Carrier PrimeLINE 69NT40-561-200 Operation And Service Manual page 136

e. At the load side of the heater contactor, check the insulation resistance to ground.
If readings are > 1 Mohm, then the heaters are operating properly and no action is needed.
If readings are < 1 Mohm, then the faulty heater needs to be identified. Proceed to step 3 for units
with a heater access panel or step 4 for units without a heater access panel.
3. Identify the faulty heater(s) for units with a heater access panel:
a. Open the access panel and cut out all wire splices to isolate all heaters inside of the unit.
b. Repeat the Megger test on each individual heater. Connect the ground clip to the outer metal sheath of
the heater and the test clip to one of the wires from the same heater.
c. Replace any heater where the readings are < 1 Mohm.
4. Identify the faulty heater(s) for units without a heater access panel:
a. Remove all six connections from the Heater (HR) contactor load side, which splits the six heaters into
three separate pairs.
b. Identify the following three wires: DHTL, DHML, DHBL. There is one from each load connection.
c. Repeat the Megger test on each pair of heaters to identify the faulty heater pair. Connect the ground clip
from the insulation tester to a fixed ground point on the unit, preferably the ground plate in the control
box. Connect the test clip to one of the wires stated above.
d. Test all three wires and replace any heater pair that has readings < 1 Mohm.
5. If the unit is loaded, and the heater can not be immediately replaced, perform the following steps:
a. Identify the wire at the opposite end of the faulty heater pair: DHTL - DHTR, DHML - DHMR, DHBL -
DHBR.
b. Isolate the two wires.
c. Reconnect the remaining good wiring pairs to their original connections.
d. The unit will fail the PTI test P1-0 at the next pre-trip inspection. Repair action can be taken at that time.
6. If the unit is empty, replace the faulty heater:
Before servicing the unit, make sure the circuit breakers (CB-1 & CB-2) and start-stop switch
(ST) are in the OFF position and the power plug is disconnected.
a. With the heater pair identified, remove the upper back panel inside the container.
b. Identify the center point connection for the heater pair (black wiring from heaters) either against the unit
back wall or in the wiring loom.
c. Cut the splice to separate the two heaters.
d. Carry out a Megger check on the two heaters in the same way as for units with heater panel. Replace
any heater where the Megger readings are < 1 Mohms.
If all heaters are above the acceptable limit with the wiring disconnected, then this indicates that the
fault was in one or more of the wire splices that were removed.
e. Remove the hold-down clamp securing the heater(s) to the coil.
f. Verify that the heaters are not hot before handling them.
g. Lift the bent end of the heater (with the opposite end down and away from the coil). Move the heater to
the side enough to clear the heater end support and remove.
h. To install heater, reverse steps.
T-362
WARNING
!
NOTE
7–18