My A/C isn't working, I've replaced almost everything.

[scott2093]

How would I go about testing the control unit? I have a multimeter to test the connections, just no idea what to look for on it

You can try downloading the electrical manual for the 1993 here. I don't see one for the 1994 but "should" be similar.

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

looks like page 153 on should give you the theory of operation and there are some tests later on. There is a schematic as well to help see what you're looking for.

Just be aware that, for some odd reason, there is some variation in the circuits among the years and the schematics may not reflect exactly what you have. But you should have enough info to troubleshoot. Post questions obviously if you get stuck.

here are a few screenshots ...

 

[docstoy]

Do you have a test light ? Ck for voltage at low pressure switch at accumulator or dryer, should have voltage with key on, a/c switch on with test light to ground and cking for voltage with connector disconnected,should be hot (light on) on one side, if you have voltage and pressure power then goes thru to high pressure switch at compressor then to compressor coil and then to ground . Your orifice is located at high pressure line at condenser you will have to remove grille to service it, hopefully it won't be stuck and can be replaced,make sure you reinstall it correctly and don't overnighter, you really need to evacuate system for at least 30 minutes to remove moisture (gage set and vacuum pump which were talked about before). This is if you have a 1994 c1500

 

[Noobular]

@Orpedcrow I wanted to also ask, the way to check the pressures would be to pull vacuum with the gauge set correct? cause obviously it wouldn't help to just use the gauge set on it seeing as I have to manually turn the clutch on by touching the connections on the low pressure switch connector?

 

[RacerM95]

Id be looking at the relevant wiring and the dash control unit

 

[docstoy]

You would be looking at pressures with ac gauges connected and screwd down to open valves on hoses, you would use gauges when evacuating (pulling vacuum on system) ,if pulling vacuum (vacuum pump) you should run pump for at least 30 minutes to remove moisture , and then close the valves on gauge set and turn off pump, allow to set for a few minutes , low pressure side should be -30psi (negative 30) this is showing you have removed refrigerant and system is holding vacuum, if you had compressor failure before replace orifice but by cking pressures first could show you if you had pressure on ac system which you have to have for compressor to engage, if you have pressures on high and low sides it could be electrical issue ( ck for voltage/ground)

 

[zevon]

@Noobular Humbled by my own experience delving into the AC rabbit hole and coming out the other side after years and several old cars and many dollars later to finally feel almost "comfortable" with AC repair, I can say that it cost me more to buy the tools/gauges/vac and AC parts, refrigerant and what-not-all else and also make several mistakes than it did to have AC professionally fixed and done with and a warranty

I'm a big-time 62 yr old DIY'r having managed many cars and trucks, with 1000+ parts ordered from RockAuto etc.. but i can still say unless your really going to invest the time (and money) and frustration to really learn to repair AC correctly then i'd avoid it until you are. Incorrect repairs will bite you back so DIY AC may not be the slam dunk, quick learn, cheap way out as (I too) expected!

Having said that, it is worth it to learn as I've since replaced the ENTIRE system (includes both evaporators) in my 99 OBS suburban. Dashboard comes down to get that very clogged evaporator out, etc. The under-dash evaporator in these trucks is NOT protected by a cabin air filter and are usually clogged like ****. Nearly impossible to clean well too because of it's location. Be sure to inspect it or all the other work will not result in free flowing COLD air.

I know this is not answering your immediate question but I hope it helps! Cheers.

 

[Schurkey]

The under-dash evaporator in these trucks is NOT protected by a cabin air filter and are usually clogged like ****. Nearly impossible to clean well too because of it's location. Be sure to inspect it or all the other work will not result in free flowing COLD air.

My '88, getting plugged with too many pine needles and cottonwood fluff.

You must be registered for see images attach

A vacuum, some compressed-air, tweezers and way too much time made it look much better. Still not perfect. Should probably be replaced.

 

[Orpedcrow]

Mine had screen door mesh attached to the output side… I did not put that on the new one. There was glue, staples and some kind of thread holding it in place.

You must be registered for see images attach

You must be registered for see images attach