Dometic Qht - Page 20

General System Troubleshooting Q3 and Qht Controls for Direct Expansion Systems
18 L-2516 ENGLISH
Low airflow. 1. Airflow is blocked. Remove any obstructions in return-air stream. Clean return-air
filter and grille. Check for crushed or restricted ducting; ducting must be as straight,
smooth and taut as possible.
2. Fan Coil is iced. See below.
3. Fan speed is set to manual low. If the fan speed is set to manual low, press and
release the Fan button until the desired fan speed and airflow are reached. If you
want automatic fan speed control, press and release the Fan button until the letter “A”
displays.
Fan is not running.
Check “Digital-Controls Troubleshooting” on page 20.
No cooling or heating. 1. Temperature set point is satisfied. Lower or raise set point.
2. Obstructed seawater flow. Clean seawater strainer. Check for obstructions at speed
scoop thru-hull inlet. Check for a good steady flow from the overboard discharge.
3. Seawater pump may be air-locked. Remove hose from pump discharge to purge air
from line.
4. Loss of refrigerant gas. Check air conditioning unit for refrigerant oil leakage, call
service technician.
5. Seawater temperature too high for cooling or too low for heating. Seawater
temperature will directly affect air conditioning unit’s efficiency. This air conditioning
unit can effectively cool your boat in water temperature up to 90°F (32.2°C) and heat
(if reverse-cycle option is installed) in water temperatures as low as 40°F (4.4°C).
6. Fan coil is iced (in cooling). Check your specific control troubleshooting section.
7. Fan is not running. Check your specific control troubleshooting section.
8. Control is in fan-only mode. Set system for Cool Mode or Heat Mode.
9. Seawater plumbing is air-locked. Ensure that seawater plumbing is installed per the
guidelines in this manual.
10. Digital control is programmed for Cool or Heat only. See “Digital-Controls
Troubleshooting” on page 20.
11. High-pressure switch is open (in cooling) due to improper seawater flow.
Strainer or intake may be plugged, seacock may be closed, check seawater hose for
kinks or collapses. Verify pump operation. Check pump circuit breaker if applicable.
12. High-pressure switch is open (in heating) due to improper airflow. Remove any
obstructions in return air stream. Clean return air filter and grille. Check for crushed or
restricted ducting, ducting must be as straight, smooth and taut as possible.
13. High-pressure switch is open (in heating) due to high seawater temperature.
System may cycle on high pressure if seawater temperature is above 55°F (12.8°C).
14. Compressor’s thermal overload is open due to either of the above reasons.
Compressor needs to cool down. Turn system off for a while (it may take up to three
hours to reset thermal overload).
No heating. Unit is in cool-only mode, or if reverse cycle, reversing valve may be stuck.
Tap
reversing valve lightly with rubber mallet while unit is in heat mode. Call for service if that does
not correct the problem.
Table 6: General System Troubleshooting (continued)
PROBLEM POSSIBLE REASON/SOLUTION