BMW Repair: engine run warmer after reto fit R12 to R134, coolant level, fan clutch

Question
Josh;
 We just retro fitted the A/C from R12 to R134 and it runs and cools great,but the engine is running hotter. We also replaced the cylinder head.It runs around 190 without the A/C,but when we use it it runs hotter,around 200 to 210.Can you help? Is Retro fitting more complex than just replacing the Freon?

Answer
Vick,
 Actually it's not a simple replacement.  The oil that is used is different, and some compressors are not compatable with both refrigerants.  It seems that you are getting cool air, so at least the compressor is working correctly.  I would, however, add a oil-shot to the A/C lines, so it will work correctly.  To be honest, the lines would need to be put under a deep vacuum for an hour or so (maybe more) to pull out all humidity and air.  Once that's done most places will purge the lines with nitrogen, to help blow out any humidity left in the lines.

 Once that's done the Nitrogen is removed with a vacuum, and the refrigerant and oil is replaced.  

 The only thing I can really see wrong with your setup is the reciever/dryer.  There is a dessicant inside that cleans the refrigerant and removes contaminants.  The old R12 reciever/dryer may not work correctly with the R134.

 Well using the A/C will cause extra load on the engine, the engine will have to work harder to turn the compressor, and the engine should idle up slightly to compensate for this.  It will be especially apparent if the compressor isn't working, and there is no load on the engine.. the engine should idle at 1200rpm or so.

 I would check your fan clutch, coolant level, and make sure to turn the heat on and make sure all the air bubbles are out of the heater core.  Once this happens your coolant level will drop slightly, so refill it.  I would hold the engine at 2k rpm, and open the bleed screw on top of the thermostat housing to make sure all the air escapes the engine. this will allow the engine to run cooler once all the air is out.  Also make sure you have the right thermostat installed, there are ones to make the engine run warmer and cooler.

 Good luck,
 Josh