I have a '94 f150 with a 4.9. I converted it to a/c and originally it did not have a/c. I put a new drier on and orifice tube (variable type). I did not put a vacuum on the system and I charged it but I only get 53/54 degrees at the vents. I charged another truck of mine w/o vacuuming the system and it blew really cold (not sure of the temp but it was enough to have condensation running off the back window). would the ambient temp. outside have effect on a/c capability? when I checked vent temp. it was only like 65 degrees out and a friends 97 f150 blew 36 degrees from the vents. if my compressor is bad or going bad would it not be strong enough to make the freon as cold? the system is charged at about 50psi on the low side when running. would moisture in the system effect this and/or what kind of effect would it have on an a/c system? I have a few questions and would like to understand a/c systems a little better, any help would be greatly appreciated.

 

Without pulling a vacuum there are any number of possibilities, moisture in the system, air and moisture, etc. 55 on the suction side seems high what are you reading on the high side and at what RPM are you reading these pressures? Moisture and air displace freon for one thing so you are reducing the freon capacity of the system. Also, since you are transforming freon from liquid to gas and back, air/moisture has different boiling properties than freon which also will cause problems. My recommendation is that you get yourself a good vacuum pump. Remove the freon and pull a vacuum for at least an hour possibly longer to dry out the system and remove any air. Recharge the system and you should be good to go. Let us know how it goes.

John

 

Yeah, I was thinking the same. I just bought a set of a/c gauges and I got a vacuum pump from work so I plan to do it the right way. I have a reman. compressor I am going to put on now since I am evacuating the system. I had it the whole time but I put a used one from another truck on because it worked while in that truck but now it is making some noise. Freon is too expensive to be emptying and refilling. A year ago is was no thing.Now is a different story. I just put a new drier and orifice tube in and since I am changing compressor to a new one get I get by with what I have now just because it has only been on a few days? Do I need to vacuum it for an hour or since I have gauges just vacuum it to 30 inches? Thanks for your help. I will let you know the outcome of this.

 

Moisture boils under a vacuum so the longer you pull the vacuum the greater the chance of vaporizing all of the moisture in the system. By just getting the system to 30 inches will vaporize some of the moisture but again the longer you pull the vaccum the more chance for getting all of it. The biggest risk you run is the moisture in the system soaking the dessicant bag in the drier and possibly killing its effectiveness. Also, over time moisture mixing with the refrigerant oil will form acids that will over time destroy the compressor, seal, etc. In your case it shouldn't be a problem since you haven't operated the system for very long. Pulling the vacuum will help to dry the dessicant but not sure at what point it is useless because of excessive moisture. I have never had a probelm with the drier after opening it up to atmosphere if I pulled a vacuum right away. The sooner you can discharge and vacuum the better unless you are going to go ahead and put in another accumulator/drier. Depending on the cost for the drier it might be a good move, since as you say freon isn't cheap and you don't want to have to tear into it again.

John