SECTION 22: HEATING AND AIR CONDITIONING
36
DOB 2490-2789 | X3-45 Commuter PA1605 Maintenance Manual (Final Version – Rev.2 April 2016)
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.
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, full
charge.
2. Install the pressure gauge at compressor
suction, but then add 3 PSI to reading.
FIGURE 46: SUPERHEAT ADJUSTMENT INSTALLATION
22046
3. Install a remote reading thermometer to the
evaporator outlet line near the existing
remote bulb (Figure 46).
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.
FIGURE 47: HIGH & LOW SWING TEMPERATURE AT
REMOTE BULB
22047
6. Check approximately 5 readings of suction
pressure at 2-minute intervals and convert
to temperature using the temperatures &
pressures table (paragraph 7.13). 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 (refer to Figure 47).
Example of readings taken:
A/C pressure gauge at
40°F
