1998 Blazer LT 4WD

AC doesn't cool is the basic problem, however

If I jumper the clutch on the compressor the AC cools well so something is keeping the clutch from engaging.

I've :
Checked all fuses and relays
Replaced the switch on the receiver/drier
Replaced the receiver/drier
Evacuated the system, drawn a vacuum, added freon

Remember it cools just fine if I apply 12v to the ac clutch.

ideas - suggestions? What would keep the ac clutch from getting the right voltages to make it engage?

Also when the ac button is pushed inside the light flashes for several seconds and then goes off.

I've got the compressor that sits on top of the engine. I see no other sensors on the compressor or ac lines.

 

Manual or auto AC?

George

 

The switch on the accumulator can fail but you have replace it. That switch is in a series circuit if I recall. I don't know if there is another switch that has to be closed between it and the control circuit in the passenger compartment.

And yes, as George asked, is it a manually controlled system or a "Computer Climate Control" system (i.e. you set the control to a temperature that it tries to maintain).

 

I have a similar issue on my 1995 - Just bought it last weekend and the clutch is not cycling.

Could you tell me what pins you jumpered and what switch/unit you jumpered?

 

Again, manual or auto AC, the wiring is different.

George

 

My bad - manual AC and again sorry for the thread hijack...

 

On a 95 with manual Ac:

light green wire wire leaves dash module to low pressure switch on the accumulator (closed for cooling) energized with 12v with call for cooling.

Dark green from accumulator to compressor clutch relay power feed on cowl. Control for relay coil is fused power and the ground is switched by the VCM.

White from relay output to high pressure switch on back of compressor (closed for cooling)

dark green from HP switch to cable splice then dark blue to compressor clutch. Clutch ground is black through a splice to G114 on the block.

you can test for 12v or hot wire 12v (fused) from either end working your way to the other end. The quickest and safest is test with a meter and start at the clutch end to see if you have a call for compressor (12v). If not, check the other end at the accumulator.

note to the OP and others searching this thread that the wiring changes significantly on different years and on auto Ac. Newer auto models do not use this simple series power approach.

George

 

Many thanks and repeated apologies to the OP... See comments in you text.

I jumpered 12V directly to the Compressor clutch and it engaged. I hooked up an recent bottle of refrigerant that felt still very full. There was no pressure on the low side and the refrigerant would not flow in.

I also switched the cowl relay for it's sister next door so without bench checking the relay I am pretty sure it is good. Fuse also good.

It seems that the low pressure switch on the accumulator is failed - I could not reach around and check for continuity but also am unclear what activates the switch - is it 12V signal or the presence of "some" pressure in the system - i.e. having at least a basic refrigerant charge?

Anyhoo - Is the next step a new accumulator switch and/or accumulator? Or to get a new bottle of refrigerant and see if I can make it take a charge.

 

You either have:

A failed low pressure switch at the accumulator
Insufficient pressure at that switch to close it (usually > 30-50 psi)
A wiring or connector problem

What is the low pressure reading at the low pressure port with the engine off?

What happens if you pull the connector at the low pressure switch and jumper it with a paper clip for just a couple of seconds? Does the compressor clutch engage?

George

 

A nice thing about a bad pressure switch on the Accumulator is that it can be replaced without having to vent the AC system. These parts are not crazy expensive either.