im trying to convert my 91 to the rf 134 refrigent from r12,,i changeed the connection and i cand put the refrigant in,i guess because the ac compressor clutch is no engaing,is ther a way to make it so it will start to take the refrigant?

 

If you are just going to shove 134 into your R12 system , you may have some problems down the line.

But if you insist, you will need to pull a vac. and short the low pressure switch in order to load the gas.

On some cars in the early 90's shorting the switch still didn't let the compressor engage.

I haven't tried it on the Vette so I am not sure.

 

R12 system on my 90 was low- low freon code- I pulled a vac, and hooked up the r12, turned the unit on and the compressor did not engage. I let it sit there at high idle about 15 minutes, tried jumping the switches, no help, after about 15-20 minutes the compressor kicked on for a few seconds, kicked off, kicked on again, and after about 5 minutes had enough freon to "make the switch" and then the compressor ran as it should while I filled it with r-12. Since I have a leak and haven't found it, I haven't messed with it, or rebuilt the compressor, converted to r134a, etc. r-12 is $36/can with my friends EPA license at the local auto parts store.

 

yes,i cant buy r12 so im changing ,i opened the system and vacumed it and added oil,now im tryine to ad rf134a....thanks

 

trying to charge my 91 vette,,i have the can ready ,the clutch wont engage,,i shorted the plug on the low side,,nothing,,,,i unpluge the two wire plug on the low side ,with a vom meter looking in the system i see a short,,looking at the plug in my hand i see an open,,,help,,what should i see,how can i engage the clutch to add refrig,,thanks

 

Did the system ever work with R12?

 

yes,worked good ,,but didnt use the ac for 3 monts,,

 

I'm not sure what you've done, but I hope you don't blow it (and yourself) up. Anyway, nothing is going to work as long as there's a Low Gas Code - so get rid of it by disconnecting and reconnecting the battery. To charge, let vacuum pull in the first can and that should give it enough - with the Low Pressure Switch harness jumpered - to suck in the balance of the charge once you start it up and not reset the Code. Monitor the high side on your Manifold Gage Set and stop when it reaches 2.2 to 2.5 times the temp of the air across the Condensor. When done, put it on high and disconnect the Blower Motor while observing your Low Pressure Gage. That will drop the Low side and the Compressor will cutout. Note that Pressure. Since R134 has a freezing temperature a couple degrees less than R12, you want the switch threshold set to 22.5 psi. If it cut out higher (for R12 it's set to 25 psi), there's a screw between the switch terminals. Turn in counterclockwise to lower the threshold; clockwise to raise it. Go 1/2 turn at a time and retest.

 

I have a 90 so I don't know if it is the same as your 91.

Did you check the fuse?

 

please understand,im a electronic tech retired by i know nothing about ac,,i bought a can of refrig and a hose with a gage on it from autozone,,,ok,thanks,i now have cold ac,,i put about a can and a half in it ,,blowing ice cold,,i dont understand about a screw you talked about,,can you explain anything else i need to do,with what i have,,the engine seems to be running alot higher now with it on,,,

 

Not knowing can be a little hairy - if not dangerous. If it's cold, leave it alone or take it to a shop where they can leak test it because if it was empty when you started, it'll be empty again.

 

take it to the shop? no dealer or shop is willing to work on 20 year old cars around here,and isnt this is what corvette forum for,,,thanks its fixed

 

There's no way to force feed it in your driveway - nor is it the best method, though at the Factory it did get a suck and dump. A decent vacuum will draw in 12 to 16 ozs, but that's it.

'90 and up are ECM controlled which drives (grounds) the compressor relay. If a High Side Pressure Sensor is installed (can't remember if '90 got it. but I'm pretty sure the '91 did), the ECM needs to see something around .8 volts static (about 80 psi and a couple of ounces will give it that much) and then an increase in that voltage (pressure) after engagement to do it's thing. It's also monitoring the Low Pressure Contacts (ground side) for how often they open/close as a means of determining charge. Frequent open/close and/or no increase from the Pressure Sensor kills the Relay ground and sets the Code and it isn't going to do anything until it's cleared. And even if cleared, it can reset until you meet the static condition for engagement; ie, if the Sensor is sending 0 volts/pressure, it ain't gonna work until vacuum sucks in some ounces no matter what you do with the Low Pressure Switch.

All C4's use the cycling orifice system. C5's and C6's switched to the constant run, variable stroke compressor, which is a somewhat different ballgame as it eliminates the low pressure switch, but relies on a Pressure Sensor for everything else. For ours, it's out from the Compressor to the Condensor to and through the orifice to the Evaporator, pass the Low Pressure Switch and onto the Accumulator and then back to the Compressor.

 

I believe you are also supposed to replace the drier, orifice, orings, and flush the system. Then put the vacuum on and convert.