Friedrich Kuhl KCM21A30A Service Manual page 33

OPERATION
Unit Heat Control Operation - HeatPump With Electric Heat
This heating is more complex due to the possibility of two heating methods. If the ambient indoor temperature
is below the heat demand threshold (1.5˚F below the heat set point temperature), and the compressor is not
locked out, turn on compressor. If the ambient indoor temperature is .25˚F above the heat set point turn off the
compressor..
Figure 344 Heat Control (Heat Pump & Electric Heat)
If the compressor is locked out & electric heat is available:
1. Turn on the electric heat until the compressor is not locked out.
2. After lockout, turn off the electric heat, wait 5 seconds, then turn on the compressor.
If Electric Heat is Available:After the Heat button is initially pressed, the unit will run the electric heater first until the initial
set point is satisfied (Hot Start Feature). After the initial start, the unit will switch to Heat Pump heat and decide between Heat
Pump heat and Electric heat based on the following two monitored conditions:
Condition 1
If the outdoor coil temperature sensor drops to 30 ˚F or less for 2 consecutive minutes, the unit will switch to electric heat
if available. Thereafter, the unit will switch back to Heat Pump heat if the outdoor coil temperature sensor rises to 45 ˚F or
greater.
If Electric Heat is not available (out of order) and the outdoor coil temperature sensor drops to 30 ˚F or less for 2 consecutive
minutes, then the compressor and fan will turn off. Thereafter, the unit will switch back to Heat Pump heat if the outdoor coil
temperature rises to 45 ˚F or greater.
Condition 2
If the delta (set point temperature minus the ambient indoor temperature) is greater than 5 ˚F, then the unit will switch to
electric heat, if available. The unit will continue to operate with electric heat until the heat demand is satisfied. Note that the
electric heat switches on after the delta temp passes 5°F and the heat pump switches off. Also note that the electric heat will
run until the heat demand is satisfied. When another heat demand cycle is initiated, the heat pump will run unless the delta
temp is greater than the electric heat threshold.
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