A/C question from the smart FSJ folks

[bjersr]

I have a car with a orifice tube type of A/C system. I replaced the compressor, dryer, and O tube. The book I have siad it should take about 2.5 lbs of freon and the low side should read 25 to 37 psi. I filled it to 35 psi and stoped because I was worry about over charging. I had only put in about 16 to 18 oz of freon. I know this was less than than required but I stoped due to the reading. The pipe going into the evap is cold and the pipe comeing out and going into the dryer is warm to hot. I drove it around for about 15 min and it only blows about 78 degrees out of the vents. Could it be the condensor? I'm going to try to put some more freon in today and see what happens.

[seventynine]

What is the high side pressure? What vehicle is it? Was it converted from R12 to R134?

If it's R134 going in to a R12 system you are supposed to use 85% of the recommended R12 amount.

Dean

[babywag]

Did you evacuate the system?

Was the service valve closed so you're reading the low side system pressure and not the charging pressure?

[Mark G]

Yes, you really need to have a vacuum in the system to make sure the refrigerant is dispersing properly.

[jeepjerry]

Yes, you really need to have a vacuum in the system to make sure the refrigerant is dispersing properly.

Right, r-12 and 134-a dont mix and contamination in the a/c system can cause problems you dont want.

You should have 25-37 psi on the low side while the a/c is running with the clutch engaged. With the a/c off, like while you are charging it up, the high and low side pressures (static pressures) will be the same, probably between 60 and 80 psi, but when the a/c is running, the low side will drop to around 25-30 and the high side will go up to around 150 psi or more.

[bjersr]

Thanks for the response there is no high side port. It's on a 92 volvo 940. I did convert it to 134a. I was able to get about the right amount of freon in it, but the low side was reading about 40 to 45 psi and I know this is high. I know I should have put a vacuum on it, and if you can belive this I have a new vacuum pump to do this with, but it's the classic story in a hurry and didn't want to bother with it. It's blowing about 50 out of the vents. I'm still thinking about taking the freon out and pulling a vacuum and recharging it but I hate to waste the freon.

[jeepjerry]

Its working now so thats all that counts....

I believe a 25* drop or so out of the vents compared to ambient temperature is acceptable. Also, if 134-a is over-charged, it will actually hurt its performance.

[swampedge]

What was blocking the O tube? Your receiver drier will not last long as it's not rated for 134a. I doubt that you make it through summer before having to do it again. I would definitely get a high side service port on it. On a hot humid summer day you can see high side pressures in the 250+ psi. You don't want to see much higher than this with old hoses. Good luck.
Jim

[rocklaurence]

I dont believe it takes 2.5 lbs. My 2.5 ton hose unit only holds 2.5 lbs. Good luck.