Fresh AC Charge - R12

[SteveZ82]

I've been searching the forum for weeks and got so much info on charging my 86 GN ac system. I just have a couple of followup questions as I'm not used to these older R12 systems. My friend is an HVAC specialist and was helping me out. We found that the high pressure schrader valve had a slight leak so replaced that. More on that in a sec. I have an older yellow jacket gauge set and got into 6 cans of R12 for free. Sweet. I put the low side fitting on but the high side fitting on the high pressure line was too small for the gauge. I found that weird so I'm curious if the line was replaced at some point. There was no indication of this being converted as the accumulator is original. Anyway, we vacuumed the system from the low side. Did that for an hour and it held vacuum for 20 minutes. We then sucked in 2 12oz cans of R12 and one 14oz can. Started the car and the compressor wouldn't turn on. Low side was getting up in pressure to like 85 psi. It dawned on me that the switch on the accumulator needed to be adjusted so we adjusted it out until the compressor engaged. I have a digital ac/heater control (C68 code) so we had it on bi-level and pegged all the way to 65 degrees. The low side pressure was at about 40 psi so we started to add some more r12. Probably about another 6oz. The vents got down to about 49 degrees and the low side pressure stays at about 35 psi now. At 44 oz of R12, I think we are still a bit low as the system calls for 3.25 lbs (52oz). Here are my questions:

1) Compressor doesn't cycle. Stays on constantly. I've heard mixed opinions on this that it should always stay on and some say it should cycle so I don't know. I know my newer car cycles but that's 30 years of technology. It was in the 70s last night
2) Accumulator is soaking wet with condensation and one of the high pressure lines is as well. Is that normal?
3) High pressure lines. One line is ice cold and the other is super hot. I heard that could be because it's under or overcharged or is this normal?

Anyway, AC works just have these question to be sure I don't damage the system in some way. I only plan to run ac when really needed. Black cars in the summer heat...you know what I mean.

We followed this guide: http://www.gnttype.org/techarea/airconditioning/ac101/trblsht.html

 

[mommasGN]

Could use a little more charge but it all sounds normal to me. Compressor will cycle when it needs too. Both of the lines running across the top of the radiator are not high pressure lines...... one is the discharge (high) side, the other is the suction(low) side. So yes, one should be hot and one should be cold.

Congrats on getting the r12. That stuff cools a lot better!

 

[SteveZ82]

Could use a little more charge but it all sounds normal to me. Compressor will cycle when it needs too. Both of the lines running across the top of the radiator are not high pressure lines...... one is the discharge (high) side, the other is the suction(low) side. So yes, one should be hot and one should be cold.

Congrats on getting the r12. That stuff cools a lot better!

Thanks for the reply! I thought so but wanted to be sure. I love this forum. Great owners of these cars. I never expected that when I bought this car after drooling over them for years. Thanks again!

 

[RmvBfrFlght]

To connect to the high side fitting need an adapter. GM started changing the high side fitting as too many people were trying to charge the system via that fitting (doesn't work). Note that these adapters are difficult to get/find.

On a side note I rarely connect the gauge set to the high side. Too much oil & refrigerant is lost on the connect/disconnect. Only required to see the high side if troubleshooting an issue. Be sure to use a good cap on the high side fitting.

Hook gauge set to the low side, fill, and check the low pressure cycling switch psi.

RemoveBeforeFlight

 

[SteveZ82]

To connect to the high side fitting need an adapter. GM started changing the high side fitting as too many people were trying to charge the system via that fitting (doesn't work). Note that these adapters are difficult to get/find.

On a side note I rarely connect the gauge set to the high side. Too much oil & refrigerant is lost on the connect/disconnect. Only required to see the high side if troubleshooting an issue. Be sure to use a good cap on the high side fitting.

Hook gauge set to the low side, fill, and check the low pressure cycling switch psi.

RemoveBeforeFlight

Ah. Didn't know that. When you think you know your car... Anyway, thanks for the tip. As I scratch my head, how do you check the low side pressure switch psi? I assume the psi is the same on the low side port as it is at the switch since they are both on the accumulator? I had to adjust the switch out about a half turn to get the compressor to kick on and now it just stays on and stays at about 35 psi on the coldest setting.

 

[RmvBfrFlght]

On the gauge set face should be not only the pressure, but an R12 and a R134 scale that shows the temperature. 35 psi may be a little high for R12, but this also depends upon the ambient temperature and engine RPM.

2K RPM is the typical engine RPM for checking the system. Once the low side pressure drops below 30 or so psi the pressure switch should cycle the compressor off. This prevents the evaporator from freezing.

Then as the pressure increases the switch should cycle the compressor back on.

RemoveBeforeFlight

 

[SteveZ82]

On the gauge set face should be not only the pressure, but an R12 and a R134 scale that shows the temperature. 35 psi may be a little high for R12, but this also depends upon the ambient temperature and engine RPM.

2K RPM is the typical engine RPM for checking the system. Once the low side pressure drops below 30 or so psi the pressure switch should cycle the compressor off. This prevents the evaporator from freezing.

Then as the pressure increases the switch should cycle the compressor back on.

RemoveBeforeFlight

Good to know. it was at idle and on a ride continued to stay on. I think I have to adjust my pressure switch for the lower psi so the pump cycles. Thanks for the reply. It was about 70 last night as well.

 

[ScottHeidinger]

There is a adapter for the high side port. The R12 hose never fit directly on the automotive port without a adapter. Try to put the low pressure switch back where it was before you turned it. At 70 degrees with R12 35 psi on the low side sounds a bit high. Once you get the pressure switch adjusted see what the pressure is at 2k rpm. It’s good to know both the high and low side pressure so I would get the adapter so you can see if you have problem.

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[Frederickdav]

My AC died the summer after I bought the car. I've been tempted to change to R134 but then I would only use it a couple of times a year. Would it be worth the cost and bother?

 

[ScottHeidinger]

I’m in Florida. I would probably drive my car about 4 weeks per year if it didn’t have ac. I’m too old and it’s too hot. I drive it daily and only turn the ac off if there is a really fast car in the other lane at a red light. I leave the ac on for the diesel trucks that want to play.
I would start by figuring out what’s wrong. I’ve seen people drive around for years with no ac because a low pressure switch went bad. If the compressor ate it then it gets expensive.


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[SteveZ82]

We did find the high side schrader valve was stuck open. Replaced that and vacuumed the system. It held vacuum for a while so we filled it with about 44oz. The pressure on the low side is high when the compressor isn't running at idle. Like 70 PSI. I'm going back to the garage on Saturday, I'll throw the gauge back on, warm the car up, turn on the AC, set the pressure switch to turn off and set it to 2k RPM. Learning a lot. Usually, on my r134a cars, you just fill it and go. But want to do it right, don't want to worry about a bad compressor.

I followed this article http://www.gnttype.org/techarea/airconditioning/ac101/trblsht.html and stopped at 35 psi.

 

[ScottHeidinger]

What is the high side reading?


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[SteveZ82]

No clue. Don't have the adapter. Which is why we charged it lower than spec.

 

[SteveZ82]

What is the high side reading?


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No clue. Don't have the adapter. Which is why we charged it lower than spec.

 

[ScottHeidinger]

I highly recommend buying the adapter. You really need to be able to see high and low pressures to insure there are no issues or to properly diagnose any issues that may exist.


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[SteveZ82]

I highly recommend buying the adapter. You really need to be able to see high and low pressures to insure there are no issues or to properly diagnose any issues that may exist.


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Doing that. My maintenance scheduled for this weekend has been post-poned for a couple of weeks so I have time. I don't drive it every day. Just fixing some odds and ends since almost everything is original on it and it sat for a long time in a garage.

 

[SteveZ82]

Doing that. My maintenance scheduled for this weekend has been post-poned for a couple of weeks so I have time. I don't drive it every day. Just fixing some odds and ends since almost everything is original on it and it sat for a long time in a garage.

Well, a new development on this. I think my pressure switch is on teh way out or the connection is a bit finnicky. I don't have the high pressure adapter yet but decided to check low side at around 2000 RPM with the compressor engaged and I sit at around 32 PSI. However, I really need to f*ck with the switch to get it to engage so I may order a new one. I literally have to plug it in just right to get it to work. Any pointers on the correct part # and will replacing it leak out all the R12 we put in or is there a cut off at the switch or a schrader valve?

Kirban's has this one. https://www.kirbanperformance.com/p...lco+AC+ACCUMULATOR+SWITCH+&+O-RING+#7769.html

 

[salvageV6]

Kirbans is a good one, it will spritz for a second but there is a valve in there so no big leaks.

Local parts stores should have a usable one as well if you want to work on it quicker.

 

[SteveZ82]

Kirbans is a good one, it will spritz for a second but there is a valve in there so no big leaks.

Local parts stores should have a usable one as well if you want to work on it quicker.

Ok. Thanks. It’s on order and I’ll throw it on this week. Thanks for all the help. Ac got down to about 47 degrees on an 85 day at about 60% humidity so hopefully it’ll stay that way.

I will also say, my static no engine running low side pressure is 90psi which to me seems high. My HVAC guy said that’s normal but not normal with the ac running.

 

[Ttype6]

Ok. Thanks. It’s on order and I’ll throw it on this week. Thanks for all the help. Ac got down to about 47 degrees on an 85 day at about 60% humidity so hopefully it’ll stay that way.

I will also say, my static no engine running low side pressure is 90psi which to me seems high. My HVAC guy said that’s normal but not normal with the ac running.

Typical high and low side pressures are 150/35 respectively. When the compressor
stops turning,the high and low sides equalize due to internal leaks. The middle point between these 2 numbers is about 90 psi. When the compressor starts up again,the low side pressure will fall and the high side pressure will rise. Your system produces very cold air and the pressures sound right. Are you planning on screwing with it until it doesn't work as well as it does now?