Testing The User Interface And Electronic Control Board; Thermistors Description - Friedrich Kuhl KCM21A30A Service Manual

WARNING
ELECTRIC SHOCK HAZARD
Turn off electric power before service or
installation. Extreme care must be used, if it
becomes necessary to work on equipment with
power applied.
Failure to do so could result in serious injury or
death.
user interface port of the electronic control board . There should be 24VDC. (refer to Electronic Control Board
Identification, Fig 712)
4. If there is no voltage, replace the electronic control board (refer to Fig 713).
5. If 24 VDC is present replace the User Interface and/ or the ribbon cable.

Thermistors Description

The KUHL units have 4 sensors (Thermistors). Each thermistor is color coded and has a different function.
1. Indoor Coil (Yellow) - located on the evaporator coil next to the power board
2. Outdoor Coil (Blue) - located on the condenser coil.
3. Discharge Air (Black) - located on the front of the unit in the discharge air port.
4. Ambient Air (White) - located on the front of the unit in front of the air intake.
Thermistor Testing
1. Gain access to Electronic Control Board (Refer to Control Board Replacement, Fig 713)
2. Locate thermistor plug and disconnect from Control Board. (refer to Control Board Identification, Fig 712)
3 ea Screw
Control
Mounting
Panel
Figure 710 Access to SSR, Capacitor, PTCR
63
COMPONENTS TESTING
Testing the User Interface and Electronic
Control Board
If the User Interface does not turn on:
1. Make sure the unit has the proper voltage and that it is
turned on. Check power at Terminals L1 and L2. (refer to
Electronic Control Board Identification, Figure 712)
2. Disconnect the User Interface's wire harness on the
control board.
3. Using a voltmeter, check the outer pins on the
3. Check for proper resistance. (refer to Thermistor
Resistance values, Fig 711
4. If thermistor is out of tolerance, replace thermistor.
Replace Soild State Relay, Capacitor, or PTCR
Models KHL24A35A, KEL36A35A, KCL28A30,
KCL36A30A are equipped with a solid state relay to
handle the higher current demands of these units. The
relay is located on the inside of the Control Mounting
Panel in between the Control Board and Power Cord.
Models KCL36A30 and KEL36A35 are equipped with
PTCR 9 Hard Start Resistor.
1) Unplug the unit.
2) Remove wire ties as necessary for slack in electrical
wiring.
3) Remove 3 screws from Control Mounting Panel.
4) Carefully pull out panel and you will have access to
replace Capacitor, PTCR, or SSR.
5) Replace Component as necessary.
6) Ensure all electrical connections are correct.
7) Reinstall Control Mounting Panel
8) Secure wiring as neccesary.
9) Plug unit back in.
10) Test Unit to ensure problems are corrected.