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cycling condenser fan

Fixin der Porsche on Thu June 03, 2010 9:17 PM User is offline

Year: 1983
Make: Mercedes
Model: 300sd
Engine Size: 3.0L
Refrigerant Type: r134 conversion
Ambient Temp: 90
Pressure Low: 45
Pressure High: 285
Country of Origin: United States

Just finished replacing the evaporator and heater core on this car (days of work) charged it up working fine. Today I let it idle in the Texas sun for a final check with max cooling temp selected, max interior fan speed, doors closed, and noticed the condenser fan cycling ON for several seconds 8-15 then OFF for anywhere between 3 and 30 secs. Before in max cooling mode the condenser fan just came on, and stayed on after it hit 225 psi high side. Is it over heating and switching itself off until a bi-metal switch closes again? Switching the control relay with another one does not help. Bad bearings?

TRB on Fri June 04, 2010 9:46 AM User is offlineView users profile

If it is a bad bearing you should be able to remove the fan housing and feel the resistance when spinning the fan. Never have been a fan of Mercedes R134a conversions. Would not be surprised if the high side is going through the roof at high idle.


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Fixin der Porsche on Fri June 04, 2010 7:20 PM User is offline

High side pressures never get beyond 300 psi even at 3000rpm. Disconnected condenser fan from system and powered it directly to 12v runs continuously, checked the power at the dryer switch, 12v so the aux fan switch is fine. Swapped aux fan relays with a known working one, made no difference, so I am stumped.

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