How Much R134A is Enough ?

[CrewCabDiesel]

I have been trying to get my AC system to cool down to reasonable levels. How many CANs of R134A is the system suppose to hold to work correctly? My high pressures are running about 275psi and it doesn't cool for s**t . Best I can do for Vent temps is 60-55 degrees.

 

[bvanetten]

Was your system originally designed for r12? If so good luck. Seriously though, for a r12 conversion to work close to factory you need to change more than the oil and seals. Go to a parrallel flow condenser as big as you can get and put in a "VOV" variable oriface valve. Or better yet save yourself money and headache and put r12 back in. It's 34. 50 at autozone and if you don't have a dual system it shouldn't cost you much over 100 bucks. 134a just plain sucks. The higher head pressures you will run with it will wear out parts faster and get this. This really chaps my hide. For r12 and 134a to turn caustic (because of moisture content in the system) you need to have over around 50 parts per million of moisture in the system. At this level and above the refrigerent will react with the water and produce an acid that will eat your compressor for lunch. THE OIL THAT IS USED IN 134A SYSTEMS HAS ABOUT 800 PPM OF MOISTURE! Talk about engineered part failures! Go to http://aitcondition.com and search the archives. Lots of good info and knowledgeable people.

 

[RDusch]

Crewcabdiesel



What pressure are you running on the low side??



With your engine running at 16-1800 rpm your low side pressure should be 29-30 psi, that equates to 33-35 degf of saturated suction pressure, and with that and a clean evaporator you should get 45-50 air from your vents,



High side pressures can get over 300 easy with the truck not moving and a high ambient temp.



pressure chart below might help.



Rick D.



click here for temp pressure chart



(SIDE NOTE Bvanetten is definetly right above, the pressures and temps i've given are for a system with the proper parts, conversion are sometimes lacking the efficiency needed to produce the wanted outcome.



if you are running a conversion and 12 is not a viable option check out Auto Frost Site

 

[Racer Brown]

Low side pressures

RDusch is right on with the Low side temp thing. I still have my old 83 Chevy (cough) that I converted to 134 about 7 years ago. When I set that one up, I set the low side pressure at a point where it was just above freezing in the evaporator. That pressure will vary some with ambiant temp variations but if you set the low side pressure where he says, that may do it. If you happen to have the evaporator freeze up, just hook up to it and add a pound or two to the system to cure that. Remember, the temperature in the evaporator is controled by the low side pressure in the system. Your compound gauge set has a temperature crossover listed below the pressure on the dial so you can get an idea of what's going on in there when it's running. Rule of thumb is that the exit air temperature is usually around 20 degrees higher than the evaporator's actual temperature. Hang in there! These systems can be made to work.



Also, if you do a search back in the archives here, you'll find out there is a R-12 substitute available that is not harmfull to the ozone layer. I forget the name of the stuff but several of the ppl in this forum have used it with good results. Have a look and see if you can find out what it is.



Hope this has shead some light on the subject. See Ya! Racer

 

[bvanetten]

oops

I fat fingered the link. http://www.aircondition.com



autofrost is good stuff. The inventor, George Goble is good people. He posts to the above site often.

 

[Scot]

Also make sure you have the correct amount of oil in the system. Overcharge will cause trouble.

 

[jsimpson]

80 -90% of an R12 fill. DON'T try to eliminate the bubbles in the sight glass. R134 in my 89 freezes me out of the cab in South Florida. DON'T use any "substitutes". You won't find a reputable AC shop that will work on your system if you do.