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

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26 PB
OPERATION
Unit Heat Control Operation - Heat Pump With Electric Heat
Automatic Emergency Heat
If the sealed system fails with a bad reversing valve or anything that causes the indoor coil to get colder than the
indoor ambient temperature:
1) If the indoor coil thermistor senses a 5 degree temperature drop as compared to the ambient temperature
thermistor and this lasts up to 5 minutes, the control board will switch the unit to electric heat and continue
heating with it.
2) At this point, error code 15 is generated; heat pump failure. Indoor coil temperature lower than indoor ambient
temperature for 5 or more degrees for 5 consecutive minutes.
Note: It is Ok to continue to use the unit with the electric heater until the heat pump is repaired.
Heat Control Operation - Electric Heat Only
When in the Heat mode, with and without Fan Mode Auto (Fan cycling):
If the indoor ambient temperature is below the Heat Demand Threshold (Heat Set Point minus 1.5 ˚F), turn on
electric heat. If Ambient is 0.3 ˚F above the Heat Set Point turn off the electric heat.
System Mode Auto
This mode provides automatic change over between cool and heat. The auto mode runs based on the room ambient
temperature vs. the Demand Thresholds. It is only available in Heat-Cool Unit.
Notes:
There is a buffer zone between the cool and heat set points where no heating or cooling is allowed to occur. It is
critical that the Cool Demand Threshold be greater than the Heat Demand Threshold by a minimum of 3° while
in the Auto System Mode. For example, if a user enters a value for the Auto Cooling Set Point that violates the
minimum delta 3° rule, the Auto Heating Set Point will adjust accordingly.
Automatic Change Over Delay (Cool with Heat Units)
The change over delay ensures that any system heating or cooling over shoot does not trigger an opposite demand
cycle. The change over delay = 15 min. This timer blocks the opposite demand cycle from running until the timer
expires. As an example, if the last demand was a cool cycle, and another cool cycle is requested, the timer will not
block the request. However, if the last demand cycle was a cool cycle, and heat cycle is requested, the timer will
block the request until the change over delay is expired.
Compressor Lock Out Time
The lockout feature ensures that the compressor is de-energized for a period of time. The timer varies randomly
from 180 to 240 seconds
The compressor lockout is initiated every time the compressor is “off” due to:
(1) Satisfying the temperature set point
(2) Changing mode to fan only or heat
(3) Turning the unit off
(4) Control is first plugged in or power is restored after failure
(5) Line power is restored from a brown out condition
Cooling Fan Delay
Fan cycle/Auto mode only
When unit cycles cooling ON – starts the fan 5 seconds EARLY. When unit cycles cooling OFF – DELAYS the fan off
for 30 seconds.