Thermostats (Defrost) - Friedrich WallMaster WS07A10D Service Manual

THERMOSTAT - Models ES, YS, EM, YM, EL, YL
(See Figure 29)
A cross ambient thermostat is used on all heat pump and
electric heat units. In addition to cycling the unit in a heating
or cooling operation, the thermostat will terminate the cooling
cycle in the event ice forms on the evaporator coil, in this
case the thermostat functions as a de-ice control. A resistor
(anticipator) is positioned within a plastic block to supply a
small amount of heat to the bulb area to prevent long "off
cycles" in the "Cool-Fan Auto" (MoneySaver) position (see
Figure 8.) A current feedback through the fan motor windings
during "off cycle" completes the circuit to the resistor.
In the heating cycle, the heat anticipator is energized to supply
a small amount of heat during the "on" cycle. This will open
the contacts in the thermostat prematurely to maintain a closer
differential between the "cut in" and "cut out" temperature.
The heat anticipator is energized in the heating mode
regardless of whether fan is placed in the automatic
(MoneySaver) or constant run position.
RANGE: Cooling Model Thermostat
60°F (±2°) to 92°F (±4°),
TEST:
Cooling/Heating Models: Remove wires from thermostat
and check continuity between terminal "2" (common) and "3"
for cooling. Check between terminals "2" (common) and "1"
for heating. Also check that contacts in thermostat open after
placing in either position. NOTE: Temperature must be within
range listed to check thermostat. Refer to the troubleshooting
section in this manual for additional information on thermostat
testing.
THERMOSTAT ADJUSTMENT
No attempt should be made to adjust thermostat. Due to the
sensitivity of the internal mechanism and the sophisticated
equipment required to check the calibration, it is suggested
that the thermostat be replaced rather than calibrated.
Thermostat bulb must be straight to insure proper
performance.
THERMOSTAT BULB LOCATION
The position of the bulb is important in order for the thermostat
to function properly. The bulb of the thermostat should be
located approximately 45° to a maximum of 60° from
horizontal. Also, do not allow the thermostat bulb to touch
the evaporator coil. (See Figures 30 and 31.)
THERMOSTAT BULB LOCATION
Figure 30
THERMOSTAT BULB LOCATION
Figure 31
("KQ", "YQ" and "SC" Models Only)
DEFROST THERMOSTAT
(Heat Pump Models Only)
(See Figure 32)
This thermostat is single pole - double throw with contacts
between terminals "2" and "3" closing on temperature rise
and contacts between terminals "2" and "1" closing on
temperature fall. When the contacts between terminals "2"
and "1" make, power is supplied to the heater element.
This control is dual purpose control that acts as an outdoor
thermostat and defrost control.
When the sensing bulb, attached to the condenser coil, senses
enough icing on the outdoor coil, it will interrupt power to the
compressor and supply power to the heating element until
the coil temperature reaches above 43°, then the heater will
shut off and the unit will resume operating in the reverse cycle
mode.
When the outdoor coil temperature drops below 20°, the unit
will operate in electric heat mode continuously until the outdoor
coil temperature rises above 43°.
The fan motor will not turn off when defrost occurs, and the 4-
way valve will not reverse.
("SQ" Models Only)
Thermostat sensor holder 020 and
anticipator (4712D-140) to be positioned
between the 4th and 5th and 6th and 7th
rows of tubes from the
bottom of the coil at
dimension shown
Thermostat sensor holder 020 to be
positioned between the 4th and 5th and
6th and 7th rows of tubes from the bottom
of the coil at dimension shown
35