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The A/C on my dad's truck cuts in and out

Hello. i’ve listened to the Car Talk radio broadcast for some time now but i’ve been given a chance to use the website until now.

My dad recently asked me to find out what is wrong with his A/C unit on his truck. He has a Chevy Silverado 1500 LS. it’s a 2002 model. um… anyway, he usually blasts his A/C around 3 to 5. the a/c setting goes from 1 thru 5, and off. so i was thinking that since he uses the a/c so much that he’s gone and broken something.

I live in San Antonio and its the middle of summer so i suspect the heat has something to do with it. some days the a/c works, sometimes it doesn’t. although i’ve ridden in the truck a few times since the problem appeared, i’ve noticed that the a/c almost always works when we pull out of the garage or when its cool enough. and never works when we come out of a store or somewhere to the truck thats been left out in the heat in the parking lot.

There’s one more thing. i haven’t noticed it yet but this comes directly from my dad. he says that sometimes he’ll just be driving along and he’ll hear a ‘klunk’ noice and the a/c will start working again.

does anyone know how to fix this problem. i assume this is something very common. and would it be easy for me to fix? i know more about computers than i do cars, and i’ve already taken apart 1 laptop and fixed 2 others. i feel fairly confident taking part of a car apart… er, truck in this case.

It could be as simple as just adding some refrigerant. Auto parts stores sell small cylinders with a hose and gauge on it that lets you add some to the system. Very often it makes the AC work again for just under $20, providing there aren’t any leaks. If anything, it will let you check whether there’s enough refrigerant in the system.
Should you go this route, just follow the instructions.

but what of the ‘klunk’ noise? do you think that has anything to do with the a/c?
but still if there isn’t enough coolant, then why does it work sometimes and sometimes not?

The clunk is likely the AC clutch. There’s a sensor in the AC system that makes sure the clutch doesn’t engage when the pressure is too low or too high. Perhaps your pressure in on the hairy edge between being too low.
I had the same problem with our Integra last year.

You could bring it to an AC expert and have them diagnose and fix it. If they do a refill, it will likely cost you around $140 (in my area). No doubt they’'ll do a good job and it will work well.
On the other hand, gambling $20 by buying a refrigerant can that has a gauge so you can see whether the system is low and then add some may save you some money.

ok i’ll let my dad know, thanks a lot.

are there any specific products i should look for? maybe a good description of what to buy because we will surely get the wrong product.

Since it is a 2002, it takes R134 refrigerant.
This stuff, for instance: http://www.autozone.com/autozone/accessories/Quest-17-oz-of-R134a-and-2-oz-of-Sub-Zero-A-C-booster-with-shelf-saving-dispenser/_/N-261q?itemIdentifier=532242&_requestid=5228924

I see that^ one is a bit more than $20 but there are others out there (pepboys, harbor freight, advance, etc) and they mostly do the same thing.
First you unscrew the low pressure valve cover on the AC system. Look under the hood for two fittings that sit on top of aluminum hard lines. They are typically towards the top of everything, for easy access.
On my cars, the cover of interest is blue and just checked it is actually marked “L”. The high pressure cover is black on my cars, marked “H” - don’t mess with that one. The low pressure cover unscrews by hand. Don’t worry - nothing of the stuff will come out. It is just a cover.
You take that funny looking fitting at the end of the filler hose, you pull back a ring it has and slip it over the low pressure fitting of your car’s AC. It will only fit the low fitting.
On most of those things, you can measure the pressure and there’s an indication what’s low, normal or high. Just follow the directions on the can. When done, take the hose back off, put the cover on and try it.
Only add it if is considered low. Don’t overfill it. That’s equally bad.

If you find the level is okay, don’t add any but get it checked out by a pro. At least you tried fixing it and know it isn’t the level.

thank you very much, i’ll have my dad take a look at this.

ok so my dad went and got the recharger bottle or whatever and it didn’t work. the man at the shop said that it’s a bad compressor and that it needs to be replaced. any suggestions on how to do that? is there a guide i can follow. we still have the owner’s manual, is it in there?

The good news is that since you live in a hot area, the local A/C shops likely know what they are doing and can do the job quickly, and likely well for low cost. Ask your friends and neighbors for the name of a good shop.

I would avoid using a car dealer.   I believe that most often than not, having a good local independent shop will be cheaper, faster and less expensive,

Sorry the can didn’t fix it. It was worth a shot, though.

+1 with Joseph.
To replace a compressor is not a first time DYI job. You have to be able to (legally*) evacuate the refrigerant, replace the compressor, create a vacuum to get the moisture out and recharge it. That all requires special tools and a certain level of know how.
Get it done at an independent mechanic.

*legally, as one is not supposed to just open the hoses and let the stuff escape into the environment.

*legally, as one is not supposed to just open the hoses and let the stuff escape into the environment.

yeah i figured that, about the only work i’ve done on my dad’s truck is replace the oil filter and fix a broken headlamp (burnt bulb).

i’ll let him know. thanks very much.