Intermittant AC

[webbz47]

My BJ70's AC has just gone intermittant, most of the time I switch it on and nothing happens but then sometimes all of a sudden it starts blowing cold. When it starts working I hear a screeching noise then the noise goes away. Does this sound familiar to anyone?

 

[Gun Runner 5]

Compressor clutch?

 

[stayalert]

gas leak such that amount in the system is at or near the amount where the pressure switch shuts down operation of the compressor?

 

[webbz47]

When I switch the AC on most of the time nothing happens, there is no current draw, it's like the switch doesn't work. When it does activate I hear the screeching sound (belts moving ...pulleys not?) and the AC behaves as normal. Do I need to remove the unit to check the clutch?

 

[Gun Runner 5]

Someone with a higher paygrade will have to answer that however based on the symptoms you described I would be surprised if it were not the compressor clutch
that is causing your issue.

 

[Radd Cruisers]

The screeching sound is almost always caused by a compressor that is cooked - where "cooked" is defined as: shedding parts into the system, and is seizing and needs to be replaced.

The other problem is that if the compressor has died, it's likely shed bits of metal into the system and that is going to need to be cleaned out. Usually this is done by using a solvent to flush out the system, thereby removing all of the lubricating oil which will have have to be replaced.

And to further complicate things, if you're going from an R12 system and 'upgrading' it to R134a, then you're going to have to change the valves on the compressor (or fit conversion valves) as well as replace the seals (rubber o-rings) that go between the various connections. (NB: that R12 is a better refrigerant but is very ozone unfriendly and is either banned or strictly controlled in most jurisdictions. Venting R12 into the atmosphere is punishable by quite severe fines if you're caught doing it. - plus it's quite valuable and you don't want to vent it in any case).

And, even a further note, that there are different lubricants used with different refrigerants and they are NOT cross compatible... you can NOT mix the various types. There are PAG, Ester, Mineral etc... Do some research and fit what is going to work with your system and your refrigerant.

And to make matters even more interesting, you might want to get into the system and test the various connections, switches etc. before you go to the (expensive) trouble of piecing it back into working condition again. The main failure points (other than places that will leak - hoses, connections, condenser, evaporator), are the pressure switch (88645‑12020) and the thermal expansion valve (88515‑87004) may become blocked or fail.

The filter/dryer (88470‑14010, Napa Canada NTC A7988) is going to need to be replaced as well, you'd better line one of those up. They are often a part that is used a across a manufacturer's line of vehicles and are not hard to get and not too expensive.

If you're unfamiliar with A/C, you might want to do some reading, do the wrenching yourself, then take it to a shop that is very familiar with A/C to get the system leak tested and drawn down to by vacuum to test its integrity.

Once it's leak tested, vacuum checked, and ready to go - make sure you have installed the correct amount of oil and refrigerant and it should work perfectly.

Hope this helps a bit.

~John

PS: part numbers are for a 1989 BJ70

 

[Coolstream]

My BJ70's AC has just gone intermittant, most of the time I switch it on and nothing happens but then sometimes all of a sudden it starts blowing cold. When it starts working I hear a screeching noise then the noise goes away. Does this sound familiar to anyone?

The first thing to check is the condition and tension of the belt. A loose belt can slip on the pulley, resulting in the screeching noise you're hearing. With the engine off, try rotating the front hub of the compressor by hand. It should turn with some resistance. If it won't turn, then it's time to replace the compressor and drier at the minimum. If the hub will turn, assuming it's still R12, when the A/C is operating look at the sight-glass on the top of the drier, and see if there are bubbles visable. If so, the system is low on refrigerant. If it's clear, the system has a full charge. If the operation is still intermittant, there could be an electrical issue preventing the compressor from engaging. Gauge readings would be helpful, both static pressure and when the A/C is operating.