I've been noticing lately that my a/c isn't what it used to be and was hoping to get some suggestions on what could be going wrong. Truck has about almost 90k miles. For the last year or so its been doing a lot of sitting but then within the last few months I've been on some long trips towing a trailer, often in 100+ degree temps.

On these trips the a/c sometimes isn't quite cold enough to keep the cab at a comfortable temp. I find my self putting it on Max AC setting more and more, which I've never had to do before. A lot of times it seem to be related to the outside temps and as I'm driving and notice the ac warming a bit, I will look up and see that its 100+ outside. Then other times it can be really hot outside and the ac is working fine, or vice versa. I noticed that it seems to happen when the engine is under heavy load as well..

My local dealer had a $49 ac diagnosis so I took it to them and they said I needed a new compressor and total bill would be almost $1100. Well, I just don't trust them and told them no thanks. I'm picking it up this afternoon when the wife gets home.

Any help diagnosing this problem would be greatly appreciated.

 

Compressor clutch may be worn..... look at it while on (and the inside of vehicle is HOT)and see if it stays engaged. If it doesn't, all you may need to do is remove a spacer on the shaft behind the clutch.

Look at this post: https://www.ford-trucks.com/forums/8...tch-shims.html

 

Also possible the airflow though the condenser is diminished.

You'll really need a set of gauges to troubleshoot it.

 

I did this when I got the truck home and then realized you said with the cab hot which it wasn't. It never disengaged but I'll try again tomorrow to see what happens.

 

Here's what the dealer's notes said, if it helps any:

 

Too bad they didn't give pressures...

If they only pulled out .65 kg of refrigerant, the system was undercharged (capacity is .94 kg). Undercharged systems often manifest as a noisy compressor. For whatever reason, you have a leak which would explain your initial symptoms. I'd be skeptical of their "diagnosis". Now you know why it was only $49.

I'd have the system charged with the correct amount of refrigerant including UV dye and see what develops.

 

Assuming there is a leak, doesn't that need to be found and fixed first before they will charge it to the correct amount?

 

Yes, that's the way they are "supposed" to do it. Your system should have had UV dye in it from the factory for just that purpose.
Pre R134a, dye wasn't added to systems during assembly, so you would need to charge the system to leak test it (dye or sniffer). Since 1993 and the change to R134a, most (all?) systems have UV dye installed at the factory. I believe this was mandated by the EPA, but I can't say for sure.

It's possible that your compressor is weak, but I doubt it. Like projectSHO89, it sounds like the system was undercharged due to a leak. Noise, low pressures and only .65kg of refrigerant seems to bear that out.
Keep in mind, though, that the compressor "could" be damaged and causing the leak. It's a chicken/egg situation that can only be determined by seeing the vehicle in person.
I would get another opinion.

 

For the "cheap" fix, I'd pick up a charge kit at auto parts store WITH gauge and charge the system..... also pick up new caps for the schrader valves. If the small leak isn't coming from the valves watch for the dye traces.