Superheat Adjustment - PREVOST H3-41 Maintenance Manual

SECTION 22: HEATING AND AIR CONDITIONING
the superheat necessary to open the valve. It is
obvious, then, that it is most important to adjust
the operating superheat correctly and that a
minimum change in superheat to move the valve
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
F (-11.1 to -8.8
12 to 16
o
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
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
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
atmosphere equal to
vaporization of the
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
superheated is related to the amount of
refrigerant being fed to the evaporator and the
load to which the evaporator is exposed.
4.11.2

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
(27,7 C), Then set temperature to minimum
o
to keep the compressor on 4 cylinders.
40 PA1621 Maintenance Manual All Series | Revised February 2019
C) of superheat at the
o
would damage the
moves along in the
from the surrounding
the latent heat
refrigerant. The gas
gas refrigerant
FIGURE 57: SUPERHEAT ADJUST. INSTALLATION
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 57).
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.
of
6. Check approximately 5 readings of pressure
at 2-minute
temperature using the vapor-pressure table.
Likewise check the temperature reading at
the remote bulb at the same 2-minute
is
intervals and record the low and high swing
readings of the needle (Figure 58).
F
o
FIGURE 58: HIGH & LOW SWING TEMPERATURE AT
REMOTE BULB
intervals and convert
22047
22046
to