PREVOST X3-45 COMMUTER User Manual

SECTION 22: HEATING AND AIR CONDITIONING
DOB 1300-1556 | X3-45 Commuter PA-1648 Maintenance Manual First release Oct 2020
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pin to full open position, is of vital importance
because it provides savings in both initial
evaporator cost of operation.
Accurate and sensitive control of the refrigerant
liquid flowing to the evaporator is necessary to
provide maximum evaporator capacity under
load conditions. The spring is adjusted to give
12 to 16
o
F (-11.1 to -8.8
o
C) of superheat at the
evaporator outlet.
This ensures that the refrigerant leaving the
evaporator is in a completely gaseous state
when drawn into the suction side of the
compressor. Liquid would damage the
compressor valve, piston and heads if allowed to
return in the suction line.
A vapor is said to be superheated when its
temperature is higher than the saturation
temperature corresponding to its pressure. The
amount of the superheat is, of course, the
temperature increase above the saturation
temperature at the existing pressure.
As the refrigerant moves along in the
evaporator, the liquid boils off into a vapor and
the amount of liquid decreases until all the liquid
has evaporated due to the absorption of a
quantity of heat from the surrounding
atmosphere equal to the latent heat of
vaporization of the refrigerant. The gas
continues along in the evaporator and remains
at the same pressure. However, its temperature
increases due to the continued absorption of
heat from the surrounding atmosphere. The
degree to which the gas refrigerant is
superheated is related to the amount of
refrigerant being fed to the evaporator and the
load to which the evaporator is exposed.
4.9.2 Superheat Adjustment
Expansion valves are factory preset for optimum
superheat settings. This setting should be
modified only if absolutely necessary. The
readjustment should be at the lowest expected
evaporating temperature.
1. Operate coach for at least one-half hour at
fast idle with temperature control set at 82
o
F
(27,7
o
C), then set temperature to minimum
to keep the compressor on 4 cylinders.
FIGURE 37: SUPERHEAT ADJUST. INSTALLATION 22046
2. In the DID “Gages” Menu note the indicated
“LoS” (Low side) pressure.
3. Use a remote reading thermometer or
thermocouple / multimeter to measure
temperature at the evaporator outlet line
near the existing remote bulb (Figure 37).
4. Apply thermostatic tape around the bulb
and evaporator outlet line to get a true
reading of the line temperature.
5. Block condenser if necessary to keep
pressure over 150 psi.
6. Check approximately 5 readings of pressure
at 2-minute intervals and convert to
temperature using the vapor-pressure table.
Likewise check the temperature reading at
the remote bulb at the same 2-minute
intervals and record the low and high swing
readings of the needle (Figure 38).
FIGURE 38: HIGH & LOW SWING TEMPERATURE AT
REMOTE BULB
22047

PREVOST X3-45 COMMUTER Specifications

General

Engine	Volvo D13
Transmission	Allison B500
Fuel Type	Diesel
Length	45 ft (13.7 m)
Width	102 in (2.6 m)
Horsepower	500 hp
GVWR	54, 000 lbs
Height	141 in