T -295
4-7
4.13 EVAPORATOR COIL REPLACEMENT
a. If refrigerant remains in the system, perform a low
sidepump down to removerefrigerantfromtheevap-
orator coils.
CAUTION
If unit was recently operated, be careful of
remaining hot coolantin thehoses whendis-
assembling.
b. Remove fresh air i ntake.
c. Drain heater coil by removing the required coolant
from t he engine cooling system.
d. Remove 12 mounting screws, 4 each at the receiver
support, at the front of the unit and at the return air
opening.
e. Remove the electronic board and harness.
f. Remove the filter--drier.
g. Disconnect suction line hose and lift coil out of unit.
h. To install the coil assembly, reverse the removal pro-
cedure.
4.14 SERVICING THE HEAT VALVE
The heat valve (Figure 4-9) requires no maintenance
unless a malfunction to the internal parts or coil occurs.
This may be caused by foreign material such as: dirt,
scale, or sludge in the coolant system, or improper
voltage to the coil.
There are only three possible valve malfunctions: coil
burnout, failure to open, or failure to close.
Coil burnout may be caused by the following:
1 Improper voltage.
2 Continuous over-voltage, more than 10% or Under-
voltage of more than 15%.
3. Incomplete magnetic circuit due to the omission of
the coil housing or plunger.
4. Mechanical interference with movement of plunger
which may be caused by a deformed enclosing tube.
Failure to open may be caused by the following:
1 Coilburnedoutor anopencircuit to coilconnections.
2 Improper voltage.
3 Torn diaphragm.
4 Defective plunger or deformed valve body assembly.
Failure to close may be caused by the following:
1 Defective plunger or deformed valve body assem-
bly.
2 Foreign material in the valve.
3 Torn diaphragm.
4.14.1 Coil Replacement
a. It is not necessary to drain the coolant from the sys-
tem.
b. Placemainbatterydisconnect switchin OFFposition
and lock.
c. Disconnect wire leads to coil.
d. Remove coil retaining screw and nameplate.
e. Li ft burned-out coil fr om enclos in g t ube and replace.
f. Connect wire leads and test operation.
4.14.2 Internal Part Replacement
a. Placemainbatterydisconnect switchin OFFposition
and lock.
b. Open the vent fitting at the top of the outlet header of
the heater coil.
c. Draincoilbyopeningthedrain-cockon theinlettube.
d. Disassemble valve and replace defective parts.
e. Assemble valve, refill and bleed coolant lines.
4.14.3 Replace Entire Valve
a. Placemainbatterydisconnect switchin OFFposition
and lock.
b. Drain coolant from lines as previously described and
disconnect hoses to valve .
c. Disconnect wire leads to coil.
d. Remove valve assembly from bracket.
e. Install new valve and re-connect hoses. It is not ne-
cessarytodisassemblethevalvewheninstalling.
f. Refill and bleed coolant lines.
g. Connect wire leads and test operation.
1
2
3
4
5
6
7
8
9
10
1. Coil Retaining Screw
2. Nameplate
3. Coil Housing
Assembly
4. Enclosing Tube &
Bonnet Assembly
5. Kick-Off Spring
6. Plunger
7. Closing Spring
8. Diaphragm
9. O-Ring
10. Valve Body
Figure 4-9. Heat Valve
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