Spent some time today trouble shooting AC system. 2002 4.3L recently replaced lower intake manifold gaskets and valve cover gaskets, so I had a lot of stuff going on on top of the motor. found some dry rotted vacuum lines that I haven't replaced yet. One went to drivers side fender. Any ideas what that's for? Ok try to tell you what I found. I'll try to keep it simple by telling you what I did check. AC turned on nothing happens. Checked fuses, relay, switch on dryer (by jumping it out), and compressor (by connecting ground wire to coil under compressor relay). These all seemed to operate properly. Any help would be appreciated.

 

So does your blower motor not operate at all? Have you tried turning it on in a mode other than AC (heat, defrost, etc.)? How has that fared?

 

My guess is that your AC system is low on refrigerant "freon" 134a in a 2002. The switch that you jumped-out on the receiver dryer is a low pressure cut-out switch. When the system has a leak and drops below the minimum operating pressure, the cut-out switch opens the electrical circuit so that way the compressor can't become damaged by running while under-charged. The reason for that is because refrigerant / freon circulates through the system, along with the refrigerant oil. If it were to continue to operate while low on freon, then it would starve the compressor of proper lubrication and cause over heating and eventually compressor failure. 134a refrigerant is less forgiving than the older R-12 refrigerant that the older cars came with. So you're gonna wanna buy a charging manifold hose with a gauge that specifies when you've added the correct amount of refrigerant. It's pretty easy to under charge and ever over charge a system. In either case the system will not work properly.
I hope I've managed to give you a better idea of what you're facing, instead of making things more confusing lol. Good luck to ya.

 

Well picked up a set of gauges, been wanting a set for a while any way, My blower fan is working fine at all speeds. Clutch has no power even on defrost mode, the low pressure switch is in closed position (did continuity check). Took pressure readings , but this is new to me so a little confused on readings. Its still cold here this week 43 degrees this morning, so this may be adding to my confusion. I'm at a point now that I would like to try and find specific wiring diagram for ac system 2002 blazer, this would help me trouble shoot, and get me a little more familiar with wire harness under the hood. Tried to find some links here but didn't have any luck. If someone has this information it would be very helpful to me, my repair manual wiring schematic does not give much information, just shows wire going to PCM. Oh yeah, wrote down pressure readings from gauges, left paper at garage, so i'm going on memory, static pressure 74# high and low. Compressor running, jumped out, low 25# high 125#, ambient air temp 53 degrees. Lots of cold air coming out of vent. Temperature gauge in vent went below 40 degrees, then i stopped before I blew something out. If my memory is incorrect I'll put it in my next post. Hope this info helps you.

 

Here's the thing... when you jump out the low pressure switch, the pressures will continually increase. The Blazer has a cycling clutch compressor, you're supposed to take the pressure reading when the compressor clutch engages and when it disengages. If it was holding steady at those pressures, then those numbers are a bit low, and I'd be inclined to think that your refrigerant level is low, and that would be caused by a leak somewhere in your system - the schrader valves and condenser are likely culprits here.

 

Ok. Thanks for your help. I have left something out. To run ac compressor I have been jumping a ground to compressor relay which is located on drivers side wheel well. I'm doing this by placing a small gauge wire around coil ground side on relay and plugging relay in and then attaching that to ground. I may try to add image of this, i'm not sure if I explained that very good. If I just jump out low pressure cut out switch on dryer, compressor still will not come on.

 

Well, went in and took a better look. It appears that I did not connect wire connector to the back of ac compressor. This was causing compressor not to run. Is this a High pressure switch? Thank You guys for your help.