Qmark GUX - Explosion Proof Unit Heaters - Manual (Page 8)

MAINTENANCE AND REPAIR
The occurrence of the manual reset limit control to trip is an abnor-
mal 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 mal-
function, 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 hold-
ing the sheet metal cover in place and unthread the cast alu-
minum 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.
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 perma-
nently marked according to the nameplate on the motor.
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.
G. Unthread union at motor wiring outlet nipple connection.
Carefully lift the motor, fan blade, and guard off of the cabinet.
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
tighten (5 threads minimum). Replace bolts in motor base
and reattach 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 nameplate, previous notes, and marked wires, recon-
nect the motor for the unit voltage rating as indicated on the
heater nameplate. Re-attach the ground wire to the connec-
tion inside the enclosure. Replace cover and tighten securely.
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.
8
Figure 12
Figure 13
5-3/4"
5-3/4"
Reset
Button
Figure 11