1990 chevy ac problem
 

I've got a problem with my clutch engaging on my brand new ac compressor in My 1990 Chevy Silverado 2500 Rwd 5.7 liter . The guy I bought it from said it had a bad compressor . It was drained of all refrigerant due to a hole in the line.( Ac compressor to condenser and accumulator)
I replaced the compressor, the line, and added freon. The clutch wasn't engaging so I replaced the AC pressure switch (Plugs into accumulator) . When I did I noticed the valve the switch Threads on to was slowly leaking air . I don't know if that's normal. After that I ran a wire to both prongs on the AC pressure switch pigtail the clutch came right on. I replaced the the switch and the pig tail and now I'm not sure what to do now. Any help would be appreciated thank you

If you vacuumed the air out of the system, did it hold vacuum?

its not normal but the switch should seal it up. its pretty much a schrader valve that would be in a valve stem.

ok let me try to understand, you jumped the pigtail and the clutch came on. then you replaced the pigtail and low pressure switch (on the accumulator) and the compressor wont come on? is it possible it still doesnt have enough freon?

I did not use a vacuum at all And I'm getting a full reading on my gauge but the freon isn't making its way through the entire system because the clutch isn't activated. Maybe if I hotwire my pigtail and then add freon .can't try that until later though

Just re-read your original post. If the system was left open for so e time you should replace the accumulator also along with the orifice valve. Then vacuum they system, the accumulator has those little white things in it to remove moisture, the same thing you find I. Food and shoes.

If the system is open too long they won't do their job and you have moisture in the system and it will be like acid to the system. The orifice tube acts like a check valve and filter, if the compressor went out it's probably filled with metal. Putting the system under vacuum will cause the moisture to evaporate and will allow the accumulator to do its job. Just throwing it back together will cause all sorts of issues and you'll notice the freon being sucked unto the system if it's under vacuum also

Thanks for the feedback. This seems like a logical explanation. I'll pickup the accumulator and orphix this weekend along with a vacuum pump. Hopefully that solves the issue. California Summers are no fun without ac. I'll keep you posted

Not vacuuming down the system will cause lots of problems, besides the air displacing the R-134A. Vacuuming it down boils any condensation out, else you can have corrosion form in the system. It also helps check for leaks as the vacuum will up to atmo pressure if there is a leak.You can do a good job of this or a bad one. Its up to you.