Replacement Of The Filter-Dryer After Pumping Down; Moisture Indicator - PREVOST H3-41 Maintenance Manual

4.7 FILTER-DRYER
A filter-dryer, also located in the condenser
compartment, is installed on the liquid refrigerant
line after the receiver tank. It is used to absorb
moisture and foreign matter from refrigerant
before it reaches the expansion valves.
The filter-dryer should be replaced after a
severe system failure, after a prolonged
exposure and most important, when the
moisture indicator sight glass turns to pink.
4.7.1 Replacement Of The Filter-Dryer After
Pumping Down
The filter-dryer is of the disposable type. When
replacement is required, remove and discard the
complete unit and replace with a new unit of the
same type according to this procedure:
1. Perform the pumping down procedure to
isolate refrigerant in the receiver tank.
2. Disconnect C24 to isolate the section of the
system located between the receiver tank
outlet shutoff valve and the passengers unit
liquid solenoid valve.
3. Change the filter-dryer.
FIGURE 49: ISOLATED SECTION X3 SERIES
4. Once the filter-dryer has been replaced, it is
necessary to evacuate the opened section
of the refrigerant circuit. Evacuate the
isolated section of the system using a
vacuum pump connected to the service port
of the receiver outlet shutoff valve.
5. Evacuate the section of the refrigerant
piping as needed and in accordance with
best practices, using a micron gauge to
monitor the depth of vacuum. Evacuate to a
system pressure less than 1000 microns.
SECTION 22: HEATING AND AIR CONDITIONING
6. Turn off the vacuum pump.
7. Backseat the outlet shutoff valve and then
disconnect the vacuum pump hose.
Do not use carbon tetrachloride or similar
solvents to clean parts. Do not use steam
gun. Use mineral spirits or naphtha. All parts
should be thoroughly cleaned.
brush to wash dirt from grooves, holes, etc.
Cleaning products are flammable and may
explode under certain conditions.
handle in a well ventilated area.
4.8

MOISTURE INDICATOR

The moisture sensitive element consists of a
color changing ring which is reversible from pink
to blue and vice versa as the moisture content in
the refrigerant changes.
Since temperature changes affect the solubility,
color change will also vary with the refrigerant
temperature. The above table shows the color
change for R-134a at various moisture levels
and liquid line refrigerant temperatures.
Check refrigerant moisture indicator at the
intervals specified by the Lubrication And
Servicing
LUBRICATION & SERVICING.
Replace filter-dryer unit according to moisture
indicator
PA1621 Maintenance Manual All Series | Revised February 2019
CAUTION
DANGER
• PINK: high
moisture detected.
• PURPLE
levels of moisture detected.
•
BLUE:
operating conditions.
MAINTENANCE
Schedule in
Use a stiff
Always
levels of
(caution): low
dry, optimal
Section 24:
35