Dometic Qht - Digital-Controls Troubleshooting

Digital-Controls Troubleshooting Q3 and Qht Controls for Direct Expansion Systems
20 L-2516 ENGLISH
DIGITAL-CONTROLS TROUBLESHOOTING
See also “General System Troubleshooting” on page 17.
Contact an authorized Dometic servicing dealer if the problem continues or for replacement parts.
WARNING
The control board operates at 115VAC or 230VAC. Make sure the power is off before removing the cover of the control
box.
Table 7: Digital-Controls Troubleshooting
PROBLEM POSSIBLE REASON/SOLUTION
Digital display panel is not
lit.
1. No power. Turn circuit breaker on.
2. Wrong power board. Control must be connected to a Q-Logic or U-Board. It will not
work with an SMXII Power Board. Replace with Q-Logic or U-Board.
3. Check CXP and TSEP cable and connections. Replace CXP or TSEP cables if
necessary.
4. Failed equipment. Replace control, or Q-Logic or U-Board.
Erratic temperature display. 1. Shut power to the unit off and back on.
2. Perform Restore Factory Settings.
3. Check sensor cable and connections.
4. Ensure the temperature sensor is installed properly.
5. Calibrate temperature.
6. Replace Q-Logic or U-Board.
Erratic system operation. 1. Shut power to the unit off and back on.
2. Check CXP cable and connections.
3. Checktemperature sensor, cable and connections.
4. Replace control.
5. Replace Q-Logic or U-Board.
Fan is not running or runs
continuously.
Digital control is programmed for either fan cycling with compressor or continuous
fan operation.
Change Programmable Function 7. Note: When configured for aux heat, after
a heat cycle ends the fan will stay on for 30 seconds even if the fan is set to cycled operation.
Fan is not running but the
compressor is .
Failed triac on circuit board. Send for repair or call local service technician.
Fan runs continuously
although it is set to cycle
with compressor.
Failed triac on circuit board. Send for repair or call local service technician.
No cooling or heating. 1. Digital control programmed for heat or cool only. Reprogram function 19.
2. "HI / PS" or "LO / PS" is flashing. See below.
No heat. Digital Control may be set to Cool Only, not Reverse Cycle.
Change Programmable
Function 19.
Fan coil is iced. Improper airflow. See “General System Troubleshooting” on page 17 first, before
reprogramming digital control.
Change Programmable Function 21 to increase duration of Anti-Icing Routine. If anti-icing
cycle does not melt ice, switch air conditioning unit to heat until ice melts or use hair dryer to
melt ice.
System runs continuously. Improper air sensor location. Verify air sensor location with criteria found in the control
manual. Ensure that sensor is located out of direct sunlight and away from open doors or
hatches.