Thread: Nice cool AC
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Old 07-07-2003, 10:07 AM
jcyuhn jcyuhn is offline
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Join Date: Jun 2000
Location: Plano, TX
Posts: 2,476
Good job on the changeout. There's nothing like the satisfaction of a nice, cool breeze on a hot day

Changing the condenser and radiator fans isn't going to do much for idle performance on this car. The main problem is the a/c compressor - it's too small (displacement-wise) and turns too slowly. It simply doesn't "pump" enough at idle. This can be observed with a set of gauges. On my 1987 300TD (same compressor) the low side pressure rises to 45-50 at idle. (It's about 25 at 1500RPM, which is just where you want it.) Evaporator temperature is directly related to low side pressure - with R-12 it's pretty much the same as the pressure. So this means the evap is 50 degrees at idle. Broad rule of thumb is that discharge air is ten degrees warmer than the evaporator, so 60 degree vent air at idle. A better condenser will lower the high side pressure - not a bad thing at all - but without a change in low side pressure you won't see any better performance at idle.

- JimY
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