Danfoss DHP-A Service Instructions Manual page 41

Cause
14. Blocked evaporator on the water
side.
15. Blocked evaporator on the refrig-
erant side.
Table 14. Problem – Alarm HP (high pressure switch)
Cause
1. Blocked strainer in the heating sys-
tem.
2. Air in the heating system.
3. Closed or partially closed thermo-
stats/valves in the heating system.
4. The circulation pump that is defec-
tive or has jammed.
5. Shut-off main tap in heating sys-
tem.
6. Cable break or loose cable to high
pressure switch.
Troubleshooting
If there is no strainer in the brine circuit,
there is a risk of dirt sticking in the evapo-
rator and blocking it. Unfortunately there
is no easy way of checking if the evapora-
tor is blocked.
You can carry out a test by allowing the
compressor and circulation pumps to
remain in operation. Check that the circu-
lation pumps work (for circ.pumps with a
bleed screw, unscrew it and feel if the
pump rotor rotates using a screwdriver).
Then read the temperature on both con-
nection pipes to the evaporator:
If the temperature difference is <1°C, the
evaporator is probably blocked.
If the temperature difference is 2-6℃, it is
probably not blocked.
If the temperature difference is >6°C, the
evaporator is probably blocked.
Using manometer apparatus and ther-
mometer, check that the unit's overheat-
ing is correct for the specific refrigerant.
Troubleshooting
Check that the strainer is not blocked.
Listen for air in the heat pump and heat-
ing system.
Check that the thermostats/valves in the
heating system are open.
Is there voltage to the circulation pump?
Check that the main tap is open.
•
Check that both cables are connected
to the pressure switch.
•
Using the buzzer, check that there are
no cable breaks. In order to do this,
disconnect the cables from the pres-
sure switch and circuit board.
Remedy
If the evaporator is thought to be
blocked, try flushing it. If this does not
work, it must be replaced
If the evaporator is thought to be
blocked by oil for example, try blowing
nitrogen through it to release the oil. If
this does not work, it must be replaced
Remedy
Clean the strainer if necessary.
Bleed the heating system according to
the installation instructions.
Open closed thermostats/valves.
In the control system's manual test menu
check that the circulation pump is active.
Check if there is voltage to the circula-
tion pump, if there is, and it does not run,
the circulation pump is jammed. If this is
the case, open the bleed screw and try to
release the paddle wheel using a screw-
driver for example (Does not apply to
heat pumps in the Opti).
If there is no voltage to the circulation
pump, check if there is voltage from the
I/O card, see wiring diagram. If there is
voltage from the I/O card, check the
components between the I/O card and
the circulation pump.
If a component is defective, replace it.
Open closed main tap.
If a cable has come loose, reconnect it.
If there is a cable break, replace the
cable.
Service instructions VMGFC302 – 39