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Hi all,
Working on my 1990 base vette, no idea what the condition of the AC system is/was other than it's low on r134 now. The fittings are definitely converted, don't know about anything else.
Oh, and it's the auto climate, C68.
Anyway, what I have right now is this: I charge the low side up to 40ish or so and the compressor kicks on. The pressure drops down below 20, compressor kicks off. It runs about 6 cycles before the mode button flashes on the hvac controller and the low pressure code sets. After that I have to cycle battery power to do any more with it.
At about 50 psi low side (outside temp around 90), the high side is going up to the low 100's - not quite 150. My instinct is to add some more until the low side stops dropping below 20ish, but I'm just not sure how high I should think about going with the low side pressure (or weight of R134) to do that. Not experienced with AC systems at all.
What steps should I take next, or is there already signs of trouble?
Last edited by RescueVette; Jun 7, 2022 at 06:32 PM.
Reason: add note for C68 option
Adding Freon is a judgment call along with experience. Hard to give you an exact answer. If the system was empty then you know how much to put in and I don't exactly remember but these cars take about two 12 oz cans. I don't know how much you have already put in but one full 12 oz can is in the ball park.
I touch the pipes, see how fast is get cold from start up and see how much it cycles. On high fan it should hardly cycle at idle or not at all. On low fan it should definitely cycle a few times a minute. And it should not be icing up at any time. It should cycle 23 to 46 on the low pressure side but I don’t know if the cycling switch was changed for 134 so cycling might be a couple pounds higher. Of course increasing RPM may be necessary to get it to cycle depending on fan speed.
Personal quick "rule of thumb" with average humidity
--low side is about 30PSI --1200-1500 RPM--
--high sid--take ambient temperature and add 100--
remember "quick and dirty--rule of thumb" only
From the info stated, appears low on freon charge
Measure the low side pressure with the can turned "off", not when you are injected freon into the system. The pressure will change as the compressor runs or shuts off, but you want to measure the system pressure without measuring the "can" pressure. You should have ~45lbs. when it's full. If the compressor is cycling on and off and you have to keep resetting the code, your system is low on freon. If it was totally empty, to fill it you probably need at least 2 1/2 cans of 12 oz. each, or about 2 lbs, of freon.
I have a question . . . and by all means I'm not trying to take over a thread here.
Does anyone else experience your engine bog or stutter when your AC is on? This is at idle or driving.
Yes, this is normal. It takes a lot of HP to turn that compressor. I'm not sure the exact number on ours, but somewhere between 5 and 10 is normal on most compressors.
When I had an 02 golf with the 180 hp turbo engine, starting it in first gear was an ordeal! That thing made almost no power without the turbo and it was very, very easy to stall if the AC was on.
I have a question . . . and by all means I'm not trying to take over a thread here.
Does anyone else experience your engine bog or stutter when your AC is on? This is at idle or driving.
There can be lots of reasons.
I'm assuming you have a 92. Always state you year starting a thread. On my 94 there is no real reaction to engaging the A/C compressor other than a click. Here are some suggestions.
IAC not working
ECM driving the IAC is not driving it.
Vacuum leak
A bad spark plug or cylinder not performing correctly.
Leaking EGR valve
Yes, this is normal. It takes a lot of HP to turn that compressor. I'm not sure the exact number on ours, but somewhere between 5 and 10 is normal on most compressors.
When I had an 02 golf with the 180 hp turbo engine, starting it in first gear was an ordeal! That thing made almost no power without the turbo and it was very, very easy to stall if the AC was on.
I know AC can rob some horsepower.
Originally Posted by pcolt94
There can be lots of reasons.
I'm assuming you have a 92. Always state you year starting a thread. On my 94 there is no real reaction to engaging the A/C compressor other than a click. Here are some suggestions.
IAC not working
ECM driving the IAC is not driving it.
Vacuum leak
A bad spark plug or cylinder not performing correctly.
Leaking EGR valve
Well technically it wasn't my thread
But yes my car is a 1992. Thank you for the input, I like hearing possible root causes. I know my AC doesn't blow cold anymore. I literally only turn it on in town traffic to kick the electric fans on lol.
A/C system charging
