95 Saturn SW2 ac compressor

'95 Saturn SW2 with 156,000 miles. This cooling season the ac compressor won't engage causing only warm air to blow thru the car vents. System has a full charge - measured with recharge kit pressure gauge - no visible leaks, clutch is not frozen, fuses and visible wiring look good, system components seems to be in good order. Cooling system flushed/filled 2 years ago. Radiator fan operates normally when engine idles for a while and temp gauge rises. I've read in other forums about checking engine coolant temp sensors & expansion valves/orifices but not sure which direction to go in. Don't want to be taken by a repair shop...gut feeling is it's an electical/sensor issue I can do myself. Other than this, everything on vehicle functions as it should. Can anyone toss out some options?

Well I know that the ECTS you mentioned is an easy fix and is highly recommended to do even if you don't have any problems. 20 bucks from www.saturnparts.net. tool needed is 6 point deep well socket wrench and do not overtighten. May need a new connector for it also. I don't know if it will cause A/C/compressor issues though.

I've always thought that leaks may not necessarily be easily visible in the cooling system. A laser or dye or something may be necessary to be sure.

i'm not even sure if a bad ECT would disable the A/C on a S car. the cooling system is a seperate system from the A/C, they do affect each other, but not to the point the A/C wouldn't work at all. what is the gauge reading with the engine off? a fully charged system off will have about the PSI as the ambient temp in degrees F. when the system is running then it should be between 25-40 PSI. does the clutch engine? maybe take a test light to the compressor with the engine running.

i'm not even sure if a bad ECT would disable the A/C on a S car. the cooling system is a seperate system from the A/C, they do affect each other, but not to the point the A/C wouldn't work at all. what is the gauge reading with the engine off? a fully charged system off will have about the PSI as the ambient temp in degrees F. when the system is running then it should be between 25-40 PSI. does the clutch engine? maybe take a test light to the compressor with the engine running.
I think I've come to the same conclusion about the ECT sensor - the engine runs fine and dash temp gauge is functioning as it always has (correctly). Before I initiated this blog, I first checked the ac low pressure side with engine on - it was reading about 30-35 psi. Oddly, in response to your inquiry (days later and following a 250+ mile trip), I checked the pressure with [hot] engine off and came up with 20 psi...re-checked with engine on and came up with 20 psi again.

If compressor will not engage, can R-134 still be put into system without vacuum or is refrigerant can under sufficient pressure to force it in? I've read that low refrigerant will cause system to not function.

Should I try adding refrigerant with dye?

Any thoughts on refrigerant with sealer?

Also, not sure what you mean by "does the engine clutch". The compressor clutch will turn by hand - it's not binding. I'll try to take a volt/ohm meter to compressor and green lead going to it to test for voltage & continuity.
As noted in my intial entry, all systems/gauges/etc. of the car operate fine and within normal limits (EXCEPT the ac ... + defroster will not kick on compressor either). The AC and recirc lights at the dash switches light when depressed.

The refridgerant is under plenty of pressure to enter the system without the compressor turning. Some systems have a safety built in that will disable the compressor if there is a lack of refridgerant in the system to keep the compressor from destroying itself. Many times once some "freon" enters the system the compressor clutch will ativate the system.

sorry i ment to say "does the clutch engage", but it shouldn't with less then 35PSI static pressure.you obuviosly have a leak. if you don't want to take it to a shop you can try a one pound can. dye wouldn't be a bad idea,but most of the time GM adds it at the factory, so it may already be there, buy a blacklight first. DO NOT USE SEALANT, it rarely works, can damage you're A/C, and if it is ever serviced at a shop in the future, it will clog their several thousand dollar recovery machine and render it useless.

Still not resolved...here's the latest:

re-checked low side pressure with engine off and cold (85 degree outside temp) and came up with 25 psi (much hotter day than when I got the 20 psi reported previously...if that matters).
started engine & turned ac/recirc buttons on...pressure remained at 25 psi on low side...no movement at all.
compressor still not engaging.
tried to add additional R-134a using Interdynamics brand "Arctic Freeze +" refridgerant and trigger dispenser/gauge (www.id-usa.com (http://www.id-usa.com))...when I squeezed trigger, pressure gauge rose to 65 psi...when released, the pressure would slowly drop back to a solid 25 psi (took about a minute)...repeated this procedure with engine on and off about 6 times with same result each time. Almost seems that the R-134 isn't entering system but that refill hose is pressurizing and then de-pressurizing back into can. Nothing seems to be leaving the can ...doesn't get any lighter and no sound of contents exiting or can getting colder while transfer occurs. pressure held at 25 psi.
Checked low side fill valve by pushing it in to see if it was blocked or binding...it released a small amount of refrigerant and stopped as soon as I let off valve....seems OK (I've used the refill trigger/hose/ gauge on another vehicle and it worked fine).
Disconnected electrical connector on top of compressor and checked compressor for continuity...got a reading between it and ground so I think it's OK.
Checked for voltage at lead going to compressor connector...no voltage indicated between it and ground while engine running and ac + recirc buttons "on".
Tried setting dash control to "defrost" mode...didn't make any difference.
Lights at both ac and recirc dash buttons illuminate when depressed.
re-checked fuses...all OK.
radiator fan cycles on/off normally if vehicles sits and engine idles for a while (just as it should and has always done).
Re-checked all visible wiring...no signs of shorts, cuts, etc.
I think I agree that Engine Coolant Temp sensor is not involved as engine cooling system, idle, performance, etc. seems fine.As a newbie to this sort of forum, I don't know if anyone ever speaks live. If so, I can be reached at 914-262-3866 (cell) to talk about it.

if the system had a partial charge to begin with and you added a full pound the reading should have increased. possablitys-

you have a weird leak that is acting like a relief valve that won't let the system above 25 PSI

the charging can wasn't full

the charging can wasn't fully connected to the system

i'd check it over with a blacklight, and if you find nothing, add one more pound with dye in it and see what happens

To clarify for sierrap615...

I have not added any refrigerant into the low side valve...can't seem to get it in as noted in previous post...the connection of can/hose to filler seems OK...however, the charge pressure seems consistent at 25 psi
the refrigerant I tried to add has dye but I can't seem to get anything out of can...it was a brand new can and I can hear/feel the liquid inside it
I have a black light to use if only I can get dye into the system.

25psi on the low side without a/c running is low. After a few minutes of non-operation the high and low side pressures will equalize and should be in the 70+ range (I believe my Saturn and Windstars were close to 90).

I would only trust the cheap gauges that come on the re-fill cans as far as I could throw them. I picked up a "good" set of gauges at AutoZone for $50 that allows you to see low and high side pressures. Hopefully it gives accurate readings.

UPDATE: I found the problem! When trying to add refrigerant, I noticed that no gas seemed to enter the low pressure hose....I pushed down on the fill connector (hose coming from can) and found that the "plunger" inside it was apparently not depressing the Schrader valve down enough to open it to let gas in...when I pushed on the whole connector, that 16th - 32nd of an inch made all the difference. Was able to fill system and get cold air blowing...UNFORTUNATLEY, the refrigerant has been leaking out slowly as the Schrader valve won't seat itself. I have to replace that, refill system with refrigerant, and hopefully the issue will be closed. The Schrader valve sits too deep for the valve removal tool I use on my bicycle so I need to look for one with a deeper reach. Any closing comments from anyone on tricks to complete this task?

technicly, whenever the system is opened it should be pulled into a vacuum to remove all air from the system, and the receiver/dryer replaced, but if the system is holding some pressure now, and you change the valve very quickly(no more then a few seconds) you might get away without taking it to a shop. wear gloves to prevent frostbite.