Air-con gurus...help please!

[southernspeed]

My air-con has worked great for the 11 years I've owned the truck. I've had it re-charged about 8 years ago.
Last week it started playing up. It'll work as normal for ten minutes and then stop working, just putting out ambient air.
I paid £85 ($150) to have it re-charged today with new valves and a catalist to run on 143 ref.. and it's still the same! After 10 mins it stops drawing the clutch in on the compressor.
Anyone point me in the right direction?

 

[goldwing2000]

I'd say either a clutch cycling switch or the clutch itself.
First and foremost, check the ground to the clutch. You should have constant ground.

After the system stops working, do the floowing:

Check the power lead to the clutch. If you're getting a 12v signal, then the switch is ok and the clutch is probably bad. It's just a big electromagnetic coil and they can develop heat-related shorts and opens. To verify, check the resistance between the two wires of the clutch coil. I don't recall the spec off hand but if it shows infinite resistance, it's open. If it shows less than about .5 ohm, then it's probably shorted.

If you're not getting a 12v signal, then the cycling switch is probably bad.

Next, check for 12v at the cycling switch. If you don't have 12v there, then the problem is somewhere in the control circuit.

If you have 12v to one side of the switch, jump the two wires together and see if the clutch pulls in. If it does, then the switch is bad.

If it doesn't, then jump a 12v wire to the signal wire of the clutch. If it pulls in, then you have an intermittant open between the switch and coil. If it still doesn't pull in, you'll have to replace the clutch coil.

 

[southernspeed]

OK thanks. Sorry to sound like a dork but I know nothing about a/c, but which is the 'cycling switch'?

 

[HarryH3]

There's lots of great info available about auto a/c systems at:

www.autoacforum.com and
www.ackits.com

 

[southernspeed]

Thanks. That gives me a few things to try!

 

[goldwing2000]

OK thanks. Sorry to sound like a dork but I know nothing about a/c, but which is the 'cycling switch'?

It's a little doo-dad that's threaded into the a/c line and has two wires going to it. Look around and you should find it pretty quickly.

 

[cbbr]

Mine went bad, actually was cracked, and had ethe same type of problem. Good news is that its cheap and easy to fix.

 

[sandawgk5]

The easy way to tell if it is the cycling switch is to short the two wires on the conector. That will cause the clutch on the compressor to engage as long as the wires are shorted. I used this method to determine if my problem was a switch/pressure issue or if my clutch was bad. My switch was located on my dryer canister.

Ira

 

[southernspeed]

Found the problem thanks guys. When I had the compressor off to change my engine I left too much air gap on the clutch.
Unfortunately I just tried to pull it in closer with the centre nut and stripped the thread ....what a dohnut!

 

[HarryH3]

Usually the center nut will strip, but leave the threads on the shaft intact. You have to use the correct tool to get the gap to close, it engages ALL the threads on the shaft. Once you have the gap set correctly, then install a new retaining nut.

 

[southernspeed]

Thanks. I managed to 'manipulate ' it and have a good airgap now!
Now I just hope this 'conversion' the guy did is ok and won't give me the 'black death' I've been reading about!!