FB, FE, FF1E, FFM, FG, FH, FJ, FMA, FT, FV, FX, FY, FZ, F54, PF: Service and Maintenance Instructions
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
24
A13140
Fig. 24 – FFMA, FMA4, FMA5 (Sizes 30 & 36) Expanded View - Evaporator Parts & Drain Pan
Electric Heater Function and Troubleshooting
FB4, FE4, FE5B, FF1E, FG5, FH4, FJ4, FJ5, FT4,
FT5, FV4, FX4, FZ, PF4, PF5
IMPORTANT: 2023 model fan coils (FJ4/5, FT4/5, FE4B/FE5) are
designed to use KFFEH electric heaters, and are not compatible with
KFCEH heaters – they use different and incompatible plugs and
polarities.
This section describes KFC, and KFD series electric heaters in exclusion
of Smart Heat by examining the functional operation of these heaters.
Description of Electric Heater Components
Limit Switch
The limit switch is a temperature sensitive control whose function is to
prevent system from overheating in abnormal conditions. The
temperature settings often vary from heater to heater due to variations in
airflow patterns and element radiant heat conditions.
The devices are sized to remain on-line under heat pump conditions
(115° air off coil) and minimum CFM, but trip to prevent outlet air
conditions above 200° F or excessive component or duct temperatures.
The device itself consists of a bimetallic disc, which when overheated
”snaps through” to open a normally closed high-voltage, high-current
switch. When system temperatures cool sufficiently, the switch will
automatically reset to its closed position. Normal failure mode for this
switch is open.
If a limit switch has been determined to be defective, NEVER BYPASS
THE LIMIT SWITCH. When replacing limit switch, ensure that it is
replaced with a limit switch of identical opening temperature and closing
differential. Limit switches are typically color coded to identify their
range.
KFC and KFD Electric Heat Relay
KFC and KFD electric heater packages have relays controlling the heater
elements instead of sequencers. A small rectifier PCB is mounted to
each relay which converts the incoming 24VAC control signal to DC.
In addition to the rectifier circuit, the second and third stage relays
contain a time-on delay circuit of five seconds for second stage, and
eight seconds for third stage. When the control signal is removed from
the relays, all relays will open with no time-off delay.
Troubleshooting KFC and KFD Series Electric
Heaters
Discolored Wire Insulation at Terminal
Check quick-connect terminal at discoloration. Connection may be
loose, creating a high resistance through connection point.
Fuse Failure
1. Check for shorted wire. Replace wire. Never try to fix wire using
electrical tape.
2. Check shorted element. If element is shorted, replace heater.
No Heat
1. Check fuse for failure. If fuse has failed, refer to (Fuse Failure
on p24).
2. Check for faulty transformer. Check output voltage of transformer
secondary side R (red) and C (brown). Make sure output is between
18VAC and 30VAC. If output voltage is low and input voltage tests
normal, replace transformer.
3. Check for miswired heater plug harness.
4. Check limit switch or sequencer failure. These switches should
have failed in open position. If output voltage is zero volts, replace
switch.
5. Check heater relay and PCB. Control voltage input to PCB should
be 24VAC. Output to relay should be 18VDC minimum. If input is
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