Friedrich SS08M10 Service & Parts Manual page 25

Heating Mode Control Operation
There are two heating methods: Heat Pump and Electric Resistance Heat.
There are 3 types of units that provide heating: Heat Pump Only (Model YS10M10)
Heat Pump with Electric Heat and Cool with Electric Heat.
Heat Control Operation Heat Pump Only Unit (YS10M10 has no electric heat back-up)
Once the ambient temperature falls below the Heating Demand Threshold
(1.5 ˚F Below the Heat Set Point Temperature), the heating cycle begins. The fan is turned on 5 seconds before.
Once the ambient temperature has been raised to the Heat Satisfied Point (Set point + .25 ˚F), the compressor is
turned off. The fan is turned off 15 seconds later. The figure below illustrates the basic heat pump operation.
Satisfied Point
Heat Control (Heat Pump Only)
YS10M10 Heat Pump Defrost Cycle Operation
The defrost in this unit is an active reverse cycle. The defrost control runs in the background and determines when a
defrost cycle is required. Once initiated, the defrost cycle runs to completion.
The defrost cycle can only be initiated when the heat pump is in operation. The compressor will not be turned off to
avoid activating the compressor's time delay. The reversing valve will be switched to the cool mode position. The
indoor fan/blower will be turned off. Once the defrost cycle is finished, the system should re-enter a heating demand
cycle if required.
When the heat pump run time is 60 minutes or greater with an outdoor coil temperature of 26F degrees or lower, the
control will run an active defrost for up to 6 minutes. When the temperature at the outdoor coil reaches 54F degrees,
the heat pump heat will resume.
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