Automotive Air Conditioning Information Forum

I have a 1968 Buick Electra with factory AC. The cooling is not good at all. Low pressure is around 28 and hi pressure (from the comprrssor) is 110. Temp is around 70 F. Could the compressor be bad or the expansion valve? Im quite new to this.

I can feel that the gas commin out from the compressor that goes to the condenser is varm. The metal lines coming out of the evaporator is quite cold. Temp of air in car drops maybe 10 degrees or less when its 70 F outside.

You need to find a shop that services R-12 refrigerant; they would have equipment to pull out the remaining R-12 and weigh it, to determine how low your charge is.

From your pressure readings and that your high side line is only warm and not hot, plus your pressures (if measured at about 2000 rpm) indicates you have lost refrigerant over time.

Cusser wrote: Sat Jul 04, 2026 6:19 am You need to find a shop that services R-12 refrigerant; they would have equipment to pull out the remaining R-12 and weigh it, to determine how low your charge is.

From your pressure readings and that your high side line is only warm and not hot, plus your pressures (if measured at about 2000 rpm) indicates you have lost refrigerant over time.

Thanks

Whats the differende between a low charge and a bad compressor. I try to undestand the problams. Its not easy to find a shop where I live that can service old systems. They need instruktions.

Does your car still have R-12 and a Sight Glass on top of the Receiver Dryer? If so, and you have on hand or can still purchase R-12 refrigerant, you can do it yourself the simple, old-fashioned way without a shop's intervention, presuming you have a Manifold Gauge Set (MGS) with the proper fittings and a tapper valve that pierces R-12 cans.

Chances are, the system is low on refrigerant, as Cusser suggested. Check the Sight Glass while the system is running at about 1,800 engine RPM. If you see bubbles or just streaks of oil, then the system is definitely low.

Add refrigerant (be sure to purge all the MGS lines of air) until the bubbles just disappear. It might take two or three cans to recharge the system properly depending on how low it is.

You should now have nice cold air again with good pressures. If not, then the system has deeper issues that will require additional diagnosis and leak testing.

JohnHere wrote: Sat Jul 04, 2026 9:56 am Does your car still have R-12 and a Sight Glass on top of the Receiver Dryer? If so, and you have on hand or can still purchase R-12 refrigerant, you can do it yourself the simple, old-fashioned way without a shop's intervention, presuming you have a Manifold Gauge Set (MGS) with the proper fittings and a tapper valve that pierces R-12 cans.

Chances are, the system is low on refrigerant, as Cusser suggested. Check the Sight Glass while the system is running at about 1,800 engine RPM. If you see bubbles or just streaks of oil, then the system is definitely low.

Add refrigerant (be sure to purge all the MGS lines of air) until the bubbles just disappear. It might take two or three cans to recharge the system properly depending on how low it is.

You should now have nice cold air again with good pressures. If not, then the system has deeper issues that will require additional diagnosis and leak testing.

Thanks!

R12 is not legal in my country so I cant búy it.

I did check pressure in system this morning with engine on. It was 72 F and system pressure around 73-74. That indicates that I have enough refrigerant. Someting else must be wrong. Coluld it be a bad compressor or an expansion valve? I dont know how to figure out what it is.

JohnHere wrote: Sat Jul 04, 2026 9:56 am Does your car still have R-12 and a Sight Glass on top of the Receiver Dryer? If so, and you have on hand or can still purchase R-12 refrigerant, you can do it yourself the simple, old-fashioned way without a shop's intervention, presuming you have a Manifold Gauge Set (MGS) with the proper fittings and a tapper valve that pierces R-12 cans.

Chances are, the system is low on refrigerant, as Cusser suggested. Check the Sight Glass while the system is running at about 1,800 engine RPM. If you see bubbles or just streaks of oil, then the system is definitely low.

Add refrigerant (be sure to purge all the MGS lines of air) until the bubbles just disappear. It might take two or three cans to recharge the system properly depending on how low it is.

You should now have nice cold air again with good pressures. If not, then the system has deeper issues that will require additional diagnosis and leak testing.

Thanks!

R12 is not legal in my country so I cant búy it.

I did check pressure in system this morning with engine on. It was 72 F and system pressure around 73-74. That indicates that I have enough refrigerant. Someting else must be wrong. Coluld it be a bad compressor or an expansion valve? I dont know how to figure out what it is.

Gustav4523 wrote: Sun Jul 05, 2026 3:52 am R12 is not legal in my country so I cant búy it.

Okay...sounds like your car is a candidate for conversion to R-134a, if it's available.

Gustav4523 wrote: Sun Jul 05, 2026 3:52 am I did check pressure in system this morning with engine on. It was 72 F and system pressure around 73-74. That indicates that I have enough refrigerant.

An ambient temperature of 72°F is a bit lower than the ideal temperature for testing the pressures. Test them again at 85°F or higher, then post the results.

That said, your posted pressure range of 73-74 (in PSI, on the high side??) would indicate that the system is nearly empty of refrigerant. Did you check it with a Manifold Gauge Set, or something else? At that ambient temperature, the high-pressure side should be around 175 PSI with a full refrigerant charge.

Gustav4523 wrote: Sun Jul 05, 2026 3:53 am Someting else must be wrong. Coluld it be a bad compressor or an expansion valve? I dont know how to figure out what it is.

Mobile Vehicle Air Conditioning (MVAC) is much more complex than many people realize. With a 58-year-old vehicle, it could be one or more components in the system that might be leaking and/or defective.

I believe you'll best be served by taking the vehicle to a trusted, professional shop that works on MVAC all the time, and let them handle the job. They'll advise you about what is wrong, what it will take to convert the system to R-134a, and of course the cost of repairs.

Gustav4523 wrote: Sun Jul 05, 2026 3:52 am I did check pressure in system this morning with engine on. It was 72 F and system pressure around 73-74. That indicates that I have enough refrigerant.
An ambient temperature of 72°F is a bit lower than the ideal temperature for testing the pressures. Test them again at 85°F or higher, then post the results.

That said, your posted pressure range of 73-74 (in PSI, on the high side??) would indicate that the system is nearly empty of refrigerant. Did you check it with a Manifold Gauge Set, or something else? At that ambient temperature, the high-pressure side should be around 175 PSI with a full refrigerant charge.

Thank you!

I repeat the readings. When outside temp is around 72 F, car is not running and been sitting for at least 8 hours, pressure is around 73-74 psi on both sides.
With car running, low side is around 28-29, and hight side 100-110 psi. According to the service manual, for that temp, high pressure should be 150-220 psi. Low pressure is within specs.

Thanks for clarifying.

Gustav4523 wrote: Sun Jul 05, 2026 12:07 pm I repeat the readings. When outside temp is around 72 F, car is not running and been sitting for at least 8 hours, pressure is around 73-74 psi on both sides.

So the static pressure is 73-74 PSI.

Gustav4523 wrote: Sun Jul 05, 2026 12:07 pm With car running, low side is around 28-29, and hight side 100-110 psi. According to the service manual, for that temp, high pressure should be 150-220 psi. Low pressure is within specs.

If you're testing the pressures at about 1,800 RPM, you are correct that the low side is within specs. However, the high-side pressure is significantly low, as you already know.

Yes, the problem could be a "tired" compressor that's no longer capable of making sufficient pressure, a defective Thermostatic Expansion Valve (TXV), or other problems. But before replacing some very expensive parts with questionable results, first you'll need to have the system charged correctly.

In an earlier post, you explained that your '68 Buick, which originally used R-12, can no longer be recharged with R-12 because it is not available and illegal to use in your country. This means that you'll have to convert the system to R-134a.

However, a conversion is difficult to do and is best left to a professional MVAC shop. Additionally, a reputable shop should also stand behind their work so that if anything goes wrong, you could bring the car back to them under warranty.

Either have a shop do the conversion, or look for another car (1994 or later) that already uses R-134a. Neither alternative is easy nor inexpensive, I know.