OT: '95 chevy problem

Bear with me, this is gonna be kinda long. :>)

Number one troublemaker with those systems is the orifice tube in the high-pressure line out at the condenser. It has a small screen on the upstream side and if it is plugged it shuts the whole show down (read: system plugged).

Secondly, check both of those pressure switches. They have to work correctly in both modes so that the computer knows exactly what to do with that compressor; I.E. Turn it on or KEEP IT OFF.

Check all fuses and relays to make sure they are functional.

Look at the air gap on that clutch. Does it seem excessive (see picture)? That thing cycles a lot and they can get wobbled out to the point where they won't engage.

Now (and this is the headache), if you reset the control head, the system is charged with gas, there is no blockage, both low pressure/high pressure switches are good, air gap is correct at the compressor clutch, condenser cooling fans are okay, A/C relays functional and the silly thing still won't come on, you need a control head.

It happens.

Wiring is fairly straightforward and simple. Power at the compressor at all times via the fuse block. Ground side is controlled by that control head and the circuit will only be engaged if all parameters are met.

Sure hope this helps as I'm pulling it up from the deep recesses of my old memory. The only place that schematic is available is in the $150 shop service manual from GM, as far as I know.

Hope ya get 'er, as they can drive ya crazy sometimes.

Allan

I'm gonna go out on a limb here even tho I'm admittedly really, really old and quite feeble minded. Also, bear in mind that I haven't worked on one of these things since back in the late nineties.

However, you already know that there is 12 volts at the compressor and also that the clutch works because you've sucked 'er in manually by the use of jumper wires. Therefore, you've just about covered every area of that system electrically from the grille emblem back to the rearview mirror.

Down, fast and dirty diagnosis: Only two things that will cause that compressor to not engage now is a block by the pressure switches or a bad "dash" head.

You say it is NOT low on freon.

I may be wrong; been wrong a million times before, but I think you've got a quad-driver fault (output transistor) in that control head at the dash.

Allan

As I posted before, IIRC, there's a power relay located BETWEEN the control head and the AC clutch that does the actual power switching, as commanded by the control "head".

I'm ALMOST certain it switches POWER to the clutch (NOT the ground, as another poster thought). I'll remain "open-minded" on that, though, and please correct me if this turns out to be wrong!

The clutch ground wire PROBABLY grounds to a stud in the aluminum intake manifold, and there HAVE been problems with those grounds getting dirty and corroded.

Before I "threw money at it", I'd probe BOTH wires at the clutch connector. I'm almost certain the BLACK wire is GROUND, and the GREEN wire is power... "HOT" when the clutch is supposed to engage.

A poor connection in either the ground or the power circuit could certainly be causing the problem, as well as a bad relay OR the control head, or pressure switch... I'm NOT sure if the pressure switch actually carries the clutch current in this model, or if it "signals" the control head.

If you REALY want to know what's going on, for $24.95 you can get one-year access to service information and wiring diagrams from ALLDATA.

• ALLDATA

I'd have to look at that particular schematic for all the circuits and sub-circuits, but GM's processors always worked on the ground legs, never the "hot" side, weather it be to control mechanical relays, solenoids, step motors, etc.(of that era anyways).

And, like I say, I'm totally going from memory and we all know what a problem that can be. :>)

How goes the battle up there? Are ya keeping ahead of the race?

Allan

That compressor is controlled by a "computerized" control head.

Most likely reason is that the system is/was low on freon and repeated tries at cycling will trip that dude off completely until you fix it so as to save the compressor from burning itself up.

If you are absolutely sure the system has gas, unhook the battery for 10 seconds and it will reset that control head.

Allan

Maybe something similar is happening with yours, or maybe not.