A question for you A/C guys...

[Rumble]

I've been updating the a/c system on my '79 Cadillac CDV, and I'm almost ready to add the refrigerant. Car was originally equipped with an A6 compressor. That's been changed to a modern style 4Seasons aluminum compressor.

So here's my question, the shop manual says to "disconnect the low pressure wire" (did that), and then add a "jumper wire between the terminals of the harness." Would this be the harness connector that plugs into the compressor?

 

[Thermo1223]

No they want you to trip the low pressure sensor so the compressor runs as you add refrigerant if you are paraphrasing correctly. Basically letting the compressor "suck" it in.

 

[Chris142]

They want you to bypass the low side pressure switch. If you had a charging station you could skip that step. Remember that the compressor is lubed by the oil in the refrigerant and running it with a low charge starves your new compressor of oil.

 

[Rumble]

I think for today I'll just to a vacuum and test for leaks. I'm not going to tackle the refrigerant until I know exactly what I'm doing. There's 5+ ozs of oil in the compressor, and 5+ ozs in the accumulator. I'll be using R-134a. The original system used 3-3/4lbs of R-12 (60ozs). I was figuring on putting in 4 "12oz" cans of refrigerant which would be 48ozs, or 20% less than the old system used.

I don't want to hurt the compressor by starving it of oil. Is this too tricky using the can method?

 

[440Magnum]

Your fill calculation sounds about right. Since you say you're using a new compressor, I assume you also flushed the evaporator and condensor to get rid of all the old R-12 oil and chlorinated residues. Even though most currently-sold compressor oils will tolerate R-12 residue way better than the early days, I still like to get rid of ALL of it (and all the old oil as well) so that the system is truly empty and you don't have undissolved mineral oil somewhere occupying volume that should be available to refrigerant.

 

[Fleetmon]

I'm sure you added compressor oil to the compressor when you installed it. The next step would be to pull a good vacuum and afterwards install the first can as a liquid into the discharge (high pressure) port with the enigne OFF.

That is not a good practice to jump a compressor to add refrigerant.....as Chris142 says, doing it "their" way is a sure method of starving the compressor of oil. It takes a while for the comp oil you added to mix with the refrigerant and circulate through the system. A charging station will do it all at once but if you're doing it by cans, I would certainly introduce the first can as a liquid in the high side.

 

[Rumble]

Originally Posted By: 440Magnum
Your fill calculation sounds about right. Since you say you're using a new compressor, I assume you also flushed the evaporator and condensor to get rid of all the old R-12 oil and chlorinated residues. Even though most currently-sold compressor oils will tolerate R-12 residue way better than the early days, I still like to get rid of ALL of it (and all the old oil as well) so that the system is truly empty and you don't have undissolved mineral oil somewhere occupying volume that should be available to refrigerant.


Yes, I thoroughly flushed the evap/condenser and lines. Installed new comp, accumulator, orifice valve. I'll be using ester oil. Didn't mention earlier, but I have gauge set and new vacuum pump. Thanks.

 

[Rumble]

Originally Posted By: Fleetmon
I'm sure you added compressor oil to the compressor when you installed it. The next step would be to pull a good vacuum and afterwards install the first can as a liquid into the discharge (high pressure) port with the enigne OFF.

That is not a good practice to jump a compressor to add refrigerant.....as Chris142 says, doing it "their" way is a sure method of starving the compressor of oil. It takes a while for the comp oil you added to mix with the refrigerant and circulate through the system. A charging station will do it all at once but if you're doing it by cans, I would certainly introduce the first can as a liquid in the high side.


That was the method I was going to use, first can in high side with engine off. Yes, I added the oil in comp/accumulator. Thanks.

 

[440Magnum]

Originally Posted By: Rumble
Originally Posted By: Fleetmon
I'm sure you added compressor oil to the compressor when you installed it. The next step would be to pull a good vacuum and afterwards install the first can as a liquid into the discharge (high pressure) port with the enigne OFF.

That is not a good practice to jump a compressor to add refrigerant.....as Chris142 says, doing it "their" way is a sure method of starving the compressor of oil. It takes a while for the comp oil you added to mix with the refrigerant and circulate through the system. A charging station will do it all at once but if you're doing it by cans, I would certainly introduce the first can as a liquid in the high side.


That was the method I was going to use, first can in high side with engine off. Yes, I added the oil in comp/accumulator. Thanks.


In that case you should be fine. The first can will pressurize the system enough to at least let the compressor cycle as the other cans go in, and to keep the oil moving where it should.

 

[DBMaster]

May I ask for a URL to see the compressor you purchased to replace an A-6? I miss my 72 Pontiac's A/C. I could achieve vent temps of 31 degrees. And, the car still had it's original compressor at 212,000 miles - albeit with a new clutch assembly. The good old days.

 

[Rumble]

Originally Posted By: DBMaster
May I ask for a URL to see the compressor you purchased to replace an A-6? I miss my 72 Pontiac's A/C. I could achieve vent temps of 31 degrees. And, the car still had it's original compressor at 212,000 miles - albeit with a new clutch assembly. The good old days.


It's available at O'Reilly's, under the "Murray" brand. Bonneville/GP is showing part #58089, you will need to key in your exact model & engine etc.

 

[DBMaster]

I found it. It actually looks like an A-6 made out of more modern materials. It is the one that would have fit my 72 Pontiac, if I still owned it. If it is half as durable as the original it will be a good deal for the price.

 

[Rumble]

Got it charged. For some mysterious reason my a/c fuse blew while charging the 2nd can. Having a near heart-attack, I continued once I got that sorted out and got it cooling fine. It was getting dark, so I'm going reconnect the gauges tomorrow and check the pressure numbers. Thanks for all the help/advice everyone!

Got a question though, only used about half of the last can, if I close the can tap, can I disconnect it from the hose and save the rest (leaving the can tap valve on of course)?

 

[artificialist]

Originally Posted By: Rumble
Got a question though, only used about half of the last can, if I close the can tap, can I disconnect it from the hose and save the rest (leaving the can tap valve on of course)?

No.
Leaving the can screwed into the hose is the only way to store the remaining refrigerant.

 

[Rumble]

Originally Posted By: artificialist
Originally Posted By: Rumble
Got a question though, only used about half of the last can, if I close the can tap, can I disconnect it from the hose and save the rest (leaving the can tap valve on of course)?

No.
Leaving the can screwed into the hose is the only way to store the remaining refrigerant.


OK, thanks.

 

[zzyzzx]

On every car I have done there was no need to do that. The pressure from the can will be enough to force the refrigerant into the system and enough to trip the pressure switch so that the compressor turns on.

 

[440Magnum]

Originally Posted By: artificialist
Originally Posted By: Rumble
Got a question though, only used about half of the last can, if I close the can tap, can I disconnect it from the hose and save the rest (leaving the can tap valve on of course)?

No.
Leaving the can screwed into the hose is the only way to store the remaining refrigerant.


I store unused R-134a with the can tap installed and closed (no hose) all the time. Of course how long it will last depends a bit on the quality of the can tap- a tap with a cheap valve or a crummy seal at the can will leak, but an open hose sure isn't going to save any refrigerant either. I can only see that working if the hose has a (good quality) positive shut-off valve.