My AC Isn't Working!

[HammerDown]

Ok, so as I recal reguardless where the vent selector was I always had to push the AC-dash button...AC never automatically came on when I moved the lever to "defrost", I still had to press the blue AC dash button.
Stopped by my AC guys shop and he said, either the pressure switch is protecting the system from freezing up by not allow the clutch to engage OR, the system may be a little low on Freon. Or, the AC clutch may be shot...but doubtful.
As I do recal the ac was short cycling a bit towards the end of last summer.

 

[Koch13351]

Short cycling is a sign of low freon. My '84 was cycling 1 second on 3 seconds off until I added more freon.
Now don't quote me on this, as I'm not 100% sure on its truth:
I've been told that when you do a R-12 to R-134 conversion, you can just change the fittings and it will work, but the R-134 will very slowly bleed out of the R-12 hoses since it's a smaller molecule. So a complete conversion would include R-134 rated hoses.
Maybe a little shot of freon will fix your problem?

 

[MTKirk]

I have an '87 just like yours. My system has been flushed and has a new compressor, accumulator/dryer, & all o-rings. I'm using a hydrocarbon blend (enviro-safe) so the system functions almost exactly as the original r-12 fill. A couple of things.

First; moving the selector to defrost does not activate the AC on my truck (nor any other 87 I believe).

Second; My compressor will come on when I push the AC button even when it's below freezing, but; the cycle is very short (something like 8 seconds on, 8 off).

As mentioned up thread, your R-12 hoses will leak a little bit with r-134a in them. Also Ester or PAG oils used with r-134a will slowly dissolve your original o-rings and compressor seals, to be fully compatible you need to replace them with the correct HNBR material. Many people just refill their system every spring, eventually the leaks will become to large for this to be an acceptable strategy.

I believe you're just a little low on refrigerant (you can check this by sticking a jumper wire in the pressure switch harness, located on the accumulator/dryer), it's worth trying to top it off. If the leak is large enough that you are having to fill it up more than once a year it's probably worth it to fix your system (by replacing o-rings & compressor seals & maybe hoses). I strongly urge you to NOT USE ANY TYPE OF STOP LEAK. If you decide to flush the system later it makes it a royal pain.

The good news is that our trucks have AC systems that are incredibly easy to work on, you can remove every component (except the dryer which you'll replace) from the truck and flush them with a canister type sprayer in a couple of hours. The condenser and evaporator are easy to flush and are very rugged.

 

[Koch13351]

As mentioned up thread, your R-12 hoses will leak a little bit with r-134a in them. Also Ester or PAG oils used with r-134a will slowly dissolve your original o-rings and compressor seals, to be fully compatible you need to replace them the correct HBNR material. Many people just refill their system every spring, eventually the leaks will become to large for this to be an acceptable strategy.

Ok well that's good to know all of that. I'm assuming that since my low pressure line running across the back of the engine bay still has the (now crumbly) original insulation on it, that I still have R-12 lines. How do you tell them apart? I will look into that hydrocarbon blend you use, if you could tell me the brand etc.
sorry, not trying to hijack!

 

[MTKirk]

Ok well that's good to know all of that. I'm assuming that since my low pressure line running across the back of the engine bay still has the (now crumbly) original insulation on it, that I still have R-12 lines. How do you tell them apart? I will look into that hydrocarbon blend you use, if you could tell me the brand etc.
sorry, not trying to hijack!

From your description your hoses are for R-12. Some new hoses are marked as "barrier" or "134a" compatible but most are not. The old hoses last a very long time, they are protected from UV light & the inside is coated with mineral oil. I have several hoses in service that are over 30 years old, if you're going to use r-12 or a hydrocarbon I see no point in replacing them (til they have an obvious leak).

There are two larger brands of hydrocarbon refrigerant; Red-Tek and Enviro-safe. I use Enviro-safe because I can get it cheaper.

 

[Koch13351]

@MTKirk much appreciated! Thank you!

 

[HammerDown]

Well how about that...60 degrees today and the AC clutch engaged!
Good thing as It was pouring rain and needed to defog the windshield!
It is cycling though, so a recharge will be in order come Spring time

 

[F350camper]

sweet, good to hear.