I just did a A/C sercice on my 1996 f350 7.5l. It had a slight leak I repaired, installed a new orifice tube P/N 38635 and a new receiver drier. I added 4oz oil to compensate for the 3oz I drained out of the accumulator. I charged with r134 until the high pressure was 275 and that put my low pressure about 50-55. It isn't that cold and the compressor never cycles. I only get about 60* out of it and before It would set in the 50* range. I tried sucking some Freon out of the thing to get the high side at about 250 and that put the low side in the 50 range. The oil was iso46 pag. I only bought 8oz and I have some left over, I measured in a ratio right, and not sure what is going on. I have done lots of ac work, conversions, and am comfortable with my competence level, but I might need to change something, seeing as what I have now is not satisfactory to me. Any input on what I might have missed?

 

Exactly how many ounces R134a did you put in?

 

did you pull a vacuum in the system before you charged it.

 

I have no scale. I have never used one and generally have good luck reading the pressures. I pulled a vacuum, then charged it to 0 with Freon, then pulled the vacuum again, then charged it. I personally feel that the low pressure side is slightly high, I am not sure of this, but it is something I will look into. Maybe my new orifice tube didn't seat all the way into the line, or maybe the o rings on it are bypassing, I am not sure but it doesn't seem right.

 

your 96 should only take 2.2 lbs, or 3 cans of refrigerant.
my guess is that it is way overcharged.

 

I agree, sounds like it is overcharged. Did you use a thermometer to check if temp was changing/dropping when you were adding?

 

tjc nailed it................

 

75* ambient temp needs 25-30 psi low side. 85* ambient temp needs 30-35 psi low side. I would say you are either over charged, or your clutch fan isn't pulling enough air thru the condenser and the high temp up there is killing your cooling ability and /or giving you falsely high readings. Turn the garden hose on the condenser and see what happens.

 

Low side at 50psi! That is over charged for sure! My AC low side runs 20 to 35 psi depending on how hot it is out side. I use just a low side gauge(hand gernade gauge) and not sure what the high side is.

It takes less R134 in the system than R12 to function properly.

 

I guess I must have an underlying problem. Thanks for the help. I have had to add just a little bit every year about this time to get the air cool. When I am running around town the air blows about 45-50, when it has gone above that, Time to hook up the tank and give it a little shot. The pressures always seemed over 40 on the low side, and right in that 250+ range on the high side. For 3 years, it would start blowing warmer (60* air) and after adding a little bit of Freon, back in the saddle. When I say a little bit, that is exactly it. like maybe 1/2 pound, or less. I never became dependent on the weight because of multiple reasons, on ag and construction equipment, there wasn't always a capacity available. Furthermore, on commercial trucks, one might have had a sleeper, then converted to a daycab, but the lines might still be under there just capped or plugged. hard to get a accurate reading with that in mind. Also, On JD equipment, the compressors are superceded to a different one, as well as the condensers and evaporators and the lines and the driers. Capacities aren't the same as factory anymore, so a weight is not going to be correct anyway. I like the scale idea in most automotive apps, but not feasible for the type of work I am involved in.
Like a JD corn chopper from Germany, somehow ended up here specs are listed as "not available in the US" Fly by the seat of your pants. thanks for the reply, I am going to open it up and do a drier with a ford one, the orielly doesn't even fit right, and a new orifice tube, again, and try that. See if he pressures work out better this time. If not, then we will do a new compressor, flush, clean condenser, and go from there.

As far as the condenser, The input side is so hot I can't even hold my hand to it, and on the exhaust side, it is warm, not even uncomfortably hot, just warm. That is usually my indication that the condenser is working, but help in requested none the less.

 

Condenser temp sounds about right, but try the water hose trick with the gauges hooked up and see what you get. If the pressure drops considerably, you may want to check the fan. Only a little change, no problems-all systems normal. I'm a "fly by Levi's" kind of mechanic,too. Juice it up 'till it works right and call it good is my motto.

 

I fixed it. I evacuated it, put an accumulator on from carquest, it actually fit, and I installed a 38639 orifice tube, the slightly smaller orifice, and now 38* air at idle, on low or medium, 35* air on max ac setting (recirc) and 250 psi high port, 20-40 low port. I cleaned the condenser, and part of my problem was that my gauges always had pressure retained in them, and when I let them zero out, the settings were not on zero! In fact the high port sat at about 15 psi, the low port sat at about 6 psi, so I zeroed them, and that made a huge difference. The pressures are not all out of wack now.

As far as the smaller orifice tube, that was a very productive mod for low rpm low speed operation. It cools better at idle because the pump can hold the higher pressure as well as the low pressure isn't climbing up, just enough more restriction for our southwest hot and slow driving. At 90* out, I now have 40* air, at idle, and high pressure side doesn't spike over 300, usually 200-250.

Moral of the story, keep the condenser clean, use good parts, and make sure your equipment isn't too far out of calibration. I don't recommend this mod, and it should not be attempted unless you know your system, and how AC works. This will not always help and in cooler climates, I feel that this mod will hurt the operation by not letting the Freon flow like it was designed to, but mine is exceptional, when it is hot, it is hot. This could have been easily remedied before posting if I had hooked my old gauges up at the first sign of trouble because the different readings are a dead give away. After using both sets of gauges I figured out that the problem initially was a plugged condenser, and possibly over charge, but the high port was really about 15 psi lower than my original postings, and the low port was about a long ways out as well. Actual readings are not what was posted. Sorry for the confusion and thanks for the help.