Re: A/C problems, Help!

[Mitch Loescher <Loescher@tamu.edu>]

>When I start the car and turn on the A/C on LO, the compressor will kick in
>and the air temperature exiting the vents will begin to drop.  This only
>lasts a couple of minutes and then the compressor kicks out.  Then, no cold
>air for anywhere from 10 to 20 minutes, followed by the compressor finally
>kicking in.  The air gets cold (not real frosty - I suspect my charge is a
>bit low) and the cabin will cool down nicely after another 10 minutes.
>Sometimes the compressor doesn't kick in at first, but waits for  10 or 20
>min, and sometimes when the compressor does finally kick in it stays on
>(usually) while other times it is on and off intermittently.
>
>Here is what I have done...
>
>#1 - removed glovebox & inspected A/C programmer.  It appears to work fine,
>moving the cable throughout the full range of motion.  Gave cable a good
>shot of RemLube.

Rem Oil is good stuff, but the cable moves a flap that forces air from the
evaporator through vs. bypass the heater core...has nothing to do with the
compressor engagement.

>#5 - found the low pressure switch (under the plastic cover again) and
>thinking that my slightly low charge may have something to do with this, I
>jumpered the connectors to the switch .. still nothing

Good test. 

>#6 - took wire leading to compressor & connected to 12V - well whoop de
>freakin doo! the compressor kicked in!  Thus, it is not a problem with the
>compressor itself.

Another good test.

> - the gizmo behind the glovebox (the programmer, right?) only controls
>water and/or air flowing    through the heater core and has nothing to do
>with the compressor kicking in or out, right?

Oops.  The control head (I'm using Bentley terminology here) tells the
programmer to cut the compressor in or out, so actually yes, the programmer
trips the relay that engages the compressor.

Like this...

12V-----evap thermostat-----relay coil---programmer---ground.

12V----relay contacts----refrig low press sw----clutch----ground.

The realy is in slot 11 in the relay box unded the hood.

>- there is another relay under the dash that can be heard clicking on when
>the A/C is turned on (LO)
>does this relay control the compressor, or is it the one under the hood?

The one under the hood controls the compressor directly.  You can jumper the
big pins of the relay socket with the ign on to test the wiring for the
compressor clutch, and the low pressure switch.

>- are there any electronic systems that disable the A/C if there is a
>malfunction with the car? i.e. will the car disable the A/C if it thinks the
>car is overheating?

Yes, there is a switch (probably near the coolant outlet on the cyl head)
that will kill the a/c upon overheat.  ground=overheat, so unplugging should
activate comp if this switch is bad.

There is also (on most models) a full throttle kickdown switch that kills
the compressor on full throttle and then inserts a delay (12 sec) after you
release the throttle to prevent rapid cycling.  Have you been mashing the
throttle and broken this switch?  It's probably the one onder the gas pedal.

>- could the temp sensor inside the car be screwed up giving false readings
>to the climate control?

The LO setting is like a test setting causing the system to go on a/c full
blast, so this should override the inside air sensor.

>- is my low charge causing this whole mess?

Not if jumpering the low pressure switch still causes a problem.  The evap
isn't icing up is it?  That will cause the evap thermostat to shut off the
compresor too.  The relay jumper bit will test that.  The high pressure
switch can shut it off if the high side gets too high also.

 - Mitch Loescher