A/C charging questions

[84toy]

Tried to find this by search but no luck. Can somebody post or direct me to a chart for R12 pressures@temp for an 84? Need low, high at what RPM of engine for proper charge. If everything is working properly on a stock setup, what temperature at the vent should I expect?

Thanks

[Por_sha911]

I can't help too much on the pressures but I know that a fully charged system is suppose to have 3 lbs of R12 (less if you use other coolants). Vent temp seems to vary from one car to the next. I suspect it may be affected by outside temp, color of car, accuracy of thermometer or method used. I just recently fixed my AC. It was about 85 outside today and I got a vent temp of 48 (after driving a few minutes at speed).

[84toy]

Thanks. The system was operational but of course not putting out much cool air. The PO had the compressor belt off so I don't know how much R12 was in the system already.

I started charging the system but got nervous as the pressures started to climb. The ball in the sight glass is still not floating but the air temp at the vents is very cool. The pressure was about 25\275 with todays air temp at 88. Sitting there idling in the garage for a long time does not help the pressures I'm sure. I set the engine at 1200 RPM while I tested and charged

Should I add more freon and get the ball floating and should the pressure be this high? Should I let the engine cool down and recheck the pressures?

[SC-targa]

I've always just charged mine until the ball floated in the sight glass.

When you hooked up the gauges, how did you close the deck lid? You risk blowing the whole system with high pressure with an open lid. The AC uses the engine cooling fan as the primary condensor fan.

My stock AC runs center vent temps of 44 degrees at 70 MPH on a mostly sunny, 90 degree Texas day. With the small vents in my SC dash, that's just about good enough, but certainly not like a real car's AC.

Regards,

Jerry Kroeger

[Por_sha911]

Several thoughts:
-Always lower the decklid like Jerry said.
-You really should evacuate your system before dumping more coolant on top ( you can place too much pressure in there by "just keep adding a can till it gets cold"
-If your system has been exposed to atmosphere (zero pressure in the system) you will need to replace that receiver/drier (the thing with the glass window) and you more than likely have a leak that will need to be fixed or you're just pumping coolant in one end and out the other...

[scottb]

I did a complete reworking of the a/c system in my 84 last year. If I recall correctly, I got the following information from Jim Sims here on the board. Here's the resident expert on all things a/c.

I hope this helps.

Typical high side pressures (without adjustment for altitude):

For R-12
80 F ambient 170 to 210 psi
85 F ambient 180 to 220 psi
90 F ambient 190 to 230 psi
95 F ambient 205 to 250 psi
100 F ambient 220 to 270 psi

For R-134a
70 to 80 F ambient 115 to 200 psi
80 to 90 F ambient 140 to 235 psi
90 to 100 F ambient 165 to 270 psi
100 to 110 F ambient 210 to 310 psi

Typical low side pressures (not adjusted for altitude):

For R-12
32 F Evaporator temp 30 psi
36 F Evaporator temp 35 psi
42 F Evaporator temp 40 psi
48 F Evaporator temp 45 psi
53 F Evaporator temp 50 psi

For 134a
33-50 F Evaporator temp 16 to 29 psi
33-60 F Evaporator temp 19 to 39 psi
40-65 F Evaporator temp 25 to 43 psi
48-65 F Evaporator temp 37 to 51 psi

[84toy]

Good info, it sounds like I am close. My high side is a little high and my low is a little low but getting air of about 41 deg at the vent with my top off. I did have my decklid closed over the top of my hoses. Do you know what RPM to run the engine while taking these readings?

Thanks

[scottb]

When we did mine, I think the RPMs were at about 2000.

41 degrees at the vents is pretty good for a stock system. I get mid-30s, but I have an auxilary condenser/fan assembly, and a ProCooler.

[jdowty3]

To resolve the problem with closing the decklid, place a box fan against the raised decklid (bumpered by towels) to blow air through the condenser.