Troubleshooting Defrost System
WARNING !
Failure to heed the following may result in permanent injury or death.
Heat pumps contain no
Testing Operation of Defrost Controller:
1.Disconnect power to heater and place a jumper across the electrical connections of the DTS.
2.With HEAT mode selected, restore power to heater and turn selected thermostat to highest setting (heater should restart following five (5) minute time delay).
3.Using a suitable screwdriver or additional test jumpers, short across the two “test” pins located on the defrost control board. Shorting between the test pin terminals speeds up the “ice forming” run time by a factor of 256. In other words, if the defrost controller has been
4.If defrost does not initiate using this test method, the defrost controller is suspect. However, before condemning the controller, with test underway, measure voltage across
Testing Operation of Defrost Temperature Sensor :
The Following Procedure to be Performed by Qualified HVAC Service Personnel Only
(Best Performed After Verifying Remaining Portions of Defrost System Are Functional)
1.Disconnect power to heater; remove black fan motor power wire from the fan relay terminal. Electrically isolate the removed wire and female connector using a wrap of electrical tape.
2.Attach refrigerant service manifold gages to refrigerant test ports. Attach a reliable,
3.Repeat analysis procedure per Testing Operation of Defrost Controller, except do NOT “...place a jumper across the DTS terminals.”
4.Start heater. After a period of a few minutes, because the fan is not operating, evaporator temperature should fall to a point where the DTS closes and defrost initiates.
5.To prevent compressor damage as test progresses, monitor the suction tube temperature and superheat developed; terminate test if superheat approaches “0”. The suction tube temperature should also be used as a relative guide as to the temperature seen by the DTS.
6.If DTS does not close and initiate a defrost cycle, repeat test substituting a
7.In some instances, moving the DTS to a new coil
8.Restore fan circuit wiring to normal configuration.
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