Truck A/C works intermittent

[amboy49]

The a/c on my 1996 Chevy Z71, with a 350 engine, works only intermittently. It has 96,000 miles on it. The a/c will come on and blast cold air for awhile and then suddenly quit. I took it to a local shop today and they said it needed refrigerant, added some, and charged me $60. I drove it for about 1/2 an hour this evening and once again, started out nice and cold, and then suddenly quit working.

Obviously it’s not a refrigerant issue since the shop just added some. I’m not sure the condenser clutch is functioning properly. Since YouTube is everyone’s friend I did a quick search. One video identified a low side pressure switch as a possible problem. I can’t rule out an electrical problem, but since it works great for awhile I’m thinking that’s far down the list of potential problems. I don’t know what makes the clutch work for certain, but it doesn’t seem to be turning when the system should be calling for a/c.

Hoping for some some suggestions about where to start or what to consider. I do plan on going back to the repair shop but based on their initial failures to repair the problem I’m not confident they can diagnose the problem.

Thanks in advance

 

[thunderchicken]

A cycling switch or pressure switch could be the culprit. Based on it functions for a while a couple things I would look for are ..is the relay working properly and there could be a restriction in the system. A few things can cause it but it's possible the evaporator is icing over as well.

 

[JeepHammer]

In my limited experience, but knowing GM had real issues with pressure cycling switches throughout the 90s, I believe I would go that direction also.
There is a Schrader valve under the switches, so you can change them without loosing all your coolant.

The late 80s and all through the 90s GM had a problem with low pressure cycling switches in particular.
If the compressor cycles on and off quickly when at idle, it's almost always a low pressure switch fail.
GM makes a real snapping sound when the compressor cycles, and it's a fast snapping when the low pressure switch fails in those particular vehicle.

 

[churchmouse]

I agree with the Pressure switch being the culprit here. There is nothing else in the system on your truck (to my knowledge) that would make this happen unless the A/C dash controller is the culprit. These were also known to have issues.

Due to its age I can see it being a bit low on refrigerant. To a tech hanging a gauge on it that would be the starting point.

 

[sugarcreekbrass]

Does it go out while driving, or while stopped? My 02 Dodge has had a leak for a while, but this year I couldn't get it to work at all. I took it to a shop and I had some blockage in my line. I forgot what he replaced, but got it to work. He then realized my fan wasn't working so my A/C works as long as I am moving. Stop and go in town, it doesn't.

 

[Jeepfanatic]

Does it go out while driving, or while stopped? My 02 Dodge has had a leak for a while, but this year I couldn't get it to work at all. I took it to a shop and I had some blockage in my line. I forgot what he replaced, but got it to work. He then realized my fan wasn't working so my A/C works as long as I am moving. Stop and go in town, it doesn't.

Does the fan blow on high or not at all?

 

[Cameramonkey]

I agree with the Pressure switch being the culprit here. There is nothing else in the system on your truck (to my knowledge) that would make this happen unless the A/C dash controller is the culprit. These were also known to have issues.

Due to its age I can see it being a bit low on refrigerant. To a tech hanging a gauge on it that would be the starting point.

this would be my first check. If the system was low/empty the factory Freon had to go somewhere. If it’s a true leak, your new Freon could have taken the same path.

 

[amboy49]

Drove the truck again today. Started off as before with the a/c blowing cold. After about half an hour of stop and go driving the blower was working but no cold air. I raised the hood and noticed the compressor clutch wasn’t turning. I felt the low side side pressure switch (valve) was very hot to the touch. NAPA said a replacement is $75. It looks like a pretty simple swap from the You Tube video I watched. I may give that a try since the wizard at the shop I had gone to said they couldn’t look at it until next Monday.

 

[4651feeder]

Drove the truck again today. Started off as before with the a/c blowing cold. After about half an hour of stop and go driving the blower was working but no cold air. I raised the hood and noticed the compressor clutch wasn’t turning. I felt the low side side pressure switch (valve) was very hot to the touch. NAPA said a replacement is $75. It looks like a pretty simple swap from the You Tube video I watched. I may give that a try since the wizard at the shop I had gone to said they couldn’t look at it until next Monday.

With that condition present did you attempt to jumper the low side switch terminals?

 

[maxwelhse]

My Dad has had 4 of those relays go out on his '95 since new so I'm inclined to agree with the others about that being your problem. About 50% of the time you can just smack it with a screw driver handle and it will take off again.

If it IS actually losing refrigerant (which sounds unlikely, but possible), I suggest replacing the charging ports. I actually just made a quick video on this topic and my Blazer is exactly the same configuration as your truck. I had to do exactly that repair on my Dad's truck last year... It was about $15, plus refrigerant charge.

https://youtu.be/3whKGegFkPI

 

[HoughMade]

If it's cold one day, then blows warm, and the next time you drive it, it blows cold again- it's not the refrigerant.

If it starts cold, goes warm and stays war, never get's cold again, it could​ be the refrigerant.

 

[sugarcreekbrass]

Does the fan blow on high or not at all?

Sorry, I didn't mean the blower fan. He said it was the condenser fan. I have had the resistor go out twice in the past, fan only works on high.

 

[Jeepfanatic]

Sorry, I didn't mean the blower fan. He said it was the condenser fan. I have had the resistor go out twice in the past, fan only works on high.

Common problem on them. If you need help with parts shoot me a PM

 

[Clay Pigeon]

Drove the truck again today. Started off as before with the a/c blowing cold. After about half an hour of stop and go driving the blower was working but no cold air. I raised the hood and noticed the compressor clutch wasn’t turning. I felt the low side side pressure switch (valve) was very hot to the touch. NAPA said a replacement is $75. It looks like a pretty simple swap from the You Tube video I watched. I may give that a try since the wizard at the shop I had gone to said they couldn’t look at it until next Monday.

I believe Napa is pumping you alittle hard, That switch normally is about 20 to 33 bucks.
Stop in at OReilly's, Advance or the Zone and price it.

 

[Bennettjh]

My Dad's '94 K1500 has that problem. Changed the switch a couple times. Even made me a handy little jumper for it.

 

[hoosierdoc]

Maybe compressor works, gets hot, some parts stick, it stops working, cools down, works again?