Operational Problems - Danfoss DHP-AQ Series Service Instructions Manual

Service Instructions
Pressure switch/pressure transmitter
Refrigerant R407C
OP (operating pressure switch)
High pressure switch
Pressure transmitter low pressure
Following parameters can be read off in the display:
▪ Suction gas temperature
▪ Evaporation pressure
▪ Evaporation temperature (calculated from "Dew point")
▪ Opening percent EXV
▪ Superheating
This means new opportunities to diagnose the heat pump, without having to remove the covers when working on the cooling circuit.
▪ In normal operation the heat pump operates with superheating of 5.5°C – 7°C, the expansion valve's degree of opening will vary
depending on operating situation.
▪ At outdoor temperatures of -5°C or lower the opening degree is below 20%
▪ At outdoor temperatures of +5C to +13°C the opening degree is around 40-50%
▪ When cooling (A35W18) the degree of opening is 100%
If superheating is >9°C and the degree of opening of the expansion valve lies steady at 100% this can indicate
Caution
that a significant part of the refrigerant has leaked from the heat pump.
If this is the case, the heat pump must be checked by service technicians with personal refrigeration
certificates!
3.5

Operational problems

The tables list the most probable and common causes of the problem first. When troubleshooting the cause of a problem start with the
first cause and go down the list.
There may be more than one way of troubleshooting a cause where the most probable is given first.
3.5.1 Alarm
Problem – Alarm LP (lower pressure transmitter)
Cause
1. Cable break or loose cable
to lower pressure transmit-
ter.
2. The pressure transmitter
opens too soon.
3. Lack of refrigerant, not
enough refrigerant in the
system.
Danfoss Heating Solutions
DHP-AQ
Break pressure
2.85 MPa
3,10 MPa
0.04 MPa
Troubleshooting
▪ Check that both cables are connected to the lower
pressure transmitter.
▪ Using the buzzer, check that there are no cable
breaks. In order to do this, disconnect the cables from
the lower pressure transmitter and circuit board.
Pressure transmitter fault, opens at a higher pressure than
indicated. Check break pressure using the manometer ap-
paratus.
Using manometer apparatus and thermometer, check that
the unit's overheating is correct for the specific refrigerant.
Remedy
If a cable has come loose, reconnect it.
If there is a cable break, replace the cable.
If the pressure transmitter breaks too early,
replace it.
Follow the correct procedure (depending
on type of refrigerant) to add the correct
amount of refrigerant.
If there appears to be a leak in the refriger-
ant circuit, carry out leak tracing and any
necessary corrective action.
VMGFJ202
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