P9 Test - DTT Close and Open Test:
The DTT in this control is not a physical device, with actual metallic
contacts, it is a software function that acts similar to a thermostat.
Using various temperature inputs, the DTT function determines whether a
thermostat mounted on the Evaporator Coil would have OPEN or CLOSED
contacts. Primarily, the DTT function operates based on the temperature
reading from the Defrost Termination Sensor.
| P9-0 DTT Closed and Open Test |
| During P9-0 the defrost temperature sensor (DTS) reading will be displayed on the left display. The right display will show the supply air temperature. The unit will run FULL COOL for 30 minutes maximum until the DTT is considered closed. This step may not have to be executed. Once the DTT is considered closed, the unit simulates defrost by running the heaters for up to two hours, or until the DTT is considered open. Test fails if: The DTT is not considered closed after the 30 minutes of full cooling HTT opens when DTT is considered closed or if return air temperature rises above 248 C (120 F). Test passes if the DTT is considered open within the 2 hour heat cycle time limit. |
