Testing Eev Coil Resistance; Testing Reversing Valve; Mbvc**00Aa-1 Heater Control - Maytag Amana VZC20 Service And Troubleshooting

SERVICING

TESTING EEV COIL RESISTANCE

To check the resistance of the EEV coil, first disconnect
EEV cable from the Control board. Make measurements of
resistance between the connector pins, and then make sure
the resistance falls in the range of 40 to 50Ω.
Outdoor unit: 3. 4. & 5 Ton

TESTING REVERSING VALVE

CHECKING REVERSING VALVE AND SOLENOID
Reversing valve used in heat pumps could potentially leak
internally. Discharge gases can leak into the suction inside
the valve. Compound gages will give the same symptoms
as bad compressor valves or broken scroll flanks. The
temperature between true suction and the suction line after
the valve should not be greater than 4 degrees. Note: The
center tube is always the suction line and should be cold.
TROUBLESHOOTING THE REVERSING VALVE FOR
ELECTRICAL FAILURE
Place unit into the cooling mode. Test for 24 volts at the
solenoid. If there is no voltage present at coil, check the
control voltage. If voltage is present, loosen the nut on the
top of the coil. Remove the coil, there should be slight resis-
tance. If the slight resistance is felt, remove the coil. As you
remove the coil listen carefully, an audible click should be
detected. The clicking is due to the movement of the pilot
valve plunger. The absence of a clicking sound indicates
the plunger is stuck.
TROUBLESHOOTING MECHANICAL FAILURES ON A
REVERSING VALVE BY PRESSURE
Troubleshooting the reversing valve can be done by pres-
sure and touch. Raise the head pressure. In the cooling
mode block the fan exhaust. Once head pressure has been
raised, cycle between cooling and heating and see if the
piston can be freed.
TROUBLESHOOTING MECHANICAL FAILURES ON A
REVERSING VALVE BY TEMPERATURE
When operating properly the valve contains refrigerant
gases at certain temperatures. The discharge line should be
the same temperature after the valves discharge line.
The true suction should be the same as the suction line
after the valve. If there is a 4-degree difference, valve is
18
Outdoor unit: 2 Ton
leaking. When stuck in the mid-position, part of the dis-
charge gas from the compressor is directed back to the
suction side, resulting in excessively high suction pressure.
An increase in the suction line temperature through the
reversing valve can also be measured. Check operation of
the valve by starting the system and switching the opera-
tion from COOLING to HEATING cycle. If the valve fails to
change its position, test the voltage (24V) at the valve coil
terminals (X25A) on outdoor unit PCB while the system is
on the COOLING cycle. If voltage is registered at the coil,
tap the valve body lightly while switching the system from
HEATING to COOLING, etc. If this fails to cause the valve
to switch positions, remove the coil connector cap and test
the continuity of the reversing valve solenoid coil. If the coil
does not test continuous - replace it. If the coil test continu-
ous and 24 volts is present at the coil terminals, the valve is
inoperative - replace it.
MBVC**00AA-1 HEATER CONTROL (OPTIONAL)
DESCRIPTION
The MBVC models utilize an electronic control that provides
ECM blower motor control and control of up to two electric
heat sequencers. The control has thermostat inputs for up
to two stages of cooling, two stages of electric heat, revers-
ing valve, and dehumidification. Control input is 24VAC.
All dipswitches necessary to setup cooling and electric heat
airflow are fully integrated into the control.
FEATURES
The new air handler control includes advanced diagnostic
features with fault recall, estimated CFM display via on-
board LED, and ComfortNetTM ready. Diagnostics includes
heater kit selection diagnostics, open fuse, internal control
fault, data errors, and blower motor faults. Data errors are
not included in the fault recall list. Diagnostic error codes
are displayed on a single red LED.
The estimated CFM is displayed on an on-board green
LED. The LED flashes once for each 100 CFM.
The AVPEC air handlers may be used in a fully communi-
cating ComfortNet system when matched with a compatible
outdoor unit and the CTK04 thermostat. A fully communi-
cating system offers advanced setup and diagnostic fea-
tures.
BASIC OPERATION
The air handler control receives thermostat inputs from the
CTK04 ComfortNet thermostat. The control operates the
variable speed blower motor at the demand as determined
from the thermostat input(s). If a demand for electric heat
is received, the control will provide a 24VAC output for up to
two electric heat sequencers.