Cars - '89 Corolla strange A/C problem (heat mixing with AC)

> wrote in message
ps.com...
> Hi,
> I have a mechanically excellent '89 Corolla whose AC has worked great
> until these past 2 years. I believe the heat's mixing with the AC and
> would appreciate your advice on how to fix it. The AC does function
> and I don't think the issue's low freon.
>
> Let's call the car's dash-level air vents #1 thru #4 to represents the
> driver's side vent, 2 center vents, and passenger side vent. When I
> turn on the AC, I get pretty cold air from #3 but slightly cold air
> from the other vents. When the heat is off (I slide the temp dial all
> the way to the left), I appear to be getting slightly heated air out of
> vents #1,#2,#4.
>
> I don't have a good understanding of where/how the heat and AC
> ventilation systems interface and why I'm getting colder air out of one
> vent than the other. How should I go about disassembling the
> ventilation system (do I do it from the firewall or via taking apart
> the dashboard? I assume #2) and what should I be looking for? I
> assume that I should also take out the radio and the ventilation
> controls and look around at how the ventilation controls are hooked up.
> My mechanic's never been keen on taking apart the car's dashboard so
> I'll need to do it myself.
>
> Thanks for your advice,
> John
>

There are 2 basic parts of the heating system - the temperature control, and
damper control.

The good news is that you can check the function of the heater control valve
fairly easily. In the engine compartment, somewhere on the firewall
(barrier between the engine and passenger compartments), usually somewhere
between the center and passenger side of the firewall, is the heater control
valve. It is located in the heater hose, which is a black rubber hose a
little thicker in diameter than a garden hose, coming from the engine and
passing through the firewall somewhere on the passenger side of the
firewall. The heater hose will have the valve in line and have a short
lever attached to a wire cable. If someone sits in the car and moves the
temp control from cold to hot, you should see the wire moving the lever
through its full range of motion. If you see nothing moving or it doesn't
move through its full range of motion, the wire may be broken or kinked
somewhere or the lever is binding. The wire passes through the firewall and
is attached to the temp control lever or knob.

Where the air is directed, i.e, dash, floor, or windshield, has no bearing
on temperature. If the air comes out of the appropriate vents when moving
the control, then it is OK.

You can check refrigerant levels fairly easily. Turn on the AC, move the
temp to cold, set the parking brake, and open the hood. In front of the
radiator will be a cylindrical canister called a receiver drier. The
receiver drier should have a small round glass window on top called a sight
glass. With the AC running, if you see foam in the glass, then the
refrigerant (called "freon" in the old days but not called refrigerant
134-A) is low and needs to be recharged. Based on the age of your car, that
is the most likely cause of the warm air.
--
Ray O
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