Adjustments - Bryant 312A Installation, Start-Up, Operating And Service And Maintenance Instructions

SETUP SWITCH
SWITCH NO. NAME
SW--- 1 Adaptive Heat Mode
SW--- 2 Blower OFF delay
SW--- 3 Blower OFF delay
Step 3 — Adjustments
WARNING
!
FIRE HAZARD
Failure to follow this warning could result in injury, death
and/or property damage.
DO NOT bottom out gas valve regulator adjusting screw.
This can result in unregulated manifold pressure and result
in excess over- -fire and heat exchanger failures.
CAUTION
!
FURNACE DAMAGE HAZARD
Failure to follow this caution may result in reduced furnace
life.
DO NOT re- -drill orifices. Improper drilling (burrs, out- -of
round holes, etc.) can cause excessive burner noise and
misdirection of burner flames. This can result in flame
impingement of heat exchangers, causing failures. (See Fig.
50.)
Furnace gas input rate on rating plate is for installations at
altitudes up to 2000 ft Furnace input rate must be within +/- -2%
of furnace rating plate input. For altitudes above 5500 ft, a
field- -supplied high altitude pressure switch is required.
1. Determine the correct gas input rate.
In the U.S.:
The input rating for altitudes above 2,000 ft must be re-
duced by 4% for each 1,000 ft above sea level.
For installations below 2000 ft, refer to the unit rating
plate.
For installations above 2000 ft, multiply the input on the
rating plate by the derate multiplier in Table 11 for the cor-
rect input rate.
EXAMPLE:
88,000 BTUH INPUT FURNACE INSTALLED AT 4300 FT
Derate
Furnace Input Rate X Multiplier
at Sea Level Factor
88,000 X 0.90
In Canada: The input rating must be reduced by 10% for
altitudes of 2,000 ft to 4,500 ft above sea level by an
authorized Gas Conversion Station or Dealer. To
determine correct input rate for altitude, see example and
use 0.90 as derate multiplier factor.
2. Determine the correct orifice and manifold pressure
adjustment. All models in all positions except Low NOx
Table 10 – 2- -Stage Furnace Setup Switch Description
NORMAL
POSITION
When OFF, allows 2--- stage operation with a single stage thermostat.
Turn ON when using 2 stage thermostat to allow Low Heat opera---
OFF
ON or OFF
ON or OFF
Furnace Input Rate
= at Installation
Altitude
= 79,200
DESCRIPTION
OF USE
tion when R to W/W1 closes and High Heat operation when R to
W/W1 and W2 close.
Control blower OFF delay time. Used in conjunction with SW--- 3.
See Table 14.
Control blower OFF delay time. Used in conjunction with SW--- 2.
See Table 14.
models in downflow and horizontal positions use Table 15
(22,000 BTUH per burner).
Table 11 – Altitude Derate Multiplier for U.S.A.
ALTITUDE %
(FT) OF DERATE
0–2000 0
2001–3000 8–12
3001–4000 12–16
4001–5000 16–20
5001–6000 20–24
6001–7000 24–28
7001–8000 28–32
8001–9000 32–36
9001–10,000 36–40
* Derate multiplier factors are based on midpoint altitude for altitude
range.
Low NOx models in downflow or horizontal positions MUST
use Table 16 (21,000 BTUH per burner). See input listed on
rating plate.
a. Obtain average yearly gas heat value (at installed altitude)
from local gas supplier.
b. Obtain average yearly gas specific gravity from local gas
supplier.
c. Find installation altitude in Table 15 or 16.
d. Find closest natural gas heat value and specific gravity
in Table 15 or 16
e. Follow heat value and specific gravity lines to point of
intersection to find orifice size and low- -and high- -heat
manifold pressure settings for proper operation.
f. Check and verify burner orifice size in furnace. NEVER
ASSUME ORIFICE SIZE. ALWAYS CHECK AND
VERIFY.
g. Replace orifice with correct size, if required by Table 15
or 16. Use only factory- -supplied orifices. See
EXAMPLE 2.
EXAMPLE 2: (0- -2000 ft altitude)
For 22,000 Btuh per burner application, use Table 15.
Heating value = 1000 Btuh/cu ft
Specific gravity = 0.62
Therefore: Orifice No. 43*
Manifold pressure: 3.7- -in. wc for high- -heat
1.6- -in. wc for low- -heat
* Furnace is shipped with No. 43 orifices. In this example
all main burner orifices are the correct size and do not need
to be changed to obtain proper input rate.
3. Adjust manifold pressure to obtain low fire input rate. (See
Fig. 54.)
36
DERATE MULTIPLIER
FACTOR*
1.00
0.90
0.86
0.82
0.78
0.74
0.70
0.66
0.62