I have done a search on here and read many threads on this, but none were totally on subject or took the discussion to a complete explination. I have a 91 L98 coupe. The compressor ran fine before I started. I had some wear and tear on an a/c hose which looked like it was about to burts, so I replaced it.

I am trying to get my Compressor to run for charging. I had flushed the system, replaced the oriface and accumulator and drew a vacuum, which it held for several hours. I attached a can of refrigerant to my charging hose and injected it into the a/c system using the vacuum and pressure in the refrigerant can to move the gas. I expected to start the engine and use the compressor to complete the charge, as normal. So far, I have been unable to get the clutch to engage and run the compressor to do that. I've checked all fuses. I know there are 3 switches on the a/c lines. one is over pressure protection, one is clutch cycleing switch, and I forget what the third one is for. Which is which? I have read that you can/should short across one of them (I assume the clutch cyceling switch) but I'm not sure which one that is. There is one by itself up on the evaporator inlet, and two down on the hi-side line by the fender skirt.

Any help on this or other aspectes that may get the compressor to run woould be appreciated.

 

Was it working before you did the work? Did you bypass the low pressure switch ? It's located at the dryer/ accumulator. disconnect it and bypass. Are you're fans kicking on? You can also check you"re fuse links behind the battery.

 

It should charge just by the pressure in the can. You don't have enough pressure in the system to close the low pressure switch.

If you're using the kind of charging hose that pierces the end of the can with a needle tip, open the valve -all- the way.

 

I don't have anything at the dryer/accumulator. As I said above, I can only find 3 switches. One, up at the inlet to the evaporator, and two, side-by-side, down on the hi-side aluminum tube near the rear fender skirt. The accumulator is up front by the radiator and has nothing electrical near it.

Yes, it was working prior to repairs.

 

I feel your pain- I just redid my 90 L98, using R-12. rebuilt compressor- what a piece of cake! replaced all the o-rings, pulled a vacuum for 6 days! I too used the vacuum to suck in a can of r-12. Started the car, no compressor- jumped the low pressure switch- on my 90 it is the sw closest to the evaporator (near the firewall) the single sw on the low press line, mine has 2 sw downstream of the orifice tube- those are the hi press lines. Still nothing- what the heck??? found and checked the a/c fuse- on mine under the radiator tank on pass side- everything good, all fuses in fuse box good- even replaced the a/c clutch relay under the drivers side dash- (cause it was missing cause I took it out last year to prevent any damage to the compressor in case the clutch kicked on.

Then someone on the forum said to disconnect the battery for 10 minutes, jump the low press switch and start it back up.

And guess what- just by disconnecting the battery, it reset whatever needed to be reset and now I have COLD air in hot, humid Louisiana!

Disconnect the battery, jump the low press sw and charge your system.
Good luck!
AAIIIEEEEEEEEEEEEE! Pass the Gumbo!

 

I even put 12 volts to the a/c clutch witht eh engine running to make sure it was operational.

After re=reading your last post, ours are set up the same.

Try the battery disconnect!

 

You need to jump the low pressure switch which is on the evaporator outlet. The switch is on the top line right where the line comes out of the evaporator. Then disconnect your battery for a few minutes as the '90 and up models need to be reset. Reconnect the battery and you should be ready to charge.

 

I'm sorry its by the evap coil, I was thinking of my truck..

 

Sammy Calderone had the same thing. all he did was put the switches back in the circuit and then did the battery thing and I think it worked for him

 

Thanks Guys!!! I'll ry it tomorrow after work. I appreciate the help.
Let you al know of the outcome later.