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Old 06-05-2018, 11:15 AM   #1
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lucky_7's Avatar
Join Date: Mar 2013
Location: Muskogee, Ok.
Posts: 119
a/c symptoms, need help diagnosing issues

Hello Everyone,

Slightly long post....I have a 97 gmc 1500 5.7L. It has an ac problem that started late last year and I now have the time and the excuse to fix it, Its hot in Oklahoma...

When this all started I thought it was the control in the cab, and it still maybe be. I have done some diagnosing and try to list them as good as I can.

1. Last year, ac worked great, then one day it shut off driving. The next morning it worked fine. Then it started getting very inconsistent. I could turn it off and it would cycle back on, then off again. Some days it would work all day, some days it wouldn't this led me to believe it was the control, and they run about 300 so I pinned it for this spring. I did try the ac relay under the hood and it didn't change anything.

2. 6/2/18, I got a can of ac pro with leak seal, I figured if I had a gauge and I could maybe tell if it was low that would be my problem. Sure enough the freon was low, so I added around 16oz. Nothing... I thought the pressure switches might be bad. So I jumped the plugs after testing them for a good voltage and nothing. I took about an hour to look over the web for any other causes, went back to the truck and jumped the low side switch and the compressor started to cycle. At this point I added more freon until the comp. was more consistent and the air got cold. Everything worked great, until I tried to roll up my windows and the clutch disengaged, and never cycled back on.

3. 6/4/18, I took the truck to a mechanic friend of mine, he put gauges on the truck and it still read a little low, so we added 12 more oz of freon and it seemed like everything was working, until I tried to roll up my windows and it cycled off. I know, its weird. The comp. never cycled back on. So I waited about 2 hours and tried it again. Same symptom, ac cold, cycled off and on once, tried to roll up my window, cycled off and never came back on. At this point Im thinking its a voltage drop thats kicking out the coil, checked batt and it had 14 volts, check coil plug and no voltage. So the system is in fact kicking off the coil for some reason.

I leave work and out of curiosity I crank the ac and drive to the gym, I sat in the parking lot on a 90 deg day and let this thing run for 25 mins and it never shuts off...Ice cold air and I can hardly stand to stay in the truck. I work out for about and hour and half. Jump back in the truck and crank the ac again, drove another 15 mins across town and sat in the truck for another 5 was cold and never shut off.

6/5/2018 This morning it was the same, I drove to work and the ac was cold all the way, never shut off.

I wondering now if I might have a leak and the highside switch was cycling the comp. Now since it has leaked some its more normal and could be working fine until I lose enough it starts to cycle from the low side switch.

Let me know your thoughts...

Last edited by lucky_7; 06-05-2018 at 03:55 PM.
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