CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Ford AC advice, please

‘97 E-350, V-10 w/RV package, 260,000 miles. New (2,000 miles) Auto Zone clutch.

It makes cold air like crazy, in fact it frosts up the hoses in the engine compartment. I can’t turn it off. It’s stuck in the defrost setting. This is bad on cold nights.

Sometimes everything works correctly for a little while or till I go up a long hill so I made a new vac res but it worked the same.

I can remove a dash panel and watch the controllers move. When I have vac I can switch between settings and they all work. Then at the next change one controller closes and the other tries to move but fails. This is why I think I have a vac leak.

2 questions: Has my Auto Zone AC clutch failed so it always on?

Have you had this problem and found the vac leak? A new switch is only $50, if I remove the dash again I’m replacing it just because.

Thank you,
Ed

The “static state” of an unenergized AC compressor clutch is disengaged. A failed clutch would not fail “on”, it would fail “off” (refuse to engage).

Honestly, I can’t make heads or tails out of the rest of the question. I’ll defer to someone smarter than I.

“I can’t turn it off. It’s stuck in the defrost setting. This is bad on cold nights.”

The defrost position turns on the compressor. That’s normal. Sounds like a problem with the heater controls not working properly…

If you disconnect the clutch it should release. If the wire is disconnected but the clutch remains engaged it is jammed, seized, welded, whatever. But that is not likely. The relay that engages the clutch may be stuck in the closed position.

Those vacuum pods do fail with age so the one you see not working well probably has a ruptured diaphragm in it and yes, that would be a vacuum leak.

There may be several problems though. The icing of the accumulator could be due to incorrect system pressures, cycling switch not working correctly, and so on.
It could also be due to the clutch not disengaging fully. You did check the air gap on the clutch didn’t you?

The AC on all the time problem was caused by no clearance in the AC clutch. Two shims fixed that problem.

A bucket of water showed that my vac res had a small leak.

It all works now. This weekend when I drive to Willow I’ll find out if my vac res is large enough.

Thanks for the ideas.

The no clearance issue is the air gap that I referred to and should always be inspected when a clutch is swapped out on a compressor. Manufacturing differences can leave the gap too wide or as in this case, way too narrow.

I am curious how there was no clearance on the clutch.

Hi, I’m back…
No clutch clearance because I put it together without wrong. Fixed now.
My AC etc. is working well now except when the engine is under a big load like going up a hill. Then the AC, freash air or hot air comes out the defrost vents and not whatever I had it set on.

The check valve for the vacuum reservoir is bad or you still have a leak. Check valves are cheap, so I’d try that first. The default mode for the vent controls is the defroster. It will go there if it loses vacuum. When you’re pulling up a big hill, manifold vacuum will drop as the throttle is likely wide open, a normal condition. The vacuum reservoir is supposed to keep a reserve of vacuum to prevent the vent controls from losing vacuum. The check valve is supposed to keep vacuum in the reservoir when the manifold vacuum drops. But a bad check valve or a vacuum leak will cause your problem