. Hot - fan higher. Cold - fan lower. Much easier.

Markmbaha1

Interesting ive never not used auto. I dont think about it i dont touch it. I dont touch any buttons, thats the beauty. It comes on all pre set when i start the car and it does everything for me. Adjust the fan speed and temperature without touching.

Markmbaha1

That is what Firestone told me, the high was fluctuating. But it was a cool day when it was running properly, no cycling.
What would cause the high side perssure to fluctuate while the compressor was always engaged? This may be the problem. Next shop is a dealer or specialty shop. I can't keep paying people $200.00 to find no leaks, draw down and recharge. Seems like some part is sporadically failing. Thank you.

bookyoh

Without pressure readings to see if your system is cycling on the high side pressure readings and seeing how low the low side pressure is running, I can only give you a couple of possibilities.
1. If you have the OEM compressor, or an OEM copy, there is a control valve that regulates the pumping capacity of the compressor. If that valve fails to reduce the capacity, the compressor will pump as if it is a fixed displacement compressor. The compressor could then cycle off the high side pressure.
2. Your system is significantly over charged and running at much higher high side pressure.
3. Your system has a relatively high percent of air contamination from either a poor evacuation or a faulty refrigerant recovery/charge machine.
4. You have a faulty high side pressure sensor or a wiring issue with that sensor.

Without data, these are all just possibilities.

CorvetteHeadz

I would find a Corvette specialty shop in your area ie someone who knows about these cars and their quirks. Firestone is for old pick up trucks and 1998 Civics.

benflynn

this

Markmbaha1

Thank you, I live at a tourist beach not many speciality shops of any kind, but I'll do some digging. Probably end up at the Chevy Cadillac dealer. Thank you.

CorvetteHeadz

contact your local corvette club or find a local Facebook page and get a referral.

zz28zz

Would need to see the fluctuation frequency and amplitude. Could be a long slow rate fluctuations with large pressure changes or could be rapid 10 psi fluctuations. Rapid needle jumping would indicate a compressor issue most likely. A long slow rise and fall would either be contamination/water effecting flow thru the orfice tube or cooling fan/air flow issues (at the condenser).

benflynn

Sure seems overcharged to me.

zz28zz

Hopefully they're charging the system by weight and not the gauges.

Markmbaha1

Two times in the last 4 starts, I've heard a brief sound like a high pressure valve spraying out pressure. Its very brief. Could that be the AC system? They consulted me about weight on evac and fill last year, the same 2 weekends ago.

CorvetteHeadz

take it to a corvette shop!

bookyoh

That sound may be your compressor releasing pressure from the high pressure relief valve which is located in the rear of the compressor. For that to happen on a/c start up would require a significant amount of overcharge. Did your invoice from Firestone state how many pounds or ounces of R134a they charged you for? R134a has gone up in price in recent years so I would think they would want to charge you for every ounce they put in. If stated in the invoice, it should in the 26 to 28 ounce range.

It is not good to run your a/c if your system is overcharged to the point where it vents R134a. It means you are subjecting your compressor to pressure and internal loads far beyond normal running conditions.

A reputable shop that services and repairs a/c should be able to diagnose far better than any of us responding to your thread.

Markmbaha1

I've got an appointment tomorrow morning with a shop that is reccomended by the local corvette shop.

Markmbaha1

I'll check the invoice for ounces tomorrow on my way into that shop. Thank you. A lb of freon is 16oz correct?