Automotive Air Conditioning Information Forum

Hi everyone,

I am a young guy, still trying to learn about these systems. I drive a 1979 Lincoln as my daily car, it got me through college and I don't want to get rid of it just yet! I live in Las Vegas so A/C is a must, this summer my old A6 compressor started leaking and slinging oil, and almost every shop I asked wanted $1,000+ to install a new compressor and re-charge. So I got my EPA 609, installed one of the newer S6 compressors, changed the receiver / drier, pulled a good vacuum, and filled it up per spec with 4lbs of R-12. It was blowing cold for about a day, and then some issues started arising. Now, it is blowing 75 degrees on the freeway, and 60-65 degrees at idle. I thought it was odd that it blows hotter when the car is moving faster, usually it's the other way around... If the engine is completely cold in the morning and I start it, it will blow in the 40's, but as soon as I shift to drive and moving it gets hotter up to the 60's.

The low side pressure is reading 50psi at idle, and 35psi at 1500 rpm at 95 degrees ambient temperature. I cannot check the high side yet, as Ford used a 1/8" high-side port from 1977-1980 and I cannot for the life of me find an adapter for it. Finally found one made by Mastercool on eBay so I'm waiting for that to arrive.

Another thing to note, is the temperature control selector on the dash does NOT affect what temperature is coming out of the vents. Before, when you would set it to HOT with A/C on, you would feel a difference. The temperature control selector is cable operated, and the cable is attached to this part:
https://www.ebay.com/itm/1977-1978-1979 ... SwI0tc3ik-

Is it possible that if this part is not working correctly, it is affecting the mixing door and thus affecting cooling performance? Another thing to note is that I have stock cooling on this car (original radiator, flex fan, no electric condenser fan), but I don't believe it is a cooling system issue, my engine is usually at 195-200F (I installed an aftermarket temp gauge as the stock Lincoln only had a temp warning light). I can install an electric condenser fan if anyone believes that will help.

Before I take the car to a mechanic, I wanted to post here and see if anyone had any advice. There are few shops in town that still work with R-12 systems, and the ones that do said that they can recover my refrigerant but that it cannot be re-used because it will be contaminated, so they will have to charge me for new refrigerant. Is this true? If not, I may just buy my own recovery machine if the issue lies in the refrigerant system.

naskobal wrote:There are few shops in town that still work with R-12 systems, and the ones that do said that they can recover my refrigerant but that it cannot be re-used because it will be contaminated, so they will have to charge me for new refrigerant. Is this true?

I'm under the impression that the recovery systems filter the refrigerant (even R-12) and that it can be re-used, and you should only be charged for any R-12 in addition to what your system had. I'm in Phoenix, my local mechanic still does R-12, and 3 years ago added dye and a few oz. of R-12 to my 1988 Mazda truck using his system; I only was charged for the additional R-12, not what my system contained.

Feel the low pressure line at the firewall once it's been running, see if that's real cold, because it is possible that hot outside air or even air from the heater is getting into the flow.


By the way, my 1988 Mazda truck does use that adapter you mentioned for its high side fitting, I have one. Of course GM and Toyota in that era used a slightly different high side adapter !

I believe the 1979 Mark V still had a POA valve on the low side.

The low side should remain steady, and around 30 psi.

That heater valve was a great idea 40 years ago. They are subject to the ravages of age, and poorly maintained cooling systems. Since it is 105f here in Las Vegas right now I would bypass that valve in the engine bay, with a short loop of 5/8 hose at the engine. Remove ALL of the hot water from the cabin while we sort out the rest of it.

You really need to get us some pressure data, both high & low side - at idle, and 1500 engine rpm.

Cusser wrote:
I'm under the impression that the recovery systems filter the refrigerant (even R-12) and that it can be re-used, and you should only be charged for any R-12 in addition to what your system had.

Cusser, I agree, but I am having a hard time finding anyone here in Vegas that will recover and re-use without charging me their rate for new R-12. I am almost considering buying an old Robinair machine myself!

bohica2xo wrote:
That heater valve was a great idea 40 years ago. They are subject to the ravages of age, and poorly maintained cooling systems. Since it is 105f here in Las Vegas right now I would bypass that valve in the engine bay, with a short loop of 5/8 hose at the engine. Remove ALL of the hot water from the cabin while we sort out the rest of it.

Bohica2xo,
You are awesome. I can't believe I didn't even consider this. I completely isolated the heater core / heater valve (looped the inlet and outlet with heater house as you mentioned), and now I am getting significantly lower temps. 25°F on the freeway which I am more than happy with. Looks like the inside of the valve is corroded and allowing coolant to pass through the cabin. Ordered a new one... but I may not even use it since I rarely run the heater here in Vegas.

On the flip side, I finally received that adapter that I needed for the high side (Mastercool part# 90373), and I checked the pressures. Here is what I got:

Outside ambient temp: 100F
Engine temp: 195F

Idle PSI:
Low side: 40PSI
High side: 275PSI

1500 RPM:
Low side: 35PSI
High side: 275PSI

The high side did not really change when I upped the RPM. What do you guys think, do these pressures seem too high? Keep in mind a little bit of refrigerant has been lost each time I disconnect / connect my hoses, so the system may not be fully charged, but I am more than pleased with the cooling performance.

Below is a picture of my pressure reading at idle: