Service Manual

SERVICING
50
RETURN
SUPPLY
INCLINED
MANOMETER
Total External Static
2. Measure the static pressure of the supply duct, (Positive
Pressure).
3. Add the two readings together.
NOTE: Both readings may be taken simultaneously and read
directly on the manometer if so desired.
4. Consult proper table for quantity of air.
If the external static pressure exceeds the minimum or
maximum allowable statics, check for closed dampers, dirty
filters, undersized or poorly laid out ductwork.
S-201 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.
RETURN
SUPPLY
SUPPLY
T
RETURN
T
RISE = SUPPLY -
T
RETURN
T
Checking Temperature Rise
S-300 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.
Volt / Ohm
Meter
COLOR
IDENTIFYING
SLEEVES
TESTING PRIMARY LIMIT CONTROL
Refer to the specification section to determine the proper limit
cutout temperature for the model being serviced.