Operation; Sequence Of Operation - Friedrich VERT-I-PAK VHA09K25RTQ Service Manual

Sequence of Operation

Power-up
When power is applied to the unit (230 VAC), L1 and L2 provide power to energize all relays, contactors, and control boards receive
power. 1 leg of the compressor is energized. Power is supplied to the transformer which provides 24 VAC to the thermostat and the
defrost control board.
When power is applied to the unit (265 VAC), L1 and L2 provide power to the heater relays, the main transformer which steps down
the voltage from 265 VAC to 230 VAC. 230 VAC energizes all other relays, contactors, and control boards. 1 leg of the compressor is
energized. Power is supplied to the secondary transformer which provides 24 VAC to the thermostat and the defrost control board.
When power is first applied to the Defrost control board, the defrost timers are reset and the short cycle timer is cleared. All
defrost mode calibration is cleared when power is applied to the control. If the power to the control is interrupted for less than 20
milliseconds, the control shall resume operation at the same point in the timing cycle.
The control shall not change modes of operation due to a power interruption of less than 20 milliseconds. Relays may temporarily
drop out during the power interruption. Power interruptions greater than 100 milliseconds may reset the control as a power-up
sequence. Power interruptions of any duration are not to cause lockout.
Fan only mode
Thermostat sends a G signal to energize the indoor fan motor relay (IMR) closing contacts 2 and 4 providing power to the low voltage
tap on the indoor motor controller.
The indoor motor controller provides a constant low voltage dc signal for static operation.
Emergency Heat
If thermostat provides W2 signal to safety relay (SR) it will energize the safety relay which removes power to the compressor and
provides power to pin 5 of the indoor fan motor relay (IMR), which provides power to the LI pin on ID motor controller for low speed
ID fan operation.
Simultaneously power is provided to energize the heat relay (HR) and the defrost heat relay (DHR) so that L1 and L2 of the heater
legs are energized providing power to the electric heat strips. Basepan heat is also provided at this time.
Compressor Contactor Operation
Anti-Short Cycle Delay (ASCD)
The Anti-Short Cycle time Delay is 3-minutes. This delay is active at power up and when the compressor has been de-energized. The
ASCD will not be reset during the 30-second compressor delay time after reversing valve change of state.
Compressor Operation
If the control receives a call for compressor operation "Y", in heating or cooling, the compressor contactor output "Y out" will be
energized immediately, or immediately after the ASCD timer has expired, whichever occurs last. The control shall de-energize the
contactor output immediately when the "Y" signal is removed.
Enable Temperature
If the condenser coil temperature is above 35˚F, all defrost functions are disabled.
Ambient Sensor Failure Detection
If the ambient temperature sensor is detected as being open or shorted, the control will operate as shown in Table 5.2.4 Thermistor
resistance values greater than 280K ohms (below -35˚F) or resistance values less than 3.75K ohms (above 120˚F) measured on the
ambient sensor will trigger this failure condition.
Condenser Coil Sensor Failure Detection
If the coil temperature sensor is detected as being open or shorted, the control will operate as shown in Table 501 Thermistor
resistance values greater than 280K ohms (below -35˚F) or resistance values less than 3.75K ohms (above 120˚F) measured on the
coil sensor will trigger this failure condition.
Ambient probe Coil Probe
Bad Good
Bad Good
Good Bad
Good Bad
20

OPERATION

Ambient Temp Coil Temp
N/A ≤ 30˚F
N/A > 30˚F
≤ 42˚F N/A
> 42˚F N/A
Table 501 (Sensor Conditions)
Defrost Action
Begins after 60 minutes
accumulated run time
No defrost
Begins after 60 minutes
accumulated run time
No defrost
Defrost Termination
Time/Temp:
14 minutes or termination temperature
N/A
Time/Temp:
14 minutes
N/A