20 minute air condition
 

1989 300e with nippocondenso 10p15c compressor.
What would cause the compressor clutch to slip/stop turning when hot. AC will blow cold air for approximately 20 minutes and then clutch quit turning and ac begins to blow warm, then once you cut off ac and wait about 20 minutes and turn it back on it blows cold again for another twenty minutes and the cycle goes on like this. Whats wrong with it.

Bad belt (unlikely, that usualy requires re-starting car) or coolant temp going too high. Check aux fan and visco clutch, also radiator for blockages.

High coolant temp (over 110C) will shut the AC compressor off.

Could also be a bad Kilma relay, but you need to check the inputs before replacing it.

Peter

Loose belt...due to bad tensioner.
 

Good luck!

Thanks for all the input, belt is tight, coolant temperature runs at 80 to 85 max, radiator good, klima relay replaced with no change so I reinstall old relay. How do you check the visco clutch.

if coolant temp is 80-85C then viscous fan is good- doing it's job. Next time compressor cuts off - check the belt tension when it cuts off and when it works (engine off of course) Try twisting the belt sideways with your thumb and forefinger at a convenient place and see if there is more twist when the a/c cuts off than when it runs - if there is more twist when it cuts off - change the belt tensioner.

Tensioner was replaced a little over a year ago, will check belt tomorrow. Thanks.

While no expert, it may be a low refridgerant charge. I know that too little charge will "cut-off" the compressor. If you have the correct manifold gauge set (134a or R12) you can check the system pressures when operating properly, and again when the system is inoperable. I cannot account as to why the system works for so long before failing, but I have seen systems that work for a few minutes and then cut out. Hope this helps.

This sounds suspiciously like the RPM sensor on the back of the compressor is sending out a bogus signal, which the relay interprets as engine RPM and compressor RPM out of sync, and shuts the compressor down.

Do a search on "klima hack" for a solution.