Low Head Pressure

For air-cooled condensing units, when the head pressure control system is faulty or improperly adjusted. All air-cooled condensers are sized for a given ambient air temperature, usually 90-95°F. When ambient temperatures drop below 50°F, the condenser will be over-sized and some type of head pressure control is needed.

Probable cause: Remedy:
Fan cycling/variable speed fan no longer effective due to low ambient temperature and/or prevailing winds.

  1. Improperly set (cycling off, too late/too late high of a speed setting).
  2. Mis-wired.
Find the source of the problem and correct.
Install flooding type head pressure control.

  1. Base the fan cycling on the ambient temperature with pressure override.
  2. Find the source of the problem and correct.
Damper control.

  1. Mis-wired.
  2. Defective components.
  3. Mechanically kept open (broken or something jammed to keep them open).
  4. Incorrect setting (starts closing too late).
 Find the source of the problem and correct.
Note: Damper control is not recommended for use on refrigeration units when the condenser is exposed to ambient temperatures below 32°F
Flooded head pressure control system.

  1. Pressure setting too low.
  2. Defective components.
  3. Constant pressure valve head, losses its charge.
  4. Differential check installed backwards on a two valve system.
  5. Loss of liquid seal in receiver due to insufficient charge for winter operation.
Find the source of the problem and correct.

  1. Adjust pressure setting to desired level.
  2. Replace defective components.
  3. Charging method
  4. Install valves in the correct direction.
  5. Add additional refrigerant for proper system performance