Just installed A/C in my F150. Came out of an '87, I have a '94. I replaced the o-rings, and charged it up with 30 oz of 134 and oil. Anyone know if I should go for 20# 30#, 40# on the low side? So far it's cool, but not ice-cold. Also, it is cycled on 100% of the time right now. It cycled on-and-off while I was putting in the R134, but after I got about 20 oz in, it stayed on continually.

 

The pressure on the low side depends on the ambient temperature. I'd put a thermometer in front of the grille and measure it there.

Here's the information from the chart that I have:

Degrees (F) / Low side gauge pressure

65F / 25-35psi
70F / 35-40psi
75F / 35-45psi
80F / 40-50psi
85F / 45-55psi
90F / 45-55psi
95F / 50-55psi
100+F / 50-55psi

Usually what I just do though, is charge until it doesn't cycle going down the highway with the AC on full blast.

Also there's a low pressure cycling switch, that should plug into a port on the accumulator / drier. This has an adjustment screw between the two prongs. I believe for a retrofitted R12 system you want to turn that out (counterclockwise) approximately one turn. I'd do that first, then charge.

 

ah, thanks! I charged it to about 25# at about 70F last night. It wouldn't cycle off very often on full blast sitting in the driveway with the accellorator pressed a little bit. I will turn out that screw a little bit and give it a try before adding more r134

 

Careful as you tweak that low pressure cutout switch. The reason is because, at the typical suction side pressure of around 35psi, the evap core temp is roughly the same. You drop that suction side pressure down (and thus the temp) and hold it there too long and you will turn the evaporator into a block of ice. The odds of this happening will increase on humid days as well as cooler days.

 

ok, well, in the 5 minutes I had it running, the accumulator was frosting up pretty good. Maybe I'll leave it there. I just wonder why it was not cycling on and off, just seems to stay on 90% of the time. I'll take it for a test drive tonight and see if it cycles on-and-off.

 

If the accumulator is frosting up it is still low on refrigerant. It should be cold and have condensation building up on it but not frosted. If it frosts up, your evaporator will freeze and all the condensate that builds up and freezes will stop the air flow.

 

ah, thanks! I put one more can in last night. When it is on (compressor clutch engaged) it's reading about 30# now. Maybe still more? Compressor still running 100% of the time, even when I drove down the road last night. That is at 65 degrees outside. Thanks so much everyone!!

 

I hope you pulled a good vacuum on it before you charged it. My 88 holds 52 ounces of refrigeran (3.25 lbs). That is from the shop manual.

 

what will you loose if you don't pull a vacuum, just volume of refrigerant? I have 50oz in it right now.

 

If you don't pull a vacuum you run the risk of air and moisture in the system which besides displacing freon and reducing overall cooling will react with the freon and eventually kill the compressor.

John

 

It is not a good idea to put refrigerant into an empty system without pulling a vacuum because;
1. There will be air in the system that will not condense and it will cause your compressor discharge pressure to be very high.
2. The air in the system will cause oxidents and acids in the system that will corrode internal parts of the compressor.
3. Air in the system has moisture in it and that moisture will condense into waterin the system and the water will emulsify the oil in the compressor.

 

ew boy, thanks!