88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
When an r-12 system is NOT turning the compressor the lowside pressure is around 70-90psi ( depending on the system and inital charge and temp)
The middle line I have modified ( read kluged) an adaptor for the F-12 replacement.. and I have incorporated a cheepo gauge in the feed line to tell me how much pressure I have in my feed can or Jug..or If I have an OVERPRESSURE situation.
The HIGH side line ( right gauge... yellow line with an adaptor ,right hose with red adaptor)
is for the following.. GM changed the size of the high side fitting to keep people from trying to charge off the HIGH side with the car running. Those pressures could/can reach 300psi and could turn one of those freon cans into a NICE GRENADE.
Very good and very well laid out lesson. I would hope that one would look further into the proper oils, evacuation and other issues in addition to the above basics before taking on a major project.
I would like to add my opinion regarding refrigerants. If you have an R12 system, even at $29 per pound, the least expensive major component in that A/C is the R12 refrigerant.
Some cars convert reasonably well to R134a. One of those cars is my '88 Vette with Nippondenso compressor. It makes 45 degree vent temps and will freeze you to death. I expect that at least part of the reason is that there is a small amount of cabin volume that must be cooled, additionally the Nippondenso handles the conversion well. I expect that GM was looking forward to the R134a and started using components that were compatible, that's why the change to the Nippon.
Not all original R12 systems convert well. A York compressor cannot handle the extra pressure. Many Foreign cars that were not really designed for extreme heat, do not have any reserve cooling capacity that can allow for the 15% or so loss in cooling capacity when converting to R134a. Some of them don't convert well even after adding a larger or parallel flow condensor.
For those original R12 cars that convert well, like my Vette, it makes sense to convert when it comes time to do a repair and recharge. There is no sense in converting a working system.
For those cars that do not convert well, repair any leaks, recheck thoroughly to ensure that there are no leaks, pull a deep vacuum and recharge with R12. You will ensure the health of the A/C, obey the law, and continue to be cool.
Beware of "drop in" replacements. Most of them are either explosive (illegal) or blends. Whenever there is a leak in a system containing a blend, the different components will leak at different rates. The only way to correctly restore the proper blend is to repair the leak, evacuate and recharge.
Again, even at $29 per pound, R12 is the least expensive major component in the system. You can go online and take an open book test for $15. After passing this test, you will be 609 certified and can buy all the R12 you like, legally. At that point, you can use vigmans excellent tutorial above and keep cool.
I think there is also an R-12 substitute available. It's called Freeze-12 (sp), it's fully compatable w/R-12 systems, and doesn't require EPA-609 certification to buy. I've never used it, though, so I couldn't tell you if there are any drawbacks.
Freeze 12 is one of the alternate refrigerants I was referring to. It is the most common of the alternative refrigerants. I don't know if it is explosive or a blend, but it is one or the other. The disadvantages for each are described in my post above.
My biggest worry about the use of alternative refrigerants is the contamination of our R12. All we have is what is on the shelf, not yet used, and what we can recover without contamination from existing systems. Every time one of these alternatives is put in a car, we risk contaminating the R12 that is being recovered every day.
If you have an R12 system, it may not seem so at the time, but unless it is one that will convert well to R134a, R12 is clearly your best bet. Even at $29 per can, it is the least expensive major component in your R12 air conditioner.
Please don't contribute to the contamination of our remaining R12 supply by using one of these refrigerants. You are also endangering the health of your own a/c system due to the question about compatible oils.
I saw that low side pressures when the compressor is not runnng should be 70-90 psi, but what should the high side read?
If my compressor is not cycling off (on all of the time), does that just mean that the pressure has not shifted? Should I be concerned?
When the compressor is not engaged, the high and low side pressures will begin to equalize. After a few minutes without the compressor running you will read about 80 pounds regardless of whether the system is fully charged or only has one ounce of liquid.
Therefore pressures without the compressor running are virtually meaningless.
Thanks for your reply. What should the low and hi side pressures read for an optimally charged system when the compressor is running? I read and understand in Vig's post that the compressor cycles at ~40 psi as pressures shift, but the compressor in my '84 never seems to shut off.
This will depend on many things. To begin with, are you still using R12?
Whatever the refrigerant, you need to begin by stabilizing the pressures. To do this it would be good to have a high volume fan in front of the condensor to simulate highway speed ram air. Run the engine at about 2000 RPM with a/c turned on max, for about five minutes.
If under these conditions, you continue to show 40 PSI on the low side, you may be overcharged. If the system is cooling okay, then see that the high side does not get too high. If it is not exceeding 300 or 310 then just use it for awhile and see what happens. Do not release the refrigerant to the atomosphere to lower the charge. If you MUST remove some of the charge, take it to an a/c shop and have them recover some.
Let us know what refrigerant you are running and what the pressures are after they have stabilized.
I've got an 89. I noticed the air conditioning didn't work when the car was not moving. I found that the cooling fan is not working. I've traced it to the switch on one of the refrigerant lines. I disconnected the wires and the fan turns on. Someone said this may be fitted with a shrader valve but the connection on the manifold doesn't seem long enough to have one. Any ideas?