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4.15.2 Cold (Freeze) Control
Blue Two Pin Plug
The cold (freeze) control is used on both air conditioners
and heat pumps. When the temperature of the coil reach-
es the freezing point the compressor will stop operation
and the fan will automatically go to high speed. The cold
control is a thermistor and senses the coil temperature.
Unplug the sensor (blue plug) from the AC power module
board. Using an ohmmeter, check the ohms through the
freeze sensor on the wire side of the plug. When check-
ing the sensor go from each wire at 2 pin plug to chas-
sis ground. If one of the wires is partially grounded it will
give the control board a false reading. Check the ohms
through the sensor and compare it to the chart. Any varia-
tion requires the sensor to be replaced.
4.15.3 Ambient Sensor
Red Two Pin Plug
The ambient sensor is the outside air temperature sen-
sor and used on Comfort Control heat pumps only. This
device allows the heat pump to operate down to approxi-
mately 32° F. To check the ambient sensor, rst measure
the outside temperature near the sensor. Unplug the sen-
sor (red plug) from the AC power module board. Using
an ohmmeter, check the ohms through the ambient sen-
sor on the wire side of the plug. The temperature reading
taken near the ambient sensor should correspond to the
readings on the chart. When checking the sensor go from
each wire at 2 pin plug to chassis ground. If one of the
wires is partially grounded it will give the control board a
false reading.
4.16 Analog Cold Control
The cold (freeze) control is used on roof top air condition-
ers ONLY. If used with roof top heat pumps it can cause
premature shut off of the compressor. The cold control is
normally open (no continuity), and closed when the tem-
perature is below 41° F. to 49° F. The switch will return
to the open position at 61° F. to 69° F. Check continuity
through the switch, in temperatures over 69° F. it should
be open (no continuity) and in temperatures below 49° F.
it will be closed. Any variation requires the switch to be
replaced.
Center The Cold
Control Switch
On Evaporator
Coil
Cold Con-
trol Switch
Below Heat
Strip
Drain Pan
Evaporator
Coil 2nd Tube
From Coil
Bottom
Snap Cold Control Switch On 2nd
Tube From Bottom
579
591 & 595
Series Units
600
620 & 630
Series Units
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