2002 Ford E-450 Bus - A/C Issues FIXED!!!!!!!!!

[erlesauto]

I've got an 02 E-450 diesel bus with a sidemount condenser unit and rear carrier unit.

Replace siezed compressor, flushed out system, replaced accumulator and orifice tube, replaced inline filter on rear unit. My problem is when you accelerate to about 1500-1700 rpm the high pressure relief valve on hs hose opens at 250psi. I disabled the condenser cooling fans to see what the pressure would rise to and at 450 the high pressure switch cut off the compressor like it should, the relief valve did not pop.

So why at 250 at cruise speed but why not at up to 450 at idle?

[allenjackson]

DID YOU TRY REPLACEING THE POP OFF. AND DONT RECOM. RAISING THE PRESSOR TO 450 IS NOT A GOOD THING

[erlesauto]

Actually I did and it made no difference

[allenjackson]

YA I AM NOT SURE IF I HAD IT HERE MAYBE I CAN HELP.

[protraxrptr17]

Pull the orifice tube out again an look for trash.

[erlesauto]

Clean as a whistle

[steven kiser]

ok, all the fans are working, what's the running temperature of the bus when the pressure valve pops? i've seen situations like this where the radiator has a restricter on it to lower the air flow for higher temp in winter. are the condenser cooling fans restricted? the blow off valve will open when there is an abnormal build up on the high side. when you matt it does the pressure slam on the high side while almost reaching a suction or 0 level on the low? if so there is a restriction. see if this system is set up to loop out the rear. if so do it and see if the system works fine. if yes there must be a restriction in that part of the system. too much oil will cause this, as well as a collapsed line. i've found crushed lines from improper lifting. on some of these there s are shut off valves like i spoke of, make sure the main line ones are open and the loop is closed. if the compressor imploded it usually leaves a debris trail. for the most part i find debris in the condenser. if this bus has sat with the a/c system trashed from last year you'll never get the debris out. it's sat long enough to become solidified. pull the lines off the condenser and see how it flows. there should be very little restriction while blowing air through it once the oil is removed. if there is replace it. i use an air nipple with a restricter on it to control the volume not the pressure. my air hoses are 1/2" and i open the valve 1/4 and if the volume of the air flows without any back pressure after 10 seconds then i accept the condenser as good. a plugged evaporator will give you a much quicker pressure drop on the low side. test the evaporator just like the condenser. these double systems are a pain. there should be multiple ports in this system and i've had situations where i needed two gauges to isolate and repair the system. there should be a set of ports near the side mount condenser. if those gauges react quicker than the front lean towards the rear system being the issue. i sad lean, not accept that as fact. i have a friend that is a head tech at a bus garage. i can e/mail him and see what he thinks. i just thought of something, there should be two expansion valves in this system. are they both "clean as whistles"?

[erlesauto]

Condenser fans are working, units are not seperable, rear has ex valve front has orifice. Under acceleratoin high side will reach 250 low side 45 when valve pops. service port is 3ft from pop off. No shut offs in line .

[steven kiser]

there must be a restriction somewhere. i suggest doing a part by part takedown and test.

[liljoe]

It almost sounds like the compressor has something in it restricting the flow inside the compressor between the pop off valve and the high side outlet, I have never seen that, but that is the only way I can se for the valve to blow at 250 psi when it is capable of holding 450 psi with the condensor blocked off. Sounds like an unlikely situation, but might be worth taking a look at......

[protraxrptr17]

Just had an idea, are you sure you dont have too much refrigerant in it or too much oil? Sounds like the compressor is trying to compress liquid refrigerant, if so it wouldnt matter what the pressure was.

[a&mauto]

The temp gun is your friend. If it has high pressure in one place and not another, like if you had blockage, you will also have high temp. Hold the throttle open to about 2000 and follow the line with your temp gun. If you find a temp break, there is your restriction. Otherwise, like mentioned before, you may have an oil overcharge. But, then your pressure would read high on the gauge too. Grab a temp gun and go from there.

[a&mauto]

Also, follow the serpentine coil of the condenser. Look for a temp break.

[1stephen2]

replace the relief valve.!! use only OEM products, once you use aftermarket(china), you're sure to be lost. The reason for it is that china goes by what may work and most times will. but when it comes to pressure and electrical, That is their weak point. OEM products may be more expensive but you have to sell it to them.especially with ford and chrysler. If the PCM does not read the specific set point for the component it will not work when it is supposed to. We find this alot in our shop. once we use OEM by VIN problems are usually solved.

[steven kiser]

It almost sounds like the compressor has something in it restricting the flow inside the compressor between the pop off valve and the high side outlet, I have never seen that, but that is the only way I can se for the valve to blow at 250 psi when it is capable of holding 450 psi with the condensor blocked off. Sounds like an unlikely situation, but might be worth taking a look at......

great point. what is between the compressor and high port. the problem lies there. 250 is way to low so if the gauge is reading 250 there must be a restriction before that. watch pressure when you accelerate. if it drops slightly on the high side after a few seconds (wouldn't be immediate with this size system) there may well be a restriction before the port. going way, way, out on a limb here, is there shut off valves in the system? i've run across add on systems that have shut offs in them for service purposes. what, if anything was done to this system prior to coming to your shop. my thinking is a restriction between compressor and port. the more i look at it the stronger i agree. if you look at a basic generic a/c system with add on's it keeps coming back to that. there has to be some restriction. there is really no other way i can think of that would give you these symptoms. it could be a crimp in a line that someone pried against. i had a truck in the shop with pressure issues, not as extreme as yours but after working my way through the system i found that when a body shop replaced the condenser a piece of packing material had gotten inside one of the lines.

[erlesauto]

Removed blow off valve and installed gauge in its place, recharged system, revved up engine but before I could see the reading the high side hose blew out right between valve and service port. Replaced hose and it is ok.


Thanks for alll the input

[steven kiser]

that must have woke ya up. don't ya just love the smell of vaporized pag or ester oil. glad it's up and running. was the nylon insert collapsed?