57
Fig. 86 — Vertical Unit with Staged Gas Heat
Draft Fan Pressure Measurement HM Series
Heat Module
1. Remove air pressure supply tube from fan at pressure switch
connection. See Fig. 87, A.
2. Insert “T” into supply tube. See Fig. 87, B.
3. Attach additional piece of tubing from “T” to pressure switch.
See Fig. 87, C.
4. Connect remaining leg of “T” to pressure measuring device
(measure in. wg). See Fig. 87, D.
NOTE: Connect to “low” side of digital monometer as com
-
bustion blower pressure is negative at test point.
5. Place system in operation and observe pressure reading.
Check chart below to ensure that pressure is greater than
noted for ambient operation.
6. After heater fires, allow unit to operate for 10 to 15 minutes.
Observe pressure reading and check Table 25 to verify pres
-
sure is greater than noted for “steady state.”
Fig. 87 — Draft Fan Pressure Measurement
AIR PRESSURE
SWITCH
FLAME ROLLOUT
SWITCH
FLAME ROLLOUT
SWITCH
FLAME SENSOR
HI LIMIT SWITCH
MANIFOLD
PRESSURE TAP
VENT DUCT
(SUPPLIED BY
OTHERS)
DRAFT INDUCER
MOTOR
DRAFT INDUCER
ASSEMBLY
TWO-STAGE
GAS VALVE
SPARK IGNITER
LOWER
CONDENSATE
FITTING
A
C
B
D