condensor fan cycles on and off

[randymanc69]

Condensor fan motor cycling on and off, but charge is good and just replaced board. Any ideas?

[hvacrmedic]

Fan cycle control?

[SuperTech2010]

how do ya know if charge is good if fan is off and on? what kind of system is this split HP, RTU, low ambient A/C, cooler? is there continuous voltage to the motor?or does it drop out because of a fan cycle control?

[aggiechillertech]

Sounds like it has a low ambient kit installed on it.

[randymanc69]

It is a split HP running in heat mode.

[BaldLoonie]

Early Carrier Puron units did this in mild weather.

[john_dixon29]

Yeah it's called a vapor pressure switch and if I remember correctly it is on the suction line past the RV. In the schematic it is labeled VPS. I never found any literate explaining what its purpose was but I assume it kills the OD fan motor while running in HP mode during moderate ambient conditions, which brings down the suction and in turn will lower the head. Does anyone know it's actual purpose? And what are it's open and close set points.

[BaldLoonie]

which brings down the suction and in turn will lower the head. Does anyone know it's actual purpose?

You answered your own question. To keep pressures down in mild weather. Carrier did it with early Puron units. It's suggested with high velocity air handlers with any units just because they have such low airflow. With 200 CFM/ton, the HV air handlers could have head pressures tripping pressure switches or internal relief if calling for heat when it is fairly mild out.

[pony]

so it is normal?how often it cycle on and off?randymanc?