Heat pump charge

Question: I am trying to determine whether a heat pump has a correct charge. I usually use subcooling and superheat to determine this. However the unit has a condenser fan cycling control. This control was installed so that the unit could be used for space cooling even in winter.

The control is piped into the high side. With this arrangement, head pressure, and suction pressure vary, and I don't know what values to use for calculating superheat and subcooling.

-Olin Zuercher, Elkhart, IN

Answer: In reference to charging a heat pump (or air conditioner) using the superheat/subcooling methods, the fact that any outdoor fan cycling control is used on the unit does not change the basic charging procedure.

We recommend using the superheat/subcooling method in the cooling mode at outdoor ambient temperature at or above 60 ° F. While charging the unit, simply bypass the load head pressure cutout and charge the unit as you normally would. Below 60 ° F, the fan would be cycling quite a lot. However, at these temperatures, you would need to use an alternative method of charging, such as weighing the charge.

-Charles Whitaker, SnyderGeneral