TM9-4120-400-14
2-6. OPERATIONAL CHECKS. - continued
NOTE
For maximum ventilation with fresh air, it is necessary that room or enclosure air have a
means of exit through an open door or window. If the room or enclosure is tightly closed,
an over pressure will build up and decrease the volume of fresh air drawn in.
i. Fully open the return air louvers and fully close the fresh air damper.
j. Turn the TEMPERATURE SELECTOR (thermostat) knob to the full WARMER (clockwise) position. Then
turn-the MODE SELECTOR switch to LOW HEAT. Place your hand in the airflow from the conditioned air supply
louver and feel for a temperature rise. When the supply air temperature has reached a relatively stable level, turn
the MODE SELECTOR switch to HIGH HEAT and feel for a further temperature rise. Next, turn the
TEMPERATURE SELECTOR thermostat control knob to the fully COOLER (counterclockwise) position. Feel that
supply air temperature drops to approximately the same relatively stable level previously noted in LOW HEAT.
Finally, turn the MODE SELECTOR switch to LOW HEAT and feel the discharge air temperature drop to ambient
level (room temperature).
NOTE
The TEMPERATURE SELECTOR (thermostat) control has an effective functional range
between 60F and 90F (16C and 32C). In extreme conditions when ambient air
temperature is below 60F (16C) or above 90F (32C), the operation in either LOW
HEAT or HIGH HEAT mode will vary from that described above.
If a knocking or pounding noise is heard when the compressor starts in the following
check, immediately turn the MODE SELECTOR out of the COOL position. Leave input
power connected and wait at least two hours before attempting another start in COOL
mode.
k. Turn the TEMPERATURE SELECTOR control knob to the fully WARMER (clockwise) position, then turn
the MODE SELECTOR switch to COOL. Note that the evaporator and condenser fans start immediately and that
the compressor starts approximately 30 seconds later. Hold your hand in the airflow from the conditioned air
supply louver; there should be no change in temperature. Now turn the TEMPERATURE SELECTOR control
knob to the fully COOLER (counterclockwise) position and feel the supply air temperature begin to drop almost
immediately. Leave controls in the present position and perform the next check.
Figure 2-7. Refrigerant Sight Glass
2-9