7
Marvair ModPac Installation & Operation Manual
11/2017 Rev.8
Lock-out
If either of the fault conditions (LPS or HPS) occurs twice during the same call for cooling, the control
board will enter into and indicate the lockout mode. In the lockout mode, the compressor is turned off.
If there is a call for indoor air flow “G”, the blower remains energized, the alarm output is energized and
the status LED will blink to indicate which fault has occurred. When the lockout condition is cleared,
the unit will reset if the demand for the thermostat is removed or when the power is reset. With the
control board, the user can now have either normally closed or normally open contacts by moving a
wire on the control board. ComPac air conditioners are factory wired to be normally open.
Delay on Break
If the compressor is de-energized due to a loss of a cooling “Y” call or the first fault, the unit re-start
will be delayed 3 minutes from the time the contactor is de-energized. (Note: There is no delay on break
if the lockout condition is reset.)
Delay on Make
On initial power up only, the unit will wait 0.03 to 10 minutes from the cooling “Y” call before
allowing the contactor to energize. The delay can be adjusted by the DOM wheel on the board. Factory
recommended wait is 3 minutes.
Low Pressure By-Pass Time
When starting, the low pressure switch (LPS) fault condition will be by-passed for 3 minutes before
the contactor is de-energized.
Post Purge
Upon a call for indoor airflow “G” the blower will energize immediately. When in the cooling mode,
the blower will remain energized for 10 to 90 seconds (adjustable) after the compressor has been de-
energized. The time period can be changed by fan purge wheel on the board. Factory setting is 90 seconds.
LED Indicator Lights
COLOR
TYPE
STATUS
DESCRIPTION
Green
Power
Contstant On
24 VAC power has been applied
Red
Status
Contstant On
Normal operation
Red
Status
1 Blink
High pressure switch has opened twice
Red
Status
2 Blinks
Low pressure switch has opened twice
High Pressure Switch
The high pressure switch is mounted on the compressor liquid line. It is electrically connected to a
lockout relay which shuts down the system if the refrigerant pressure rises to 650 PSIG. This protects
the unit if airflow through the condenser is blocked or if the outdoor fan motor fails. Although the
contacts of the high pressure switch close when the refrigerant pressure falls to approximately 450 PSIG,
the system must be manually reset once the lockout relay is activated. A manual reset is necessary to
prevent harmful short-cycling. To reset switch, turn primary power off, then back on or turn thermostat
system switch off, then back on.
Low Pressure Switch
The low pressure switch is mounted on the compressor suction line. It is designed to open if the refrigerant
pressure drops to 40 PSIG; it resets when the pressure rises to 60 PSIG. The switch protects the unit if
airflow through the indoor blower is impeded, if the blower motor fails, or if there is a loss of refrigerant.
