35
Gas Line
Gas
Shutoff
Valve
Gas Line
To Furnace
Drip Leg Cap
With Fitting
Manometer Hose
Measuring Inlet Gas Pressure (alt. Method)
Figure 48
G
AS
M
ANIFOLD
P
RESSURE
M
EASUREMENT
AND
A
DJUSTMENT
T
O
PREVENT
UNRELIABLE
OPERATION
OR
EQUIPMENT
DAMAGE
,
THE
GAS
MANIFOLD
PRESSURE
MUST
BE
AS
SPECIFIED
ON
THE
UNIT
RATING
PLATE
. O
NLY
MINOR
ADJUSTMENTS
SHOULD
BE
MADE
BY
ADJUSTING
THE
GAS
VALVE
PRESSURE
REGULATOR
.
CAUTION
Only small variations in gas pressure should be made by
adjusting the gas valve pressure regulator. The manifold
pressure must be measured with the burners operating. To
measure and adjust the manifold pressure, use the following
procedure.
1. Turn OFF gas to furnace at the manual gas shutoff valve
external to the furnace.
2. Turn off all electrical power to the system.
3. Outlet pressure tap connections:
a. Honeywell VR9205 valve: Remove the outlet pressure
tap plug. Install an 1/8" NPT hose barb fitting into the
outlet pressure tap.
b. White-Rodgers 36J54 valve: Back outlet pressure test
screw (inlet/outlet pressure tap) out one turn
(counterclockwise, not more than one turn).
4. Attach a hose and manometer to the outlet pressure barb
fitting (Honeywell valve) or outlet pressure tap (White-
Rodgers valve).
5. Turn ON the gas supply.
6. Turn on power and close thermostat “R” and “W1”
contacts to provide a call for low stage heat.
7. Measure the gas manifold pressure with burners firing.
Adjust manifold pressure using the
Manifold Gas Pressure
table shown below.
8. Remove regulator cover screw from the low (LO) outlet
pressure regulator adjust tower and turn screw clockwise
to increase pressure or counterclockwise to decrease
pressure. Replace regulator cover screw.
9. Close thermostat “R” and “W2” contacts to provide a call
for high stage heat.
10. Remove regulator cover screw from the high (HI) outlet
pressure regulator adjust tower and turn screw clockwise
to increase pressure or counterclockwise to decrease
pressure. Replace regulator cover screw.
11. Turn off all electrical power and gas supply to the system.
12. Remove the manometer hose from the hose barb fitting
or outlet pressure tap.
13. Replace outlet pressure tap:
a. Honeywell VR9205 valve: Remove the 1/8" NPT hose
barb fitting from the outlet pressure tap. Replace the
outlet pressure tap plug and seal with a high quality
thread sealer.
b. White-Rodgers 36J54 valve: Turn outlet pressure test
screw in to seal pressure port (clockwise, 7 in-lb
minimum).
14. Turn on electrical power and gas supply to the system.
15. Close thermostat contacts “R” and “W1/W2” to energize
the valve.
Using a leak detection solution or soap suds, check for leaks
at outlet pressure tap plug (Honeywell valve) or screw (White-
Rodgers valve). Bubbles forming indicate a leak. SHUT OFF
GAS AND REPAIR ALL LEAKS IMMEDIATELY!
NOTE:
For gas to gas conversion, consult your dealer for
appropriate conversion.
Range
Nom inal
Natural
Low Stage 1.6 - 2.2" w .c.
1.9" w .c.
High Stage
3.2 - 3.8" w .c.
3.5" w .c.
Propane
Low Stage 5.7 - 6.3" w .c.
6.0" w .c.
High Stage 9.7 - 10.3" w .c. 10.0" w .c.
Manifold Gas Pressure
Gas
G
AS
I
NPUT
R
ATE
M
EASUREMENT
(N
ATURAL
G
AS
O
NLY
)
The actual gas input rate to the furnace must never be greater
than that specified on the unit rating plate. To measure
natural gas input using the gas meter, use the following
procedure.
1. Turn OFF the gas supply to all other gas-burning appliances
except the furnace.
2. While the furnace is operating at high fire rate, time
and record one complete revolution of the gas meter dial,
measuring the smallest quantity, usually the dial that
indicates 1/2 cu. ft. per revolution. You will use this
number to calculate the quantity of gas in cubic ft. if
the furnace would consume if it ran steadily for one
hour (3600 seconds).
3. If the 1/2 cu. ft. dial was used, multiply your number
x 2.
EXAMPLE: If it took 23 seconds to complete one
revolution of the 1/2 ft. dial (23 x 2 = 46).
This tells us that at this rate, it would take 46 seconds to
consume one cu. ft. of gas. 3600 / 46 = 78.
This tells us that in one hour, the furnace would consume 78
cu. ft. of gas.
