I need some air conditioning help

[idacal]

On my 06 dodge diesel this is the third summer I have owned it and its the third time the ac is out, last two times I took it to two different shops, 900.00 once, 1200.00 the second time compressor once, compressor and orifice the second time and still went out in a year . Im not real impressed with the quality of work I can get done locally. My dad has charging and recovery unit that he picked up somewhere. we recharged it because the gas was low but after doing that the pressure was running up around 400 PSI. We shut it down and drained most of the gas out so I dont ruin the pump. Im trying to figure out what parts I need to change, and if there is any tricks that my local mecanics dont know to get this thing to work reliably. thanks for any advice

[rlitman]

That high a pressure could indicate a clogged orifice, or an overcharged system.
Was your accumulator/dryer changed during the last two services (it must be changed any time the compressor is replaced, and should be changed whenever you have the system open to the air)?
Was your system flushed after the compressor failed?

A failed compressor can leave the plumbing filled with crap that will clog the orifice, and kill the compressor. Sounds like it was never properly cleaned from the start.

[Oldiron2]

Is there any chance that the system got some other refrigerant, like R-12, in it too? The pressure of a mix of R-12 and R-134 is well above the pressure of either alone. I agree w/ rlitman about all he said, too; that's most likely.

I assume you also know "they say" the AC system should be used during the winter to maintain the seals; most systems use AC to dry the air when in the Defrost mode, so that is easy to do with them.
BTW, do you have a good leak checker? The flame type is fairly sensitive, and the modern electronic types are even better. I've used mine, by adding a little chloroform and then pressurizing, to test other closed systems for leaks.

Also, does the recovery system have a good vacuum pump as part of it? Removal of moisture from a system requires "sucking it down" for a reasonable time with a high vacuum because water molecules have an attraction to the inside surfaces. Even if you replace the dryer (which is in the accumulator), enough moisture elsewhere can overload the new dryer, if this isn't done. Same problem (moisture) might occur with the recovery system so it needs to be checked thoroughly too.

[rlitman]

Originally Posted by Oldiron2

I've used mine, by adding a little chloroform and then pressurizing, to test other closed systems for leaks.

Thanks! I've got to remember that one. Now its not a unitasker any more.

With high pressure, a leak might not be the first thing to check for, but it is possible for the system to draw in moisture, through a leak on the vacuum side.
Absolutely, if refrigerants got mixed, the pressures will be way out of line too. Good point.

The problem I see here, is that your system is failing so frequently. A proper vacuum purging before refilling is critical, and even with a good pump can take up to an hour to remove a sufficient amount of moisture, BUT no amount of vacuum will remove the crap that gets left behind when a compressor fails. Its that crud that likely clogged your orifice and killed your second compressor, and unless you can get it removed, will kill again.

There are chemical flushes that can be used to clean out the pipes and condenser, and an inline filter can be installed on the liquid side to catch this stuff before it destroys the system again, but if it were my car, I'd replace the condenser and all the o-rings along with the orifice, flushing, filter and receiver/dryer.

[Benjamin.S]

Clogged fins in the condensor will cause high head pressure blow it and the radiator out with compressed air.....

[DougAustinTX]

Originally Posted by rlitman

That high a pressure could indicate a clogged orifice, or an overcharged system.
Was your accumulator/dryer changed during the last two services (it must be changed any time the compressor is replaced, and should be changed whenever you have the system open to the air)?
Was your system flushed after the compressor failed?

A failed compressor can leave the plumbing filled with crap that will clog the orifice, and kill the compressor. Sounds like it was never properly cleaned from the start.

If the orifice or the expansion valve is clogged, you will get extremely high pressures on the High side and you should have a really low reading on the Low side... something approaching zero. If it was simply overcharged with refrigerant, both sides will show high pressures when operating. High side shouldn't be much over about 200 to 230 on the high side with a fan blowing on the condenser and the engine running at 1200 rpm. Low side should be in the 40 psi range ( which roughly equals the air temp coming from the vents).

The guys are correct that the system has to be completely flushed out if it ever had trash circulating from a blown compressor etc. The orifice has to be removed and thoroughly cleaned too. The dessicant pack in the receiver/dryer needs to be correct for the refrigerant and oil that you are using. Some dryers are not compatible with PAG oil and can release dessicant into the system.

Pure propane is an excellent refrigerant that is compatible with all oils, doesn't need to be vacuumed to prevent acid formation, and is easier to compress and more efficient than the R12, R134 etc mixtures...and will not harm the environment if released into the air... but it is supposedly illegal to use it because it is not "approved"... but tell that to the farmers and ranchers who have used it for decades in their air conditioning and freezer systems.