Defrost Control

Single-Zone and Dual-Zone Sequence of Operation

Testing Defrost Operation using test pins

DFT TST

R and DF2

Warning!

Before removing the access panels to the unit make sure that all power is dis- connected from the unit. Failure to do so could result in injury or electric shock.

Defrost operation can be initiated us- ing the test pins located on the circuit board of the condensing unit. “Defrost test operation” will be a time compressed ver- sion of the actual defrost cycle.

With the system “off”, using two small alligator clips, jumper the following sets of test pins. “R and DF2” and “DFT TST”.

Defrost control board: Apply power to the indoor and outdoor units. Place the indoor unit in heating mode with the set point temperature well above room tem- perature. This is to ensure that the con- denser will remain on during the entire defrost test operation.

The condenser will operate in heat- ing for approximately 20 seconds. At that point the unit will enter defrost mode for approximately 2 seconds. During this time the condenser fan will switch off, the re- versing valve will energize and the defrost board will energize the indoor electric heat relay through the “W” terminal. After

the two second defrost cycle is complete, the unit will switch back to heating opera- tion for another 20 seconds. This process will repeat until the jumpers are removed from the test pins.

Note: If the condenser coil is heavily frosted up with ice, it is likely that the “Defrost Sensor” is already closed. In this case the “R and DFT” jumper can be eliminated. To initiate defrost, mo- mentarily jump pins marked “DFT TST” until the defrost cycle begins. The unit will remain in defrost mode until the condenser coil is defrosted and then it will return to heating mode. When test- ing is complete be sure to remove the jumper(s). DO NOT leave the unit in test mode with jumper(s) in place.

Defrost controls with short cycle protection (heat pumps only): The unit is equipped with a logic control circuit de- signed to keep system operating at peek efficiency. The 24v circuit provides control to the indoor and outdoor systems includ- ing a three minute, anti-short cycle timer (ASCT) compressor protection.

The defrost control circuit is designed to keep the condenser coil free from frost and ice during heating mode. This is ac- complished through the precise switching sequence of the outdoor fan, reversing valve and indoor auxiliary heater.

Defrost initiation: The defrost-sensor is located on either the end plate or the re- turn bend of the condenser coil. A defrost cycle will initiate after the sensor closes (approx. 30° F) and remains closed for the length of time selected on the control board (either 30, 60 or 90 minutes)*.

At the start of the defrost cycle, the re- versing valve will change from heating to cooling mode. The condenser fan will also switch off, there-by allowing pressure and temperature to rise within the condenser

Multi-zone Heat Pump Condensing Units

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