SERVICING
24
S-40A MBVC**00AA-1 HEATER CONTROL
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, reversing
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 thermostat. Diagnostics includes heater kit selec-
tion 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 sin-
gle red LED. The estimated CFM is displayed on an on-board
green LED. The LED flashes once for each 100 CFM.
The MBVC air handlers may be used in a fully communicat-
ing system when matched with a compatible outdoor unit
and the thermostat. A fully communicating system offers ad
-
vanced setup and diagnostic features.
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.
Troubleshooting
Motor Control Circuits
WARNING
HIGH VOLTAGE
DISCONNECT ALL POWER BEFORE SERVICING OR
INSTALLING THIS UNIT. MULTIPLE POWER SOURCES
MAY BE PRESENT. FAILURE TO DO SO MAY CAUSE
PROPERTY DAMAGE, PERSONAL INJURY OR DEATH.
1. Turn on power to air handler or modular.
WARNING
LINE VOLTAGE NOW PRESENT.
2. Check voltage between pins 1 and 4 at the 4-wire motor
connector on the control board. Voltage should be be-
tween 9 and 15 VDC. Replace control if voltage is not
as specified.
Electric Heat Sequencer Outputs
WARNING
HIGH VOLTAGE
DISCONNECT ALL POWER BEFORE SERVICING OR
INSTALLING THIS UNIT. MULTIPLE POWER SOURC-
ES MAY BE PRESENT. FAILURE TO DO SO MAY
CAUSE PROPERTY DAMAGE, PERSONAL INJURY
OR DEATH.
1. Turn on power to air handler or modular blower.
WARNING
LINE VOLTAGE NOW PRESENT.
2. Disconnect the 4-circuit harness connecting the control
to the electric heater kit.
3. Provide a thermostat demand for low stage auxiliary heat
(W1). Measure the voltage between pins 1 and 3 at the
on-board electric heat connector. Voltage should mea-
sure 24VAC. Replace control if no voltage is present.
NOTE
: Allow for any built-in time delays before making
voltage measurements. Any electric heater faults that are
present may prevent the heater output from energizing. Ver-
ify that no heater faults are present before making voltage
measurements.
4. Provide a thermostat demand for high stage auxiliary
heat (W1 + W2). Measure the voltage between pins 1
and 3 at the on-board electric heat connector. Measure
the voltage between pins 2 and 3 at the on-board elec-
tric heat connector. Voltage should measure 24VAC.
Replace control if no voltage is present.
Communications (Applies only to Systems with Compatible
Outdoor Unit and Thermostat)
The integrated air handler control has some on-board tools
that may be used to troubleshoot the network. These tools
are: red communications LED, green receive (Rx) LED, and
learn button. These are described below:
a. Red communications LED – Indicates the status of the
network. Refer to the Network Troubleshooting Chart for
the LED status and the corresponding potential problem.
b.
Green receive LED – Indicates network traffic. Refer to
the Network Troubleshooting Chart for the LED status
and the corresponding potential problem.
c. Learn button – Used to reset the network. Depress the
button for approximately 2 seconds to reset the network.
For detail, see NETWORK TROUBLESHOOTING section.
