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Head Pressure Control Valves, Series
Troubleshooting
Complaint
1. Low Condensing Pressure
during operation
2. System runs high condensing pressure
or cycles on high pressure cut-out
3. System fails to start or short cycles on
low pressure failure switch after off-cycle
or defrost
HP___65059__R03.doc Replacement for __R02
Operating Instructions
HP
Possible Cause
Valve unable to throttle Port C because:
Foreign material wedged between Port C seat and seat
disc
Power element lost charge
Insufficient wintertime system charge
Wrong charge pressure in valve for system refrigerant
Receiver exposed to low ambient acting as a condenser Insulate receiver
Hot gas bypass line restricted or shut-off
Compressor not pumping or restriction in liquid line, or
low side causing very low suction pressure
Condenser fan(s) not running or turning wrong
direction
Fan cycling
Pressure drop through condenser exceeds 1,4 bar
forcing port C partially open
Condenser undersized or air flow restricted or short
circuiting
B port wedged open due to foreign material between
seat and seat disc
B port seat damaged due to foreign material
Wrong charge pressure in valve for system refrigerant
Excess system charge or air in system
Obstruction or valve closed in discharge or condenser
drain line
Liquid line solenoid valve fails to open
Receiver exposed to low ambient on outdoor
condensing unit during off-cycle or defrost
Thermo valve fails to feed due to loss of charge or
other reason
Oil pump failing to develop oil pressure due to viscous
oil in exposed crankcase
Liquid solenoid valve failing to open or thermostat fails
to make contact
Defrost control fails to terminate defrost
Receiver pressure approaching low pressure control in
cut-in setting because:
Insufficient refrigerant to maintain some liquid in
receiver or remote condenser system during off-cycle
Oil congealing in low pressure control or oil pressure
failure. Switch cap tubes where exposed to low
ambient
Emerson Electric GmbH & Co. OHG
GB
Heerstr.111 – D-71332 Waiblingen
Tel.: 07151 509-0 - Fax.: -200
www.emersonclimate.eu
Artificially raise Condensing Pressure and tap valve
body to dislodge foreign material
Change valve.
Add refrigerant
Change valve
Clear obstruction or open valve
Change or repair compressor or clear obstruction or
other reason for low suction pressure
Replace or repair fan motor, belts, wiring or controls as
required
Run condenser fans continuously while system is
running
Re-pipe, re-circuit or change condenser as required to
reduce pressure drop
Increase size of condenser or remove air flow
restriction or short circuit as required
Artificially reduce condensing pressure and tap valve
body to dislodge foreign material
Change valve
Change valve
Purge refrigerant or non-condensables as required
Clear obstruction or open valve
Check solenoid valve
Shorten off-cycle time of defrost time if possible or add
receiver insulation. If long off-cycles are required
receiver heat may also be required. Time delay relay
may also be used.
Change or repair Thermo valve.
Add crankcase heater
Change or repair solenoid or thermostat.
Change or repair solenoid or thermostat.
Add refrigerant or optional check valve. Time delay
relay to by-pass LP control on start-up may also be
used. Set for 2-3 minutes forced run.
Change cap tube to ¼"/6mm copper tube.
Date: 20.07.2009
Corrective Action
PCN 861 376
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