Maytag Amana VZC20 Service And Troubleshooting page 31

SERVICING
• Measure static pressure of the return duct at the inlet
of the furnace
• Measure the static pressure of the supply duct at the
outlet of the furnace
• NOTE: Both readings may be taken simultaneously
and read if so desired
If the total external static pressure and/or static pressure
drop exceeds the maximum or minimum allowable statics,
check for closed dampers, dirty filters, undersized or poorly
laid out duct work.
AIRFLOW CONSIDERATION
Airflow demands are managed differently in a fully commu-
nicating system than in a non-communicating wired system.
The system operating mode (as determined by the thermo-
stat) determines which unit calculates the system airflow
demand. If the indoor unit is responsible for determining the
airflow demand, it calculates the demand and sends it to the
ECM motor. If the outdoor unit or thermostat is responsible
for determining the demand, it calculates the demand and
transmits the demand along with a fan request to the indoor
unit. The indoor unit then sends the demand to the
ECM motor. The table below lists the various
communication systems, the operating mode, and airflow
demand source.
System Operating
System
Cooling
Heat Pump Heating
Any
Continuous Fan
HP + Electric Heat
Air Handler or
Modular blower
Electric Heat Strips
Gas Furnace Combustion Heat
For example, assume the system is an outdoor unit
matched with an indoor unit. With a call for cooling, the out-
door unit will calculate the system's cooling airflow demand.
The outdoor unit will then send a fan request along with the
cooling airflow demand to the indoor unit. Once received,
the indoor unit will send the cooling airflow demand to the
ECM motor. The ECM motor then delivers the cooling
airflow.
Airflow Demand
Mode Source
Outdoor Unit
Outdoor Unit
Only
Thermostat
Either outdoor unit or
indoor unit, which has
Strips
higher Airflow demand
Indoor Unit
Only
Indoor Unit
In continuous fan mode, the communicating thermostat
provides the airflow demand. The communicating provides
4 continuous fan speeds (25%, 50%, 75% and 100% of
maximum airflow). During continuous fan operation, the
thermostat sends a fan request along with the continuous
fan demand to the indoor unit. The indoor unit, in turn,
sends the demand to the ECM motor. The ECM motor deliv-
ers the requested continuous fan airflow.
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