1991 S10 Issues

[philipk1965]

Hi Everyone,

I have a 1991 s10 with a 4.3 L The past few month the AC isn't as cold as it used to be, Naturally thought the refrigerant is low. So I charged it with one can. 14 oz.

It took awhile for the can to empty and the compressor cycles on and off every 3 seconds. the AC is little bit colder now. Here's the numbers off the gauges.

Static - L 53 H 75

Running - L 65 H 50, then down to 25 with compressor on, then back to 50 and over and over like that.

Running with pressure switch bypassed - L 72 H 0

Running with compressor unplugged - L 66 H 65

[Cusser]

1991 S-10 was R-12 from factory.

Was this ever converted to R134a?
Did you add R-12, R134a, or "miracle in a can" ?
Post low and high pressures at 1800 rpm with engine and compressor engaged.

[JohnHere]

These questions and suggestions ^^

I believe your S10 came from the factory with an R4 compressor, which isn't known for its trouble-free performance. To your knowledge, was the compressor ever replaced?

Based on your posted running pressures, I'd guess that the compressor is shot.

Also suggest not electrically jumping anything.

How many miles on the clock?

[philipk1965]

Cusser It's still an R12 system and I put in R12.
L 65 H 50, then down to 25 with compressor on, then back to 50

JohnHere Yes the compressor was replaced many years ago. The truck has 350K on the clock.

[JohnHere]

In view of the vehicle's mileage and age of the compressor, I'd say that the R4 is due for replacement.

If the S10 is in good overall condition and you plan to hold onto it, I suggest fixing the A/C now that we're approaching the Summer season.

Do you have enough R-12 to charge it when you're finished with the repairs? If not, and you don't want to buy more (R-12 is expensive and hard to find nowadays, as you might know), this system probably is a good candidate for converting to R-134a.

Whether kept R-12 or converted, the list of parts to purchase for this project are a new (not rebuilt) compressor, new condenser, new accumulator, new orifice tube, new pressure switch(es), plus all-new seals and o-rings. The evaporator, which is usually hard to get out, can be back-flushed in place. The tubing and hoses can also be removed and flushed as long as they don't have in-line mufflers (can-like devices). Otherwise, they'll have to be replaced as well. The idea is that you don't want any traces of the old oil and/or debris to remain in the system.

If you're located in the USA, Tim at ACKits.com, this Forum's sponsor, can help with the parts, tools, and materials you'll need.

[philipk1965]

UPDATE!!!! The gauges on my manifold were backwards!

I did the pressure readings again.

L 37 H 85, then falls to 65 then compressor starts bring it back to 85.

Any ideas from the new readings?

Thanks!

[JohnHere]

You didn't mention whether you're doing this, but the correct way to test an A/C system in the shop or at home is to note the ambient temperature in front of the grille (not the weather-report temp), set the engine at about 1,800 RPM, A/C on Max, blower on Medium, and doors/windows open. By doing this, you'll maximize the heat load on the system to see how it performs "under stress" by checking the center vent temperature, pressures, compressor noise, leakage, etc. The ambient temperature directly affects the pressures, particularly on the high side.

Regardless, the system pressures on your S10 are still very poor, pointing toward a worn-out compressor, which probably has disintegrated internally, spreading debris downstream. You'll still need to overhaul the entire system as detailed earlier.

When you disassemble the system, pay particular attention to the condition of the Orifice Tube. If the OT screen is full of black gunk, metallic particles, and plastic debris, the compressor is done for.

Just wondering, is your S10 a Blazer or a Pickup Truck?

[philipk1965]

pick up

[philipk1965]

I checked the continuity of the pressure switch. It read 0.

Which is good, right?

The pressure switch either is working or not. Is there such a thing as a weak of half working pressure switch?

[JohnHere]

I checked the continuity of the pressure switch. It read 0.
Which is good, right?
The pressure switch either is working or not. Is there such a thing as a weak of half working pressure switch?

If the low-side running PSI is approximately in the mid-20s to mid-30s, then the pressure switch on the accumulator should be "closed," or infinite ohms on a multimeter, which would cause the compressor to engage. If a correctly functioning pressure switch senses abnormally low or high pressure, it would "open," disengaging the compressor. So the zero ohms reading that you tested means the switch is "open."

Normally, the pressure switch is either working or not, but they usually fail "open," or compressor disengaged.