hi this is my first time using this web site and I'm about to pull my freaking hair out. i have a 01 f150 4.2L and a while ago the ac compressor clutch broke. i didn't catch it in time and the stress it caused on the belt broke the power steering pump pulley. so i replaced the steering pump and pulley and the compressor the accumulator/dryer and the office tube put the 134a back in and everything worked fine. three months later ac stopped working. i figured the condenser was bad so i replaced it. charged it up still no cold ac. so i thought maybe the manifold that goes on the compressor was clogged so i replaced it. while i did that i said to myself well i should tear out the dash and replace the evap as well. so just about everything has been replaced on the ac system. aside from the cycle switch and the high side switch witch from my test both seem to be working. now here is the thing. the tube witch holds the office gets ice cold then goes to the evap but the suction line coming from the evap doesn't get cold and the ac blows warm air. this very problem is what convinced me that the evap was clogged and needed to be changed witch is why i undertook the task of tearing the dash out. in all it took 14 hours to do the whole job. now for the pressures that i get from the ac manifold low side goes 40 down to 20 ..... this is normal. high side is a little high. i charge it to 125 still no cold air. so i dump a little more 134 in. at 90 degrees high side pressure should be around 200ish i get it there still no cold air. someone please help me for i have just about replaced everything i can think of.

 

heres an update just to include this i do have a 2.5 cfm vacuum pump and experience working with ac units. just not car ac

 

dropping down to 20 psi is a little low. I normally like to stay at 30- 35 psi. Top end at 200 or a little higher is o.k. I don't think you have anything plugged or your pressures would go high on the high side.. EIther your a little low on gas, or you have some air in system ???

 

Isn't the cycle switch responsible for the low side pressures. The compressor turns off at 40 and turns back on when the pressure hits 20? As for the air in the system this could be possible because I used the 12oz cans and didn't purge the hose when changing cans.

 

Sounds undercharged to me.

Did you 1) vacuum the system and 2) WEIGH in the refrigerant to the specification (or just guess)?

 

Yes I put vacuum for 1hr and added 32 pounds. What I'm not understanding is the pipe coming from condenser then through orfice that pipe is cold but the pipe is cold then it goes to evaporator but the pipe coming from the evaporator isn't cold. How can this be the evaporator is brand new why would the pipe feeding the evaporator be ice cold but the pipe coming from be warm?

 

Did you install the o-tube backwards?

 

Normally, that means it's undercharged. The refrigerant is evaporating and then superheating in the evap because it isn't flooded. How did you weigh in the refrigerant? 32 *ounces* is not quite three 12-oz cans. How do you know you had 4 oz left in the last can?

At 90 degrees ambient, I would expect the high side to be closer to 230 unless you have an external fan blowing extra air across the condensor. Also, the time for which you pull vacuum isn't as important as it holding a vacuum. How much of a vacuum did you pull? I am doubtful you have any major leaks, but it's always possible, and if you just turned off the vacuum pump and started charging, you wouldn't know. While using a micron gauge on a vehicle is really overkill, they are very good for determining if you are leaking.

You have it backward. When the low-side pressure drops to 20 (or thereabouts), it opens, turning off the compressor. After the pressure rises above 40 (or thereabouts), it closes again.