Ive been looking into my AC not working. My first thought was maybe low on refrigerant, so i hooked up one of those do it urself cans at the store, well nothing happend, no clutch engaging on the compresser. I though maybe a fuse or relay, nope both good. I know i cant charge the system until that clutch works. I got the multimeter and checked for voltage to the clutch, nothing. I lose track of the current after it leaves the fuse, but i do have power on both terminals of the fuse so i know its good. Next thought was a pressure switch, so i used a paperclip to jump the switch by the compressor, nothing. I moved to the one on the reciever/dryer thing, and away we go. So now I can make the compressor turn but still have no cold air and i am not leaving the paperclip in the plug, actually its already back where it belongs, i dont like riging things up, i want it to be right. So my question is, do i have to trick the system like a caddy to charge the AC or do i just have a bad switch, I have not yet found any info on the resistance or anything on the switch that i can use to test it. Any help would be great, AC time is here

 

hmmm I can't help you, but I am watching this thread because I have the same problems, and I also would like to get it working soon... mine hasn't worked since I got the truck

 

I would recommend you check for continuity in all the wires and loads. I dont really know anything about the AC systems, but I can sort of help with the electrical part.

 

first off if it needs refrigerant than it has a leak, you can use a paper clip to keep the compresser ingaged to help to put refrigerant in only. you really need gauges to see if you have anthing in the lines or not. to do it right u need to put the systems under vacuum first for a leak down test and the other to get the correct amount of refrigerant in the lines.

 

here is my two cents since i have been going through this ac ordeal since last year. in order for the compressor to engage there needs to be refrigerant (obviously) but then there is a switch on the compressor. i believe if there is not enough pressure in the system it won't cycle on. from what a local shop here told me was that you can't replace the switch on it. must replace the compressor. the low pressure switch on the dryer can be replaced.

maybe this is off your topic, but i cant see why the switch would not engage unless not enough pressure or it is shot.

 

I know that obviously u need refregerant for it to operate. I know that the wiring to the compressor is good because it came on when i bypassed the lowpressure sensor. I know that the high and low pressure sensors control the cycling of the compressor clutch. The switch on the compressor is the clutch. Sometimes u can get just the clutch, sometimes it comes only with the compressor. If ur pressure drops below the set pressure of the low side sensor, it will kill the compressor, same if it rises above the high side. I have charged systems before on other vehicles that were completley empty just by hooking up a can to the low pressure side so its odd to me that the truck doesnt charge. My old blazer took 4 cans and a can of stop leak just to puck it all back out the next day, but as soon as i hooked up the can, the compressor kicked in and it was dry for three years. A can of good stopleak will fix most minor problems, but not always, i want to try this first because it contains the leakfinder dye. The PO said that he didnt charge the AC when he put in the newer engine but it worked fine before he pulled the old one, so im hoping for some good luck. My co-worker is bringing in his guages and we r going to try to get it working tomorrow, I will post my results tomorrow night.

 

if the system has been opened to out-side air u must put it under vacuum first. if not it will not get as cold as it should !!!!

 

If the previous owner just bolted up the old AC unit and didn't charge it, I'm sure he didn't change the drier or pull a vacuum on the system so I doubt just adding freon is going to do anything.
I'm currious if he used the compressor from the old engine that worked or from the "new" engine.
If you've got power to the compressor and you jumpered it and it doesn't kick on, I'm wondering if the compressor isn't siezed up? The only way I know to check it is to take the compressor apart.
Regardless, once you get the compressor issue sorted out I'd do the following given the system has been opened:
Disconnected all the a/c lines everywhere there is a connection and flush each line section with some A/C Flush (usually on the shelf next to the "freon". Then blow lots of compressed air through the lines to get rid of the flush.
Replace all the orings you find.
Replace the drier.
Add compressor oil to the compressor.
Bolt everything back together and pull a vacuum on the system. You need a strong vacuum pump for this. If you don't have one, take it to a shop and have them pull a vacuum and test it to make sure it holds the vacuum. They would probablly add the freon for not much more than it would cost you to do it.
Chime in if I'm off base here.

 

he is telling u right

 

a/c's sometimes need a refill on "oil" as well as freon...