MAINTENANCE AND REPAIR
The occurrence of the manual reset limit control to trip is an abnormal condition. Care should be taken to determine the exact reason that the high limit control tripped. Possible problem areas could be dirty heat exchanger, blocked air inlet or outlet, fan/motor malfunction, too high operating ambient, incorrect operating voltage, or leaking heat exchanger. In the event that the heat exchanger is defective, it must be replaced.
1.The manual reset limit control is located in the heating element hazardous location enclosure on the heat exchanger which is covered by the sheet metal housing attached to the side of the unit. To gain access, remove the four sheet metal screws holding the sheet metal cover in place and unthread the cast aluminum enclosure lid. (See Figure 11.) The manual reset limit control device has a small reset button protruding from the center of its back housing. Depress this button in to reset the control. Replace the aluminum enclosure lid and sheet metal cover.
Figure 11
III. FAN MOTOR AND BLADE
1.The motor is a sealed unit that requires no lubrication. If the motor is defective, it must be replaced with an original factory supplied motor. (See renewal parts section.)
2.To replace the motor, proceed as follows:
A.Disconnect the unit from power supply.
B.(Units with motor splice box) Remove 4 bolts and cover of motor splice box (See Figure 12).
C.(Units without motor splice box) Remove 16 bolts and cover of main control enclosure.
D.Note wire connections for future reference and disconnect all wires leading to the motor. All motor wires are permanently marked according to the nameplate on the motor.
Figure 12
E.Remove 4 bolts in motor base holding it to rear cabinet shelf. See Figure 13.
F.Remove 4 screws holding fan guard to cabinet.
Figure 13
G.Unthread union at motor wiring outlet nipple connection. Carefully lift the motor, fan blade, and guard off of the cabi- net.
H.Note position of fan blade on motor shaft. Loosen the two set screws to remove the fan blade and key from shaft motor.
I.Place guard and fan blade on replacement motor shaft in same locations as original motor. Align key ways in hub and shaft. Insert key flush with fan hub and tighten the two hub set screws.
J.Feed motor wires back into conduit and reposition motor back on unit. Center fan blade in opening and rotate to be sure that it clears housing and guard.
K.Thread motor nipple connection into conduit union and tight- en (5 threads minimum). Replace bolts in motor base and reat- tach fan guard to back of housing in four places. Recheck blade rotation and tighten all hardware.
L.Trim all motor leads extending out of the conduit to 6 lengths. Strip off 3/8 of insulation at cut ends. Using the motor name- plate, previous notes, and marked wires, reconnect the motor for the unit voltage rating as indicated on the heater name- plate.
M.Check fan rotation by momentarily energizing the unit. Air must exit at cabinet front. Reverse any 2 leads at contactor or line supply disconnect to reverse rotation of three phase motor.
3.Removal of fan blade does not require that the motor wiring be disturbed. To clean, service or change the fan blade proceed as follows:
A.Remove the four carriage bolts holding the motor base in place on the cabinet platform. Mark the platform to reposition at same location.
B.Loosen the four screws on the cabinet back holding the fan guard in place.
C.Pull the motor to the rear extending the conduit connection at the electrical enclosure. Fan blade and hub set screws can now be accessed by tilting the guard rearward at top or bottom back over the motor shell.
IV. ELECTRICAL COMPONENT SERVICING
EXPLOSION/ELECTRIC SHOCK HAZARD. Disconnect all power before opening enclosure covers or servic- ing heater. Failure to comply could result in personal injury or property damage.
When provided, the following components are located in the cast aluminum hazardous location enclosure. Remove cover and retaining bolts to gain access the following items (See Figure 16):
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