PREVOST H3-41 Maintenance Manual page 939

Manual ".
Procedure
1. Energize driver's unit and passengers' unit
(main HVAC system) section liquid solenoid
valve. To do so, connect male and female
connector housings of C24 together for the
passengers' area (found on the HVAC
module in evaporator compartment) and
C44 for the driver's area (located on the
ceiling of the spare wheel compartment).
During normal use, both male and female
housings of connector C24 and C44 are
kept unplugged.
CAUTION
Connectors C24 & C44 must be disconnected
and their caps reinstalled after this procedure.
Leaving them connected will keep the driver's,
passengers and overhead compartment liquid
solenoid valves open, and result in battery
draining if the vehicle remains unused for
several days.
FIGURE 80: COMPRESSOR
BACKSEATED POSITION
POSITION)
FIGURE 81: COMPRESSOR SHUT-OFF VALVE IN FRONT
SEATED POSITION
SHUT-OFF VALVE
(NORMAL OPERATING
PA1621 Maintenance Manual All Series | Revised February 2019
SECTION 22: HEATING AND AIR CONDITIONING
2. Run the system for 10 minutes and then
shut it off.
3. Close (frontseat) the receiver tank outlet
shutoff valve by turning the stem clockwise
(Figure 47 and Figure 81).
MAX TORQUE: 21 lb-ft (28 Nm)
4. Backseat the compressor suction shutoff
valve (FIGURE 80).
MAX TORQUE: 12 lb-ft (16 Nm)
5. Install an appropriate pressure gauge set on
the service port and then turn the shutoff
valve forward ¼ turn more or less until a
visual check of the suction pressure is
possible.
6. Disconnect the low pressure transducer.
The multiplex system will establish a default
value of 34 psig and this will allow pulling
down the A/C compressor to 0 psig. Note:
the low pressure transducer must be
reconnected after the pumping down
operation is complete.
7. Run the A/C compressor until suction
pressure is pulled down to 0 psig.
8. Disconnect the compressor clutch to stop
the compressor from pulling the system into
a vacuum. Vacuum is not required. The
pressure will probably slowly increase on the
suction side. When it reaches 10 psig,
reconnect the clutch and repeat the pull
down to pull down this residual pressure.
This process might need to be repeated a
couple of times until the suction pressure
drops and remains to 0 psig.
9. Stop the compressor.
10. Close (frontseat) the suction shutoff valve on
the compressor (Figure 81).
MAX TORQUE: 21 lb-ft (28 Nm)
11. At this point, C24 can be disconnected to
isolate the section of the system located
between the receiver tank outlet shutoff
valve and the passengers' unit liquid
solenoid valve. Doing so would be useful to
perform replacement of the filter-dryer for
example.
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