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Marvair Classic AVPA/HVPA/HVPSA Heat Pump I&O Manual
11/2017 Rev. 7
to open. When the “G” signal is not present, the control will energize the Damper Relay Closed terminal
to close the damper. When “No” is selected, this feature is disabled. The factory setting for the damper
relay option is “No”.
Defrost Mode
The board has an integral defrost cycle that will be initiated by the Defrost Sensor (DS). If the defrost
sensor registers a temperature of 32°F while in the heat mode, it will initiate a pin selectable 30, 60, or
90 minute delay. The factory setting is 60 minutes. If the sensor is still calling for defrost at the end of
this delay, it will de-energize the outdoor fan, energize the reversing valve through the RV terminals, and
keep the compressor energized. The defrost cycle will terminate on time or temperature. It will have a
maximum defrost run time of 10 minutes, however, if the defrost sensor registers a temperature of 50°F
or higher before the 10 minute maximum run time, the defrost cycle will terminate. If “Yes” has been
selected for Electric Heat During Defrost (EHDD) and “No” selected for the S-Circuit, the electric heat
(EH) output will be energized during a defrost cycle to supply heat while the coil defrosts.
Electric Heat During Defrost (EHDD)
The board provides the option of running the electric heat (EH) during a defrost cycle. There are two
options for the EHDD, “Yes” and “No”. If “Yes” is selected, the board will energize the EH terminals
during a defrost cycle. If “No” is selected, the EH terminals will not be energized during a defrost cycle.
The factory setting for EHDD is “No”. If the S-circuit is in the “Yes” position, the EHDD function will
be disabled.
S-Circuit
The S-Circuit prevents the compressor and electric heat from operating simultaneously. The S-Circuit
is pin selectable using a jumper to select “Yes” to enable this feature or “No” to disable it. When “Yes”
is selected, the control will not allow the compressor to run when there is a call for electric heat at the
W2 input. It will turn the compressor off until the call for W2 is satisfied. The factory setting for the
S-Circuit is “No”.
Test Mode
A jumper selectable test mode can be used by technicians for trouble shooting purposes. The test mode
reduces the delay on make and anti-short cycle timers to ten seconds, and the LPS bypass becomes two
minutes.
Internal Head Pressure Control (Requires optional coil sensor)
The control has an internal, fixed set point head pressure control designed to maintain a constant head
pressure under low ambient conditions. It will monitor a coil sensor that is inserted into the condenser fan
coil and modulate the speed of the fan motor accordingly to maintain a constant coil temperature in turn
stabilizing the head pressure. The fixed set point that the control will maintain is 100°F. The motor will
have a minimum operating speed of 20%-30% of the full speed. It will also incorporate a fixed hard start
time of one second during which the condenser fan motor will turn on full speed for one second at start up.
High Pressure Switch (HPS)
The high pressure switch is mounted on the compressor liquid line. The HPS terminals are on the high
pressure switch input. This input monitors the status of the high pressure switch and determines when
this fault condition is present. If the HPS is open on the initial “Y” call, the control board will not allow
the compressor to operate. If the HPS opens while the compressor is running, the control board will turn
