THSCC Forums

Got my 96 F350 running today after sitting for a couple of weeks with a dead battery. Everything seems OK, except the AC does not blow cold when the truck is idling. I took a look under the hood and the AC Compressor clutch was not engaged, so I revved the engine a bit and it engaged and the air blew cold inside the truck- for a while, then after several minutes of idling, the compressor clutch disengaged and the air stopped blowing cold again.

This truck does not have an electric fan on the radiator, just the mechanical belt-driven fan- and it's working fine (pulling air through the rad/condensor).

So, I'm thinking it's possibly a little low on freon (R134A)?? Or, maybe a bad pressure switch or some other problem.

Any other ideas from those who know more about this stuff than me? (which is pretty much anyone, since I don't know much)...


I don't have the hoses/gauges for the R134a so I can't check the pressures, but I do have a couple of cans of R134a so I could try to charge the system if it would take some.

http://www.harborfreight.com/a-c-manifo ... 92649.html

Worth every penny (after the 20% off coupon) IMO. You'll use them more than you might think. AC has both a high and low pressure cutoff, so just adding more blindly may not be a good idea. Obstructions in the valves also show pretty clearly on the gauges -- really high high's and low low's.

You can borrow mine if you want to do a test try.

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Mike Whitney
whit32@gmail.com, 919-454-5445
V10, V8, V8t, I6, I6, V6, F4t, I4, I4, I4, I4, I2, 1, 1

At the age of your truck it might have a sight glass. If so check for bubbling. All of my systems have only a low side cutoff or none at all. Of course 2 out of 3 of mine have carbs too.

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George Bright Member # 141
One of the youngest of the old farts.
Yes I voted against you joining the club.

Bret, check the voltage at idle. The clutch is electric and needa a minimum voltage to pull in. If the pressures were off, it wouldn't pull in even at fast idle since the pressure won't change until the clutch engages.
Charlie G

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1998 BMW Z3
1987 BMW 325is
2000 BMW
1996 F250 Turbo Diesel

hmm, good point- and easy enough to check. Alternator is fairly new, so hopefully it's doing it's thing, and one of the batteries is brand new.

George- I did a quick look and didn't see a sight glass, but I'll look again.

Mike- thanks for the tip, I'll look into that manifold set if it looks like the system needs some freon.

Thanks for the help guys - I'll post up if I find anything new.

I had a clutch on my 510 with AC that was voltage sensitive. It turns out that the gap between the ring and the pulley was too large. It had worn from many cycles. I managed to shim the ring back somehow and it would pull in at the lower voltage available at idle after that.

My site glasses are on the receiver dryer but a coat of grime will hide them.

_________________
George Bright Member # 141
One of the youngest of the old farts.
Yes I voted against you joining the club.