A/C problem, compressor engages & blend door OK

[keith1764]

As the title says, I'm not getting cold air from the A/C, but the compressor engages and I've checked the blend door and the actuator. I don't have gauges, but since the compressor is engaging I'm guessing the pressure is fine at least on the low pressure side.

[gmtech1]

Originally Posted by keith1764

As the title says, I'm not getting cold air from the A/C, but the compressor engages and I've checked the blend door and the actuator. I don't have gauges, but since the compressor is engaging I'm guessing the pressure is fine at least on the low pressure side.

REALLY need the pressure readings on this. Just because the compressor is running doesn't mean it's building any pressure.

[keith1764]

Originally Posted by gmtech1

REALLY need the pressure readings on this. Just because the compressor is running doesn't mean it's building any pressure.

Still no high pressure side info, but I borrowed the neighbor's fill hose w/ gauge and it pegged past 80 psi.

I recently evacuated the system to replace the high pressure port and the stem in the low pressure port because they were both bubbling. I only put two 12 ounce cans and part of a third (I used the same gauge and put in the proper amount for the ambient temp.) when I finished, so the high reading on the low pressure side isn't from overfilling.

Before I replaced the port and the stem and evacuated the system, the gauge pegged in the negative direction when I checked it.

[Tech II]

Is that one of those guages on a can? Very unreliable....

If the compressor is running, and you are getting an ACCURATE reading, from the low side, what is the reading when the compressor shuts off? If it is the same, then the compressor is shot.......if it goes much higher, the system is overfilled....

[keith1764]

Any chance it could just be a clogged accumulator or orifice tube?

[Tech II]

If the system was clogged, that compressor would not run...it would shut off on the high pressure switch......

You must put a "good" set of gages on the low and high side......readings of both sides should be equal, with the compressor off....on a cold engine, pressure should be approximately the same as ambient temp.....so if it is 70F outside, the pressure on the lo/hi sides on a cold car should be close to 70 psi....if much higher than that, it is overcharged.......now start the vehicle....turn on the A/C....the low side should drop to around 30 psi, and the high side should rise to at least 140 psi....the pressures will vary slightly due to ambient temp, load, and humidity....

If the low side reads 30psi, the line should sweat and be cold to the touch....if it reads 80psi, it will be warm to the touch......

[keith1764]

Originally Posted by Tech II

If the system was clogged, that compressor would not run...it would shut off on the high pressure switch......

I'm pretty sure there is no high pressure switch on the 1999 s10. Only the low pressure switch.

Funds are tight, but I'll try to get a gauge set next week. I saw a Mastercool set I think I can afford.

[old_master]

There are 2 switches: The clutch cycling switch is on the accumulator. It should cycle the clutch so low side pressure cycles between 22psi and 42psi. The high pressure cut out switch is on the rear of the compressor. It will not allow the clutch to engage if high side pressure is above ~380psi. TechII is right, you really need a manifold gauge set, a good quality evacuator, (or an old working, refrigerator compressor) to diagnose and charge it correctly. If you understand how and why AC works, it will be your friend. If not, it can cause serious damage to the system and YOU. When you have the proper tools, let us know and we can help you.

[keith1764]

Well, when I got the gauges the system was low on refrigerant due to the stem I replaced and I know I finger tightened as tight as I could with the tool that was provided was loose. I don't know if it was vibration or what.

Now the system is working again. I think there's some debris that keeps stopping the system up. The last time the A/C quit working I had a vacuum on the low pressure side. After emptying the system to install the previously mentioned stem and high pressure port (they were bubbling) it worked until I had the problem I described in the original post.

As for the high pressure on the low pressure side, I had my mind on some other things and I'm pretty sure I forgot to crank the car before checking the pressure.

I guess I'll wait and see what happens this time. Thanks for the help. I'm sure I'll be back with this problem. At least this time I have the gauges to help figure it out.

[Blue Bowtie]

Debris should get caught in the strainer at the orifice tube. If the problem persists, the system may need to be reclaimed and the tube replaced. They're usually less than ten bucks.