High Heat Temperature Rise Too Low - Bryant 355MAV Troubleshooting Manual

AIR CONDITIONING TONS
(12,000 BTU/HR)
1-1/2
2-1/2
3-1/2
HIGH HEAT TEMPERATURE RISE TOO LOW - Generally, this indicates the HI solenoid in gas
valve GV has failed or the furnace is extremely underfired.
STEP
1. Remove the blower access panel. Disconnect User Interface ABCD connector (if used) or the
R thermostat lead (if used) from the furnace control board. If setup switch SW1-2 is ON then
set it to OFF.
2. Depress the door switch. Use piece of tape to hold it closed.
3. Jumper R and W/W1 thermostat terminals.
4. When the furnace is running in low heat, clock the low heat gas rate. You have 16 minutes on
this first call for heat before unit switches to high heat. On propane installations check the
manifold pressure.
5. When the furnace is running in high heat, clock the high heat gas rate. On propane
installations check the manifold pressure.
6. Is the high heat rate approximately the same as the low heat rate?
7. Do you have 24 vac across gas valve terminals HI and C
high heat?
8. You have an open wire or bad terminal on the BROWN wire from the high heat pressure
switch HPS to the gas valve GV. Repair it or replace the harness.
9. Go to the page number indicated in Index for the CLEANUP AND STARTUP
INSTRUCTIONS.
10. Replace the gas valve.
11. Is the high heat rate within 2% of that specified on the rating plate?
Table 2 – Cooling Tonnage vs. Airflow (CFM)
AIRFLOW
(CFM)
525
2 700
875
3 1050
1225
4 1400
1750
5
6 2100
AIR CONDITIONING (A/C) OR CONTINUOUS-FAN (CF)
AIRFLOW SELECTION CHART
BASED ON 350 CFM/TON (SETUP SWITCH SW1-5 OFF)
MODEL
SIZE
040, 060, 3T-080 DEF. 525
5T-080, 100 DEF. 700
120 DEF. 700
BASED ON 400 CFM/TON (SETUP SWITCH SW1-5 ON)
MODEL
SIZE
040, 060, 3T-080 DEF. 600
5T-080, 100 DEF. 800
120 DEF. 800
1. DEFAULT A/C AIRFLOW WHEN A/C SWITCHES ARE IN OFF POSITION
2. DEFAULT CONT. FAN AIRFLOW WHEN CF SWITCHES ARE IN OFF POSITION
3. SWITCH POSITIONS ARE ALSO SHOWN ON FURNACE WIRING DIAGRAM
ACTION
040, 060, & 3T-
080 MODEL
X
X
X
X
X
SETUP SWITCH SW3 POSITIONS
700 875 1050 1225
2 1
875 1050 1225 1400
2
875 1050 1225 1400
2
SETUP SWITCH SW3 POSITIONS
800 1000 1200 1400
2 1
1000 1200 1400 1600
2
1000 1200 1400 1600
2
-24V on 2-stage gas valve during
OM
- 12 -
5T-080 & 100 120 MODEL
MODEL
X X
X X
X X
X X
X X
X X
X
1225 1225
1750 1750
1
1750 2100
1
1400 1400
2000 2000
1
2000 2100
1
YES NO
7 11
10
13 12
GO TO
2
3
4
5
6
8
9
INDEX
9