A/C High Pressure Switch

Does it work as it should with A/C off...does it go off or is it on all the time?? Is it just going on and off all at odd times?

Something to check. See how much psi it takes to release the clutch. It takes air to release. If you by chance have a small leak in one of the orings in the clutch it will come one at odd times if it looses its psi. You may very well be getting air to it to release it. But if you have even the smallest slit in one of those you may very well see what you are seeing. We have rebuilt a few in our fleet lately and saw that. But it was so bad it would not go off. Could be bleeding off and engaging. Its designed as a safety so if you loose air to it you do not loose cooling. Just a thought. Your A/C equip may be working right. If you do go into the clutch...which isn't a hard job...you can do it in a half a day. Takes longer to get to it. Get the oring and bearing kit. Do the bearing while you are in there.

 

If there was a compressor failure it is entirely posible that one of the expansion valves is stuck closed from debris from not being properly flushed out or maybe the a/c oil was mixed ( pag and ester oil are not compatible and can form a sludge in the system making components fail)old style york compressors take ester oil while the new style sanden use pag.

it could be quickly verified by having an a/c guage set installed in the system and verify the pressures. Or by bypassing the binary switch with a jumper..

hope this helps

 

I had been told a fan clutch air l eak could be the culprit and that it won't leak when the engine is shut off making it difficult to check without tearing into it. The fan will not ever go off once it comes on even with the a/c turned off.

 

I'm positive the correct oil was put in the compressor I watched them charge it. Now some debris still in the lines, is possible.

 

That is wrong...you can check it. Bleed off all your air from your system. Unhook the airline going to the clutch. Build an adaptor so you can hook up to the fitting from an air hose. Use a regulated air supply. Make sure you are able to hear it...ie. away from the compressor. either have someone do it and you listen and watch or vice versa. Then start easing up the regulated psi and watch what the clutch does. At what psi does it open. Record this psi. The ones that we have rebuilt do not take alot of psi to open. If I remember right from testing...after rebuilt they take around 35-40psi...but don't quote me on that. We have had a couple that took 90-110psi to open. They'll open but you'll hear them leaking. They do not get that much air from the line. Also once you find that spot they will open. Take the psi cut the psi from it and see if it will leak down over a little time. It should hold for a good while. This is how we have tested them.

 

If I remember a rebuild kit is 80 or so but the bearings will cost a bit more...if it is leaking be sure to replace the bearings also. They'll come in a kit. You can get a bunch of different rebuild kits for them.

 

it also depends on what kind of fan hub you have.. around 2000 i believe is when the new style horton hub started to be installed.. New style is "air to release" ( if its leaking it wont disenguage properly) like Scrapper said just put shop air to it and use soap to find any leakage.

However old style horton uses "air to apply" so this shouldnt be an issue if you have this kind of hub.

 

Thats right...all our trucks use the newer Horton hubs.

 

You know something. I do have (and have had this for some time now) an air leak that only happens when the engine is running. It is not bad enough to put the truck out of service but it will leak down when sitting there idling. I can let it build up to 120psi, shut the truck off for a week, then go fire it up and it will still have 120psi in it... ...but once the motor is running she starts slowly leaking down. Could this be tell-tale on the fan clutch leaking? I dunno. But I'm thinking the bearings have probably got some miles on them (truck has 1.07 million miles, I put 320K of those on it) and I have never put any in it. So no more than they are and no bigger than the job is I'm going to put new ones in and get an o-ring kit to fix the air leak while I'm at it. I still feel like I'm tossing parts at this ongoing problem lol, but what the heck, just might fix it this time.

 

Can you not unhook the clutch line and put some air to it and listen for a leak?? Have you tried that? It will be about 150 if my memory serves me right to get the seal kit and bearings. The hardest part of the job is getting to it and getting it out. Its heavy. BE VERY CAREFUL when getting it out due to how close you are to the radiator. An extra set of hands is good. You can undo to supports that angle up to support the radiator. Wont give you much but will give you some. We had to go out on the driver side and it was a VERY tight squeeze. This was on the last T600 I did. It would not go out the passenger side or the top.

Also when rebuilding. Make sure when you use the pry bar to get the nut off the clutch that you put tape on the bar and or the studs coming out of the housing. They are easily bummed up. Also pay very close attention to the large gasket that seals the internals of the clutch. It will be folded up in the bag. It has a certain way it goes in. The gasket is wider on one side than the other. Horton has really good instructions with good illustrations. But those are a few things we have learned when working on them.

It will take ALOT of pressure to get the clutch loose. You do have to use a vice. We have normally had to use a cheater and breakover but finally get them apart. Not trying to scare you from it...but you'll think you are going to break something. And normally I think I did but its just the nut breaking loose. lol. Let me know if you have any questions about it. Will be out of pocket until Monday. I'm an agriculture teacher (FFA) and taking kids to the Fort Worth Livestock Show tonight.