Hi Peter, Sorry for the confusion. Let me clarify what was done. The system did not work when I bought the car in the winter. I shorted the switch to see if the compressor would run at all, which it did, and it was quiet too. I put gauges on it and there was some pressure in the system, it was just low. We evacuated the system and then pressurized it with 300psi of dry nitrogen, shut off the gauges, and let it sit for about 3-4 hours, no loss in pressure meant no big leaks. We then pulled vaccum with a proper vac pump (29.x" vacuum) for a good hour or more. Then the system was charged with the specified 2.4lbs of R-12 from a tank with a digital scale.
After all that the compressor didn't run... turns out the pressure safety switch was kaput! I shorted it and voila, working AC. I wasn't about to discard a full charge of R-12 just to change the silly switch. If/when the system loses enough charge to affect performance (hopefully a few years from now), then I will replace the switch the next time I need to open up the system. I'm not crazy about running it without the safety, but it will have to do for now. :-) -Dave M. > ------------------------------ > Date: Wed, 10 Aug 2005 17:44:23 -0500 > From: Peter Frederick <[EMAIL PROTECTED]> > Subject: Re: [MBZ] W124 A/C question - compressor cuts off too soon? > > Bypassing the low pressure switch will cause the compressor to run any > time the PBCU calls for it, although it will still switch off as > evaporator temp drops or it is cycled for temp control. The low > pressure switch on protects against inadequate freon (and no compressor > lubrication). Do not leave it shorted, if it's low, get it pumped out > and fix the leak, then replace the switch and properly recharge. > > I heat the cans of freon in some hot tap water (only as hot as the > water heater delivers it!) making sure the can stays upright. If you > leave it at room temp, it can take forever to transfer because the low > side pressure is too high. > > I would strongly recommend against adding freon to a system without a > working gauge set -- it's fairly easy to add too much and blow a high > side hose! > > Peter
