Service manual

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SERVICING

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During a cooling or heat pump heating demand, 24Vac is

supplied to terminal “G” of the EBTDR to turn on the blower

motor. The EBTDR initiates a 7 second delay on and then

energizes it’s onboard relay. The relay on the EBTDR board

closes it’s normally open contacts and supplies power to the

blower motor. When the “G” input is removed, the EBTDR

initiates a 65 second delay off. When the 65 seconds delay

expires the onboard relay is de-energized and it’s contacts

open and remove power from the blower motor.

During an electric heat only demand, “W1” is energized but

“G” is not. The blower motor is connected to the normally

closed contacts of the relay on the EBTDR board. The other

side of this set of contacts is connected to the heat sequencer

on the heater assembly that provides power to the first heater

element. When “W1” is energized, the sequencer will close

it’s contacts within 10 to 20 seconds to supply power to the

first heater element and to the blower motor through the

normally closed contacts on the relay on the EBTDR. When

the “W1” demand is removed, the sequencer opens it

contacts within 30 to 70 seconds and removes power from

the heater element and the blower motor.

The EBTDR also contains a speedup terminal to reduce the

delays during troubleshooting of the unit. When this terminal

is shorted to the common terminal, “C”, on the EBTDR board,

the delay ON time is reduced to 3 seconds and the delay OFF

time is reduced to 5 second.

Two additional terminals, M1 and M2, are on the EBTDR

board. These terminals are used to connect the unused leads

from the blower motor and have no affect on the board’s

operation.

S-40A AVPTC/MBVC ELECTRONIC BLOWER/

HEATER CONTROL

Description

The AVPTC and 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, heat pump, and

electric heat airflow are fully integrated into the control.

Dehumidification is enabled/disabled via an on-board

dipswitch.

Features

The new air handler control includes advanced diagnostic

features with fault recall, estimated CFM display via on-board

LED, and ComfortNet

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 AVPTC/MBVC air handlers may be used in a fully

communicating ComfortNet system when matched with a

compatiable outdoor unit and the CTK0* thermostat. A fully

communicating system offers advanced setup and diagnos-

tic features.

Basic Operation

The air handler control receives thermostat inputs either from

a standard 24VAC thermostat or the CTK0* ComfortNet

thermostat. For cooling and heat pump operation, 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

HIGH VOLTAGE!

Disconnect ALL power before servicing

or installing. 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

between 9 and 15 VDC. Replace control if voltage is not

as specified.

Electric Heat Sequencer Outputs