Dano86

Problem: 1992 Vette air conditioner not working. Has been converted to 134

Signs and symptoms:
1 only hot outside air coming in. compressor not cycling. I can get it to cycle and will cover that in a minute.
2 C68 test under 00 gives me code 9 (low freon)
3 when I hook up the lines to test the pressure I get a way high reading (100+ psi should be 45-50 with ambient temp at 80).

So I tried, out of dumb curiosity, to drain a little out (successful). Got the pressure to 47ish psi, pulled the courtesy and radio fuse to reset per owners manual. Start car compressor starts cycling like it should but no cold air. After about a min or two compressor stops. Light starts blinking and pressure in the lines is back over 100psi.

I am completely lost! What are your thoughts??

Thanks
Dano

Just BOB

Blocked screen on the orifice tube? Desiccant bag in the accumulator may have ruptured or seals on compressor pistons may be "shredding".

Dano86

First off thank you for the reply!
I am glad that you said orifice tube that was the guess of the parts store also and for 2 bucks well worth the try. the things i have seen on youtube all call for a special tool to remove the line any way around this or is this something that most parts stores have available do you think?

I have not done much when it comes to AC units but I do enjoy learning and the since of accomplishment when it is all done.

thanks again

Just BOB

There is a special tool for orifice tube removal (actually 2 different lengths, depending on application) Many of them can be grabbed and pulled out with needle nosed pliers. The tube is in the high pressure inlet tube of the evaporator. Just unbolt the high pressure liquid line coming from the outlet side of condenser.

Churchkey

Probably low on Freon. The compressor needs to be running to check pressures.

Vehicle in the shade or indoors.
I run an electric box fan blowing at the condenser.
Hook up gauges.
Windows up, doors closed.
Engine rpm 1500.
ATC temp set to 60 degrees & recirculate. max blower speed.
Hot wire compressor to run.
Let the system normalize for a few minutes.
Low side pressure should be 28# when 70 degrees ambient.
30# when 80.
32# when 90.

Add Freon if the low side pressure is lower than stated.

If pressure is high there is a restriction/problem in the system as advised.

After charging reset the ATC you should be good to go.

Techs may use a different system to check but the above works.

Good luck.

Dano86

OK I replaced the orifice tube tonight (old one did not look bad at all).
To check on my thinking and understanding, you can only read the pressure when the compressor is cycling on correct?
Also how do you "hot wire" the compressor to continually run? Can refrigerant only be added when it is cycling on?

Churchkey

When checking pressure you want the compressor running all the time not cycling.

"Also how do you "hot wire" the compressor to continually run?"

Remove the black E connector from the low pressure switch located in/on the larger aluminum tube exiting the evaporator case. Make a jumper wire, Male spade connecter, a length of wire connected to battery +. If your vehicle wire color codes are the same as mine insert the male spade into the terminal in the e connector with the blue wire going to the compressor clutch. The clutch should engage. Add Freon through the low side port. When you reach the above listed pressure (post 5) don't add any more Freon. Remove jumper wire & connect low side E connector to the low side switch. At this point the compressor probably will not cycle. The ATC panel will need to be reset. Shut off engine, disconnect the negative battery terminal for a few minutes. Re connect battery, start engine, set AC controls = good to go.

"Can refrigerant only be added when it is cycling on?"

No however to charge the system without running the compressor you need an AC charging/recovery station. If you happen to have a charging station I doubt this conversation would have taken place

SunCr

Sounds like you have air in it now so you need to start over and replace the Accumulator because if it hasn't fallen apart, it will once it's exposed to the atmosphere. Then the correct charging procedure starts by evacuating all the air or pulling a vacuum with a vacuum pump. When you go to charge, the vacuum will pull in the first can. You can then jumper the Low Pressure Switch Harness Connector with a paperclip which will keep it running while you add the remaining charge.

You need the high side along with the low. It's easier to see a restriction on the high. A scan will pick up that number from the Pressure Sensor and if it only reads voltage; 1 volt equals 100 psi.

R134 at 80 degrees is about 77 psi so a little engine heat could have resulted in the static reading you got on your gage. If you want a more precise number, put the end of a 5 Buck Digital Thermometer on any line and compare the readout to a pressure/temp chart. Unfortunately, that isn't going to work if there's air in it (but when the pressure on the chart doesn't match the temperature on the thermometer, it will confirm that something other than R134 is in it).

A 100 on the Low (with it running) is usually because there's a hole in the Orifice - or no Orifice. 50 psi on the low - with it running - cranks out 60 degrees from your Center Vent. If it's a 100 or so, that may be the best it can do, but I'd aim for a lower number. Consider having your PCM reflashed to turn on the fans with a high of 170 psi. Right now, nothing is cranking until the 220's and R134 can zoom into the 300's if you don't start chilling it at a lower pressure/temp.

Churchkey

If the AC panel has a flashing light a paper clip across the low pressure switch connector to run the compressor will not work. When the panel is flashing there is no power to the low side switch. When the system is fully charged & the ATC has been reset by disconnecting the battery for a brief period the low side switch will then have power.

On 89 & earlier model cars the low side pressure switch may have power at all times when AC is selected & compressor function operates solely on the pressure switch.

90 & up models require a separate 12v feed to run the compressor until the system is full.

SunCr

Clearing the Code and jumpering the Harness completes the Circuit. Low Gas is set by monitoring on/off (compressor relay) generated by the Low Pressure Switch and for a rise in Pressure/Voltage from the Pressure Sensor when the clutch engages. If it doesn't engage, the fault is the Pressure Sensor or most often, no gas at all.

Dano86

Good info. Thank you!!! I am looking around to see if I can find a pump to drain and charge today
Thanks again!!!

Dano86

Here we go. I added a can of 134a, the hard way by reseting the A/C system three times before it had enough to keep running. It is low on psi (needing another can still) but blowing cold air!!

I do have a couple more questions if you have answers that would be amazing!

Is there a way to check the oil level. Here is my thoughts, the system may lose refrigerant but what about the oil? Can I add too much oil by using only the cans with oil added?

Thanks to everyone for their words of wisdom!!! I now have cold air, somewhat

HAPPY FOURTH!!
Dano

Just BOB

It somewhat complicates things that you are dealing with an R12 system that has been converted to R134. I take it you have no insight into the conversion that was done.

Oil primarily accumulates in two places in the system, the compressor and the accumulator. I have read articles that say the the R12 refrigerant oil in the compressor needs to be removed to the greatest extent possible. One article went so far as to say that the compressor should be removed and drained, filled with the appropriate dose of R134 oil, evacuated, charged, run for a short period, then removed and drained again. Twice, for a total of three exchanges. I have also read that R134 systems are sensitive to overcharges of oil (and/or dye). The oil is more prone to absorb moisture, which really messes with the compression/expansion cycle dynamics. I'd look it up to verify, but if I recall, GM systems use PAG oil. One other data point: When charging by weight, a good rule of thumb is to use 80% of the R12 charge listed for the system you are converting.

BUT, to answer the question, one can of R134 with oil in it probably isn't going to cause a problem. Not knowing whether the compressor has an adequate amount of the correct oil is the real concern.

SunCr

There's no dipstick so who knows - AND who knows what's in it. If you were to change out the Accumulator, you would drain what's in it and add that back plus an ounce. You could also use a synthetic compatible with either oil.

If you haven't done that (replaced the Accumulator) or drawn a vacuum; there's air in it, so don't jumper the compressor by applying power from the hot side of the Relay or any other source (that was suggested by someone else). Air or anything other than the refrigerant that's in it, can effectively double operating pressures and using anything but the Controls to run the Compressor takes the High Limit - in this case the Pressure Sensor - out of the picture. It's designed to shut down at 400 psi. At 600 psi, the relief valve let's go (you hope). Anything above that blows a hole in something. What's spurting out immediately flashes to it's atmospheric temp or about -15 degrees for R134. That hurts.

corvetero

Could somebody tell me what is the weight of R134 to be charged in a 92 system.

I know is about 80% of R12 capacity, but I don't know what is the R12 weight for my car.

Thanks in advance.