A/C Problem on a 1996 850 GLT

[waterheart776]

Update:



Went out to repeat charging procedure on car. This time, I made all the connections with the engine off (daylight is a big help). Started up the engine, turned A/C to max cool, no recirc. Compressor and fan engaged simultaneously. Pressure on meter dropped to 35psi from 100. Temp outside was 90 degrees. Air inside still blowing hot. Attempt to charge. There's refrigerant flow, but no cold air. I have my friend rev the engine up to 2000 RPM, meter drops to 23/24psi. Compressor still engaged. I depress the trigger, and can feel refrigerant moving. The bottle gets incredibly cold. All of a sudden, compressor cuts off with cooling fan still engaged, and meter goes back up to 100psi. My friend reports that the air got cold for a minute, then got hot again. I turn the A/C switch from auto to off to repeat the process. Wait 10 seconds. Turn it on, and A/C compressor engages. Meter drops back to 36-37PSI. Friend revs up engine, it drops to around 24/25psi. I try to charge some, and compressor cuts off after rapidly cycling 4 or 5 times before that. I time my bursts for when the compressor is ON. After that, meter goes back up to 100psi. The next few times switching the A/C switch on and off, it does nothing other than engage the cooling fan, but not the compressor. I'm guessing that:

A: There's a charge in the system, and it's good.

B: Something's obstructed somewhere, preventing proper refrigerant flow. The air getting cold all of a sudden then hot might indicate this.

C: or, there's something else wrong. (Possibly a leak? The meter indicated a steady 35psi when the compressor was engaged and the engine was idling) The receiver/dryer (accumulator), or the Evaporator coils? Anyone have any ideas as to what might be going on here.


--John


EDIT: The Schrader valve on the suction port is good, and the fitting was depressing it properly.

Also, at a couple of points the compressor went from cycling to steady on, and stayed the way until the engine revved up, then cut off, and did not cut back on until I reset the switch, and gave whatever relay or electronics that are in the pathway of that switch enough time to 'reset'.

[Ozark Lee]

Your pressure readings sound good (Still a fuzz low on the higher RPMs). Was the engine hot while you were doing this?

You may have the damper door(s) stuck in the full heat position and the A/C just can't overcome the heater. Is the temp the same on both the driver's and passenger's side louvers?

...Lee

[waterheart776]

Lee,


Yes, the engine was hot when I was doing this. She had just parked the car and handed me the keys.


I can believe the damper problem being the culprit. Is it pneumatic on this vehicle, or electric? Because if it's the former, that means finding vacuum lines.

She's taking it into repair, with this thread printed out to hand to the mechanic. Maybe it'll save them some time (and her some money) if I go with her, and they see this. After all, they'd have to do the same kind of troubleshooting steps I did.


Thanks,

John

[Ozark Lee]

The damper doors are driven by electric motors if you have the ECC (Mechanical cables if it is the MCC) but I have had damper doors stick on both varieties. A big problem with them is that the spline at the end of the damper shaft will split with the ECC. There are some remedies that range from chopping of a .44 magnum shell casing in half to wrapping it like a fishing pole joint to fix the broken joint if that is your problem. There are several writeups in the repair database.

These are things that a mere mortal shadetree mechanic can fix - it may not be pretty but it will work.

...Lee