46
Marvair MAA/MGA Wall Mount AC Installation & Operation Manual
05/2023 Rev.21
C. Unit cycles on high/low pressure
limit.
1. Loss or restriction of airflow.
1. Check blower assembly for proper operation. Look
for airflow restrictions, e.g.. the air filter. Check blower
motor and condenser fan.
2. Restriction in refrigerant circuit.
2. Check for blockage or restriction, especially filter drier
and capillary tube assembly.
3. Refrigerant overcharge (following
field service)
3. Evacuate and recharge to factory specifications.
4. Defective pressure control.
4. Check limit cutout pressures. Control is set to actuate at
approximately 60 PSIG (low pressure) and 650 PSIG (high
pressure)
D. Unit blows fuses or trips circuit
breaker.
1. Inadequate circuit ampacity.
1. Note electrical requirements in Chapter 2 and correct
as necessary.
2. Short, loose, or improper connection
in field wiring.
2. Check field wiring for errors.
3. Internal short circuit. Loose or
improper connection(s) in unit.
3. Check wiring in unit. See wiring and schematic dia-
grams. Test components (especially the compressor)
for shorts.
4. Excessively high or low supply volt-
age or phase loss (3ø only)
4. Note voltage range limitations specific to the compres-
sor troubleshooting section.
E. Water on floor near unit.
1. Obstruction in condensate line.
1. Check for clog or restriction.
2. Obstruction or leak in condensate
pan.
2. Check pan for leak or blockage.
3. Unit is not level.
3. Level unit.
F. No space heating or reduced heating
(units equipped with resistance ele-
ments)
1. Defective heating element(s).
1. Check resistance element(s) for continuity.
2. Thermal limit open.
2. Check continuity across thermal limit switch.
3. Defective heater contactor.
3. Check relay for proper operation. Replace if defective.
5.3 Compressor
Troubleshooting
NOTE: It is important to rule out other component failures before condemning the compressor.
The following electrical tests will aid diagnosis:
1.
Start-Up Voltage
: Measure the voltage at the compressor contactor during start-up. The voltage
must exceed the minimum shown in Table 5, section 2.2, or compressor failure is likely. A low
voltage condition must be corrected.
2.
Running Amperage
: Connect a clip-on type ammeter to the (common) lead to the compressor. Turn
on the supply voltage and energize the unit. The compressor will initially draw high amperage; it
should soon drop to the RLA value or less. If the amperage stays high, check the motor winding
resistances.
NOTE:
Feel the top of the compressor to see if it has overheated. If it is hot, the internal overload
may be open. You may have to wait several hours for it to reset.
3.
Motor Winding Resistances:
Using a digital volt-ohm meter (VOM), measure the resistance across
the compressor windings as shown below.
C
S
R
R
2
R
1
R
3
SINGLE
PHASE
R
3
> R
2
> R
1
R
3
= R
2
+ R
1
T
1
T
2
T
3
R
2
R
1
R
3
THREE
PHASE
R
3
= R
2
= R
1
