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jr811 08-10-2007 05:14 PM

79 450 SL A/c has been converted to R-134.
When you add R-134a to system - do you need to start motor?


KCM 08-11-2007 12:20 AM

When adding any refrigerant to the system, you will need to start the compressor to pull it in. The exception is if the system has been pulled down with vacuum and sometimes you can get one can in without doing this. You may need to jumper the low pressure switch in order to get the compressor to kick in. ALWAYS add it to the low pressure port (large hose). NEVER add it to the high pressure (small line) side. And turn the blower in the car to high for better heat transfer.

Be careful not to overfill the system as this can cause damage to the compressor or other components. With R-134a, you only add 80% to 85% of the charge of R-12. If you are just topping off the R-134a, you should have a set of pressure guages, or at least a low pressure guage. Low pressure will run anywhere from 25 psi to 45 psi, but I've found 30 to 35 to be the usual range. The high side may run near 300, so be careful.

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