Friedrich WallMaster 2009 Service Manual page 39

Problem
Heat anticipator (resistor) shorted
(on applicable models)
Room
Wide differential - partial loss of
temperature
t-stat bulb charge
uneven
(Heating cycle)
Incorrect wiring
Defective thermistor or control board Replace thermistor or electronic control board
Problem
Incorrect wiring
Defrost control out of calibration
(applicable models)
Unit will not
Defrost control contacts stuck
defrost
Defrost control bulb removed from
or not making good coil contact
Outdoor coil thermistor
Problem
Dirty fi lter
Unit undersized
Outdoor t-stat open (applicable
Does not heat
models)
adequately
Heater hi-limit control cycling on &
off
Shorted supplementary heater
Incorrect wiring
Defective thermistor or electronic
control board
HEAT PUMP TROUBlESHOOTING
Possible Cause
Possible Cause
Possible Cause
Action
Disconnect power to unit. Remove resistor
from t-stat bulb block. Plus in unit & allow to
operate. Feel resistor for heat. If not heat,
replace resistor
Replace t-stat & check
Refer to appropriate wiring diagram. Resistor
is energized during "ON" cycle of compressor
or fan.
Action
Refer to appropriate wiring diagram
If outside coil temperature is 25°F or below,
& preselected time limit has elapsed, replace
defrost control
If contacts remain closed between terminals
"2" & "3" of the defrost control after
preselected time interval has passed, replace
control
Reinstall & be assured that good bulb to coil
contact is made
Replace thermistor or electronic control board
Action
Clean as recommended in Owner's Manual
Check heat rise across coil. If unit operates
effi ciently, check if insulation can be added
to attic or walls. If insulation is adequate,
recommend additional unit or larger one
T-stat should close at 38°F. Check continuity
of control. If temperature is below 38°F,
replace control
Check for adequate fan air across heater.
Check control for open at 160°F & close at
150°F
Ohmmeter check, approx. 32-35 ohms
Check applicable wiring diagram
Replace thermistor or electronic control board
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