a/c question

I've ran into a snag on a 96 tahoe a/c, a year ago the compressor gave up,i replace the compressor, accumulator,orifice tube, expansion valve and condenser,flushed the lines and evaporator coils front and rear,it worked perfect until the other day the compressor locked up,the oil was clean and no metal was found on the orifice screen,but I flushed the whole thing again,and replaced all above parts again,I drained the compressor and refilled it both times with 8 oz's of pag 150 oil,the system was held under 30 inches vacuum according to the gauge for over 2 hours both times problem is when I get about 20 oz's of 134 in the system which isn't enough to keep the compressor from cycling too fast with the engine at 1500-1800 rpm's the high pressure will go to 350-375 psi and the high pressure switch will shut of the compressor, once it starts this the low side want drop below 50 psi because the compressor is cycling too fast,I thought I had gotten a bad orifice tube so I installed another one and still have the same problem,the rear unit is working fine it's gas flow by-passes the accumulator system,the front unit isn't working,the line from the orifice tube to the evaporator is cool and sweating but nothing else on the low side is cool or sweating,as a normal it will sweat all the way to the compressor,what could be restricting the gas flow thru the evaporator,thanks in advance for any imput on this problem

With front and rear air the pag 150 oil capacity is 11 oz. If there is any moisture in the system the 150 oil will tend to gel and block the orifice tube which will give you the symptoms you have. If you think you may have a moisture problem hold a vacuum on the system for a minimum of 4 hours.There are alot of low spots where moisture will accumulate in the dual air system

Is the condenser fan/s running,or the engine fan running,and drawing air thru the condenser? High hi side pressure is usually caused by poor/no air flow thru the condenser,or an over charged system-which you don't seem to have.Mark

forgot to mention the first time it done this I set a fan in front of the condenser no change,it wasn't overcharged as I only had 20-24 oz's of gas in it.

1. Until you OVERCHARGE the system, high-side pressure is largely determined by condensing temperature. (Unless non-condensible gasses are present, which should not be the case since the system has been evacuated.0

2. What is the temperature of the condensed R134A leaving the condenser?

3. Have you checked for condenser for EXTERNALLY clogging... remove the top half of the radiator shroud and see how many dragon flies and grasshoppers and other debris has been relocated there.

You have Bob's attention there is not much more I can add he is the man on AC... Play along and answer his questions no matter what anyone else suggest...

I will add I am thinking a restriction on the high side of some sort. Were is the expansion tube is it located on the outlet of the condenser if so its possible to conect the lines up backerds there :?:

I did a search the expansion tube is mounted on the outlet of the condenser... Both lines have the same fitting :shock: I have seen the lines crossed up before :shock: :shock: I hope that's yer issue...

make sure you do not have a bad fan clutch, should move lots of air. If you run garden hose on condensor, and high side goes down to under 200, replace fan clutch. You should never flush evaporators you will never get the flush out, and i mean never. hope that helps