Checking Temperature Rise; Testing Primary Limit Control - Daikin APGM3 Service And Troubleshooting

SERVICING

Checking Temperature Rise

Temperature rise is related to the BTUH output of the
unit and the amount of air (CFM) circulated over the heat
exchanger.
All units are designed for a given range of temperature
increase. This is the temperature of the air leaving the unit
minus the temperature of the air entering the unit.
The more air (CFM) being delivered through a given
unit the less the rise will be; so the less air (CFM) being
delivered, the greater the rise. The temperature rise should
be adjusted in accordance to a given unit specifications
and its external static pressure.
1. Check BTUH input to unit do not exceed input rating
stamped on rating plate.
2. Take entering and leaving air temperatures.
3. Select the proper speed tap or dip switch setting for
direct drive units.
4. Take motor amperage draw to determine that the
motor is not overloaded during adjustments.
SUPPLY
T
SUPPLY
T
RETURN
Checking Temperature Rise

Testing Primary Limit Control

APG/GPG units use a snap-disk type primary limit device.
Sometimes referred to as "stat on a stick". The limit setting
is fixed and must not be readjusted in the field.
Testing Primary Limit Control
Refer to the specification section to determine the proper
limit cutout temperature for the model being serviced.
In all instances the limit control is wired in series with the
ignition control.
If the temperature within the furnace should exceed this
setting, the control will open, de-energizing the ignition
control which in turn will open the electrical circuit to the
gas valve.
The control will automatically reset when the temperature
within the combustion chamber is sufficiently lowered.
RETURN
T T
RISE = SUPPLY - RETURN
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