Friedrich VERT-I-PAK VHA-18K75RTP, Service & Parts Manual

Page: 22 / 103

22 PB
Operation
Electronic Sequence of Operation
Compressor and Reversing Valve Control
Active Mode Compressor Reversing Valve
Cooling On De-Energized
Heat - Pump On Energized
Heat - Electric Off
Fan Only Off
Reversing Valve
The reversing valve stays in the last state until a call for heat or cooling.
The reversing valve only changes when required to provide coooling or heat pump. Leave the reversing valve in it’s last state
until it’s required to change
.
Unit Cooling Mode
Once the ambient temperature rises past the cool demand set point of the t-stat (see figure below), and the
compressor is not locked out, the cooling cycle begins. As shown in the figure below, the fan is started 5 seconds
prior to the compressor. Once the ambient temperature has been lowered to the cool set point, the cooling cycle
starts to terminate by shutting off the compressor. After a 30 seconds delay, the fan is shut off.
Heating Mode Control Operation
There are two heating methods: Heat Pump and Electric Resistance Heat.
There are 2 Types of units that provide heating:
Cool / Heat Pump with Electric Heat and Cool with Electric heat.
Heat Mode in Cool with Electric Heat Units
When the t-stat is in the Heat Mode, if the indoor ambient temperature is below the heat set point, the fan turns on 5 sec-
onds prior then the electric heat will turn on. When the t-stat is satisfied, the electric heat will turn off. The fan turns off 15
seconds later.
Heat Pump With Electric Heat Operation
This heating has two heating methods. If the ambient indoor temperature is below the heat set point and the compressor is
not locked out, the compressor turns on. If the ambient temperature rises above the t-stat’s heat set point, the compressor
turns off.
If the Compressor is Locked Out on the 3 Minute Time Delay and Electric Heat is Available
1. The control turns on the electric heat until the compressor is not locked out.
2. After lockout, the control turns off the electric heat, waits 5 seconds, then turns on the compressor.(The wired
remote wall t-stat’s time delay may override this feature).
Condition 1
I
f the outdoor coil temperature sensor drops to 30 degrees F for less than 2 consecutive minutes, the unit will switch to elec-
tric heat if available. Thereafter, the unit will switch back to Heat Pump heat until the outdoor coil temperature sensor rises
to 45 degrees F or greater.