PREVOST LE MIRAGE XLII BUS SHELLS, Maintenance Manual

Page: 1085 / 1260

Section 22: HEATING AND AIR CONDITIONING
PA1564
17
8. Wait until pressure gauge reaches 1 to 2 psi
(7 to 14 kPa). To accelerate procedure,
lightly open compressor suction valve until
pressure reaches this value.
8.4 ADDING REFRIGERANT (VAPOR
STATE)
Use the suction service valve on the compressor
to add a small quantity of refrigerant to the
system. Backseat the valve and connect a
charging line from the refrigerant cylinder to the
valve. Tighten connection at level of refrigerant
cylinder and open tank end slightly to purge air
from the charging line. Tighten the charging line
at the compressor. Screw in the stem of suction
valve approximately two turns. Start the engine
and run at fast idle. Add sufficient refrigerant to
bring the level in lower sight glass of receiver
tank to mid-point. Always charge the system
with the cylinder upright and the valve on top to
avoid drawing liquid out of the cylinder.
8.5 EVACUATING SYSTEM
1. Open both receiver valves by turning “out”
(normal position).
2. Remove the caps from the two 90° adapters
on the suction, discharge valves and
connect two hoses to the vacuum.
3. Place the two compressor valves, suction
and discharge, in neutral position by turning
each one 3 to 4 turns “in” from the “out”
position.
4. Open the solenoid valve by energizing or
manually bypass.
5. Start the vacuum pump. Open the large
(suction) shutoff valve and close the small
vacuum gauge valve.
6. The pressure will drop to approximately 29
inches vacuum (14.2 psi or 97,9 kPa) (the
dial gauge only gives a general idea of the
absolute system pressure.
7. Backseat the compressor valves by turning
“out” all the way.
8. Shut down the vacuum pump.
9. Remove the hoses.
10. Reinstall the caps at the suction valve take-
off points.
8.5.1 Double Sweep Evacuation Procedure
1. Remove any remaining refrigerant from the
system using a refrigerant recovery
machine.
2. Connect the evacuation manifold, vacuum
pump, hoses and micron gauge to the unit.
3. With the unit service valves closed (back
seated) and the vacuum pump and the
thermistor valves open, start the pump and
draw the manifold and hoses into a very
deep vacuum. Shut the vacuum pump off
and see if the vacuum holds. This is to
check the setup for leaks.
4. Midseat the system service valves.
5. Open the vacuum pump and the thermistor
valves. Start the pump and evacuate to a
system pressure of 2000 microns.
6. Close the vacuum pump and the thermistor
valves, turn off the vacuum pump (closing
the thermistor valve protect the valve from
damage).
7. Break the vacuum with clean refrigerant (or
dry nitrogen) and raise the pressure to
approximately 2 PSIG. Monitor the pressure
with the compound gauge.
8. Remove the refrigerant with the recovery
machine.
9. Repeat steps #5 – 8 one time.
10. After the second “sweep”, change the filter
drier (if you have not done so) and
evacuate to 500 microns.
11. Evacuating the system below 500 microns
on systems using the Carrier 05G
compressor may risk drawing air into the
system past the carbon shaft seal.
12. Check to insure that vacuum holds. (If the
pressure continues to rise, it indicates a
leak or moisture in the system).
13. Charge the system with the proper amount
of refrigerant using recommended charging
procedures.
NOTE
This method will aid in preventing
unnecessary system failures by ensuring that
the refrigeration system is free of
contaminants.