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Old 06-05-2018, 11:15 AM   #1
lucky_7
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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 mins...ac 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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Old 06-06-2018, 10:32 AM   #2
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Re: a/c symptoms, need help diagnosing issues

New symptoms over the last 2 days.

6/5/2018, Morning drive to work was fine, ac worked great. That afternoon the temp outside was around 90deg. Clutch never tried to engage.

6/6/2018, This morning the same, ac work great all the way to work, I will see if it does the same thing as yesterday this afternoon.
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Old 06-06-2018, 04:58 PM   #3
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So many choices of things to look at or try.....Where to begin?

Holy crap you could write a list of things to try at this point.

You could see when it's turned on but the compressor is off if there is any voltage going to the compressor and to the switches.

You could have die added to the coolant and start looking for leaks with UV light.

You could have it evacuated of refrigerant and then vacuumed with a pump and micrometer to see if it's got a leak.

You could jump the compressor to 12 volts to force it to run (if it won't seem to come on) and see what the pressures are doing.

My suggestion is evacuate the system and disassemble the orifice tube and look for contamination. I'd be willing to put money on it having debris in it. At that point the system needs flushing, new seals and reassembled and vacuumed (again with a vacuum pump and micro vacuum gauge).

I don't waste my time vacuuming any system without a micro vacuum gauge. To me it's a waste of time. With a micro gauge, if the vacuum gets below 500, you know there is no leak. A normal vacuum gauge will never tell you that.

Prior to disassembly, running the compressor will tell you if it's going to last or if it needs replacing.

In my 99's case I was having no problems ever but decided to change the compressor to a Sanden. When I pulled it apart the orifice tube had metal bits in it indicating the compressor was on it's way out.

Incidentally sometimes it's better to bite the bullet and find a REPUTABLE shop to go to. Particularly those jobs that require tools and equipment that the common lay person does not have. However I understand the frustration of finding a good shop. Luckily I have a neighbor that has a shop. If it doesn't need it, he wont do it.
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Old 06-07-2018, 09:14 AM   #4
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Re: a/c symptoms, need help diagnosing issues

Thanks for the advice. I took it to a shop and guess what, It never shut off. They said they ran it all day and drove it and the ac never shut off. So now what, I must have a leak...
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Old 06-07-2018, 12:22 PM   #5
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So be pro-active

First take it back and pay them to add die. Or do it yourself. Then use a cheap UV light to find the leak. If you don't see the leak pay them to use a sniffer to find it. Don't forget to put the sniffer in the vents inside in case the leak is occurring in the evaporator.

Second, the controls are NOT $300. I just bought one.

https://www.amazon.com/gp/offer-list...&condition=all

They used to be $40 now they're $100 +-
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Old 06-08-2018, 11:12 AM   #6
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Re: a/c symptoms, need help diagnosing issues

I couldnt find them on amazon last time I looked, thanks. Although it seems like that is not my problem. Over the last two day the system has worked flawlessly. I still think it is a leak somewhere so I will go get some dye and try to find it.
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Old 06-14-2018, 02:57 PM   #7
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Re: a/c symptoms, need help diagnosing issues

So I took apart the dash yesterday to see if the control might be bad. I had the truck running, ac on, and when I moved the connector the compressor kicked on. So I pushed it back in and the compressor kicked off. I did this a few more times to confirm, so now it definitely seems like my control is the problem. Ill get a new one and update when its installed.

FYI, the switch on the bottom of the compressor on the back is the high side switch, the one on the top is the cycling switch. We got a wiring diagram from gm and check the power at the switches to trace what was not getting power. It was the highside switch not receiving power from the control (A/C) button. That was led me to check the control.
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Old 06-14-2018, 03:32 PM   #8
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Re: a/c symptoms, need help diagnosing issues

Quote:
Originally Posted by lucky_7 View Post
So I took apart the dash yesterday to see if the control might be bad. I had the truck running, ac on, and when I moved the connector the compressor kicked on. So I pushed it back in and the compressor kicked off. I did this a few more times to confirm, so now it definitely seems like my control is the problem. Ill get a new one and update when its installed.

FYI, the switch on the bottom of the compressor on the back is the high side switch, the one on the top is the cycling switch. We got a wiring diagram from gm and check the power at the switches to trace what was not getting power. It was the highside switch not receiving power from the control (A/C) button. That was led me to check the control.
Thanks for posting up what you found. Will likely help someone else in the future.
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Old 06-14-2018, 06:28 PM   #9
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Re: a/c symptoms, need help diagnosing issues

http://67-72chevytrucks.com/vboard/s...d.php?t=762934
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Old 07-08-2018, 07:11 PM   #10
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Re: a/c symptoms, need help diagnosing issues

i rebuilt my ac on truck complete new parts.

first thing to check is the 2 shut down sensors

one is connected to the evap canister also known as accumulator , if i remember low pressure shut down switch.
other one is located on the ac compressor its self thats the high pressure shut down switch.


try those first u can by pass the low pressure switch by unplugging it and then connect a paper clip bend it to a u shape short the 2 terminals this by passes the low pressure switch circuit, see if ac pump engages, front magnetic fly wheel should spin.

dont run it this way to long just for tests to rule out a faulty low end pressure switch.

also check relays i think one relay behind glove box controls ac compressor power.

any disconnection of ac lines youll need to evap any refrigerant in there first, not good idea to vent this stuff into atmosphere but if u dont have the funds or option pressing on the low end fill and vent valve will discharge any refrigerant, and pressure in lines.

always replace o rings with new ones and dip them in pac ac oil.


other thing after this is to open ac line up at condenser located at front of truck, this is a big job thx to Chevy design as u need to remove front grille first.
think the 98 trucks chevy moved the connections inside engine bay area.

the top connection that slopes downward is the orifice tube, these foul up after number years and start to block coolant flow, replace with a new one if yours is black gummed up.

the orifice converts the refrigerant to a liquid to gas state in ac or its vice versa.

Last edited by diveplane; 07-08-2018 at 07:27 PM.
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Old 07-19-2018, 02:37 PM   #11
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Re: a/c symptoms, need help diagnosing issues

I ordered the controller from amazon. Hopefully that will fix this issue. The pigtail fix that Speedy posted seems like a good fix. I just dont have the time or the skill with a solder gun..
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Old 07-23-2018, 11:28 AM   #12
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Your just inviting more problems and more $$$$$

Don't be silly regarding soldering. If you don't know/want/care to solder them the old fashioned way with heat shrink tubing....Do it this way.

http://www.elecdirect.com/crimp-wire...k-16-14ga-25pk

You simply crimp them together like any other but splice and then heat it up and it solders the wire together and shrinks the sleeves without ever touching a solder iron.

https://www.amazon.com/Connectors-So...15854642&psc=1

If you don't replace the connections, it will eventually melt the new controller. As time goes by, they are getting more and more expensive. Next time will be even more $.
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Old 07-23-2018, 01:37 PM   #13
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Re: a/c symptoms, need help diagnosing issues

New controller was the fix, there is a crack in the trace that I didn't see before...here is a picture. Right in the radius of the traces on the big trace. You ask why I didn't jump the trace, well the clips on the control broke.
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Last edited by lucky_7; 07-23-2018 at 03:07 PM.
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