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Marvair Wall Mount H/P MAA1020H-1048H/MGA1072H I&O Manual
02/2021 Rev.2
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
the compressor off, register the first HPS fault, and initiate the 3 minute anti-short cycle timer. If two
HPS faults occur within a one hour period, the control will enter a HPS lockout condition and energize
the alarm contacts. The RED status LED will blink once to indicate this condition. The lockout condition
will only be reset by manually cycling power to the control to prevent destructive short cycling. To reset
the switch, turn primary power off, then back on or turn thermostat system switch off, then back on.
The high pressure switch opens at 650 psig and closes at 450 psig.
Loss of Charge Switch (LPS)
The loss of charge switch is mounted on the compressor’s liquid line. The LPS terminals are the loss
of charge switch input. This input will be used to monitor the status of the loss of charge switch and
determine when a LPS fault is recognized. There is 3 minute loss of charge switch bypass timer. If the
LPS is open on the initial “Y” call or while the compressor is running, the control will ignore the status
of the LPS and not recognize a fault for 3 minutes. If the LPS is still open after 3 minutes, the control
will de-energize the compressor, register the first LPS fault, and initiate the 3 minute anti-short cycle
timer. If two LPS faults occur within a one hour period, the control will enter a LPS lockout condition
and energize the alarm contacts. The RED status LED will blink twice to indicate this condition. The
lockout condition will only be reset by manually cycling power to the control. To reset the switch, turn
primary power off, then back on or turn thermostat system switch off, then back on.
The loss of charge switch opens at 40 psig and closes at 60 psig.
Status LED Blink Codes
There are two LEDs on the board. The green LED is used as a power indicator. The red LED is used to
indicate the two fault lockout conditions. During a HPS lockout, the red LED blinks once. During a LPS
lockout, the red LED blinks twice.
Color
Type
Status
Description
Green
Power
Constant On
24 VAC power has been applied
Green
Status
Constant On
Normal Operation
Red
Status
1 Blink
High pressure switch has opened twice
Red
Status
2 Blinks
Loss of charge switch has opened twice
Red
Status
3 Blinks
Freeze Condition
Red
Status
4 Blinks
Faulty or disconnected defrost sensor
Led Color Type Status Description
Board Inputs
R and C
. The R and C terminals are the input power terminals for the control. They will accept any
voltage between 19-32 VAC.
Y
The “Y” terminal is the compressor input from the thermostat. Given that all time delay and fault
conditions are satisfied, the control will energize the compressor contactor through the “CC” terminals
when there is a 24 VAC signal present at the “Y” terminal.
