Testing Primary Limit Control; Testing Auxiliary Limit - Daikin M Series Service And Troubleshooting

SERVICING
SUPPLY
T
SUPPLY
T
RETURN
Checking Temperature Rise

Testing Primary Limit Control

APD/GPD 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.
RETURN
T T
RISE = SUPPLY - RETURN
The control will automatically reset when the temperature
within the combustion chamber is sufficiently lowered.
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. Remove electrical power to unit. Some units may
have more than one source of power.
2. Remove the wires from the limit control terminals.
3. Using an ohmmeter, test for continuity across the two
terminals.
4. If limit test open allow unit to cool and retest.
5. If still open, replace the control.

Testing Auxiliary Limit

The auxiliary limit control is a preset nonadjustable control
mounted in the blower compartment area.
It is connected in series with the rollout switch wiring to the
gas valve. If its temperature should be exceeded, it will
open, interrupting the voltage to the gas valve causing it to
open.
An additional limit (primary limit) control is required for
safety control of high temperature within the furnace or
ductwork.
AUX. LIMIT
WARNING
35