Pumping Down - PREVOST H3-41 Maintenance Manual

SECTION 22: HEATING AND AIR CONDITIONING
important that the oil level be adjusted to
the proper level.
5. Withdraw a sample of the compressor oil and
check its color, odor, and acidity, using
instructions supplied above. If the oil is
contaminated, change the oil and filter-dryer,
and repeat the procedure until the system is
clean.
Clean-out After Major Compressor Failure
1. Reclaim the refrigerant into a refrigerant
bottle through a filter-dryer to filter out
contaminants.
2. Remove the failed compressor and repair it if
possible.
3. Install new or repaired compressor.
4. Change the filter-dryer using prescribed
method.
5. Circulate clean R-134a with the reclaimer to
clean out many of the contaminants collected
in the coil valves, TXV (Thermal Expansion
Valve), solenoid valves, check valves, and
any other mechanical component that may
have collected contaminants.
6. Evacuate and charge the system normally.
7. Run the unit for 8 hours and monitor the
pressure drop across the filter-dryer. Also
check the liquid line dryer for signs of
restriction. If the pressure drop across the
filter-dryer exceeds 12 to 14 psig (82,75 to
96,5 kPa) with a 40°F (5°C) evaporator coil
temperature, stop the unit and change the
liquid line and suction line filter-dryer. After 4
or 5 hours of operation, stop the unit and
replace the filter-dryer.
8. After 8 hours of operation, stop the unit and
remove a sample of the compressor oil and
check its color, odor, and acidity, using
instructions supplied above. If the oil is
contaminated, replace the oil and repeat step
7. If the oil is not contaminated, change the
filter-dryer again and replace the moisture-
liquid indicator.
9. After approximately 7 days of operation,
recheck the compressor oil for cleanliness
and acidity.
6.5.4

Pumping Down

This procedure is intended to reduce refrigerant
loss, on the central system only, by isolating it in
64 PA1621 Maintenance Manual All Series | Revised February 2019
the compressor and the receiver tank, as well as
in their connecting line, in order to carry out
repairs on other sections of the air-conditioning
system (lines and components).
NOTE
Once this pull down procedure has been
properly done, any component from the outlet
hose on the receiver tank, the filter-dryer, the
liquid solenoid valves, the evaporators, the
expansion valves, and all lines associated with
them can be serviced,
evacuated.
It must be noted that there is STILL refrigerant
under pressure in the compressor, the
discharge lines, condenser, and receiver tank
and that these items cannot be serviced. To
service these items, it is required to recover
the refrigerant using a recovery unit.
CAUTION
The filter-dryer should be changed each time a
line in the system is opened.
NOTE
Before attempting
compressor and receiver tank, use a recovery
unit to remove refrigerant from the system.
WARNING
To prevent any injury, when air conditioning
system must be opened, refer to previous
paragraph "Precautions
Refrigerant" to prevent any injury.
NOTE
For this procedure to be done properly, it is
assumed the proper amount of refrigerant is in
the refrigeration system. If there is any doubt,
use a recovery unit to recover and weight the
amount of refrigerant in the system.
NOTE
On vehicles equipped with small HVAC system,
refer to "Sanden SD Compressor Service
then properly
any repair between
In Handling