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Heat Controller, Inc. VMH SerieS Service Manual
9.3.2.7 Low pressure protection (ODU P2) (Only for A-VMH36QC-1)
Replace outdoor main board
Evacuate the refrigerant, then use
high pressure nitrogen or refrigerant
to blow out pipe, vacuum and
recharge with refrigerant again
Find the leak by charging nitrogen or refrigerant
into the system, if the leak is serious there will be
distinct “hissing” sound; if the leakage is small, use a
soap and water mixture or electronic leak detector
to nd the leak and repair.
Stop the unit
Replace low pressure protector
Reconnect it properly
No
Low pressure protection
Is the wiring between the
low pressure protector
and main control board
connected correctly?
No
Yes
Yes
Yes
Yes
Is the low pressure
protector broken?
Short circuit the low
pressure protector socket,
check whether the system
can run normally now?
Check whether
the refrigerant
system is ok
Check whether the
outdoor ambient
temperature is to low
Check if there is
a refrigerant leak
Connect the pressure gauge to
the gauge joint of the system,
check whether the pressure is
lower than 0.14MPa
Check whether the
refrigerant circuit is
blocked or not
No
No
No
Yes
Yes