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Air Conditioner
Component
EN
Diagnostic Question
Evaporator Blower Capacitor
Is the evaporator fan slow
or not running?
High-Pressure Switch
Is the high-pressure
switch experiencing open
conditions?
Low-Pressure Switch
Is the low-pressure switch
experiencing open
conditions?
Is the Q3 control calling?
Is there no heat or no
cooling?
Temperature Sensor 15 ft . (4 .6 m)
Is the temperature not
reading properly?
Action Based On Status
Test the mF value of the evaporator blower capacitor
for 20 mF. If the mF value is incorrect, replace the
evaporator blower capacitor.
Check for a poor connection or open wire in the wiring
to and from the capacitor.
Test the high-pressure switch
– Opens at 625 PSI ± 25
– Closes at 450 PSI ± 15. Check for continuity when
the switch is closed.
Check the condenser airflow and remove any
obstructions as necessary.
Check the condenser fan operation.
If the switch proves faulty, replace the high-pressure
switch.
Check the refrigerant system pressure to ensure the
system is not out of refrigerant.
Test the low-pressure switch:
– Opens at 60 PSI ± 5
– Closes at 75 PSI ± 5. Check for continuity when the
switch is closed.
If the switch proves faulty, replace the low-pressure
switch.
Q3 Control
Check the illumination of the Q3 control. If it is not
working, substitute a known good Q3 control unit and
retest.
Check the Q3 control set point is set properly based
on the inside temperature:
– Press and release the Up or Down button on the
QC Control to view the current Q3 control set
point.
– Raise or lower the set point as necessary.
Check that the correct heating or cooling mode is
active on the Q3 control. If not, set the correct mode.
• Check continuity. The reading should be
approximately 3,000 Ohms at 77 °F (25 °C).
• Confirm the latch is in place.
• Check contacts for moisture or corrosion on
connectors. If sensor is suspect, substitute a known
good sensor and retest.
• Check for damage. Replace the sensor if it is
damaged. Remove the sensor by unplugging it.
Re-insert the sensor by plugging the ends into the
appropriate plug-in.
Check the temperature against a known good
thermometer and calibrate the sensor, if necessary.
Diagnostic Procedures
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