Compressor Overload Fault (Ft 20)
The Chiller has both low and high refrigerant pressure sensors. They are wired in series and connect to DAF2
on the Control PCB. If either sensor opens, the Ft 20 alarm is activated. To troubleshoot, measure the continuity
across each senor.
Low Pressure Sensor
The low pressure sensor opens if the suction pressure drops below 15 psi (1 bar) and automatically closes
when the suction pressure rises above 30 psi (2.1) bar. If a continuity check of this sensor shows that it is open,
it is probably due to a loss of refrigerant, although a faulty sensor cannot be ruled out. Contact your local HVAC
technician to check the refrigeration system.
High Pressure Sensor
The high pressure sensor opens if the discharge pressure exceeds 630 psi (43.4 bar). If a continuity check
shows that this sensor is open, it may be due to high ambient temperature, dirty air filters, or large heat loads. A
faulty sensor cannot be ruled out.
Once the high pressure sensor opens, it must be manually reset as follows:
WARNING: Compressor and copper tubing may be very hot.
1. Remove the front right side panel of the Chiller housing.
2. Locate the blue sensor with red reset button on the compressor discharge line.
3. Depress the red reset button.
4. Replace front right side panel.
If high ambient temperature, dirty air filters, or large heat loads have been ruled out as reasons for an open high
pressure sensor and the sensor remains open or continues to open, contact your local HVAC technician to
check the refrigeration system.
110-279 37
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