Carrier 58MVP Troubleshooting Manual page 11

STEP
23. Turn power off and reconnect thermostat leads to furnace control board.
24. Turn power on.
25. Does RED LED2 turn back ON?
26. Disconnect all thermostat leads from thermostat control board.
Put setup switch SW-1 in ON position and jumper R, W/W1, and Y/Y2 thermo-
27.
stat terminals simultaneously until RED LED2 turns OFF.
28. Put setup switch SW-1 back in OFF position.
29. Jumper R and W/W1 thermostat terminals.
30. Does RED LED2 turn back ON?
Install isolation relays in the W/W1 and Y/Y2 circuits per Fig. 2 in Appendix B or
31.
replace thermostat.
32. Was RED LED2 ON before you started Step 1?
Solid YELLOW LED3 indicates furnace is in high fire and solid GREEN LED4
33.
indicates furnace is in low fire.
Check outdoor unit contactor. Failure to pull in can cause excessive current
draw on low-voltage circuit. This can be intermittent and may require extended
34.
operation to repeat problem. Isolating outdoor unit may solve problem. (See Fig.
3 in Appendix B.)
Check thermostat wire gage between furnace and outdoor unit. It is recom-
35. mended that AWG No. 18 color-coded copper thermostat wire be used for
lengths up to 100 ft. For wire lengths over 100 ft, use AWG No. 16 wire.
Observe operation of furnace through a 20 minute heat cycle. Try to pinpoint
36.
where in cycle RED LED2 turns ON.
Go to step indicated below if RED LED2 turns ON when 1 of the following
events occur:
• When gas valve is energized.
37.
• When HSI is energized.
• When high-pressure switch HPS makes during transition from low to high fire.
• RED LED2 never turns ON.
38. Replace gas valve.
Isolate humidifier with a separate 24-vac supply or replace humidifier solenoid
39.
coil.
Observe operation of furnace through a 4 minute cooling cycle. Does RED
40.
LED2 turn ON?
41. Disconnect all thermostat leads from furnace control board.
Put setup switch SW-1 in ON position and jumper R, W/W1, and Y/Y2 thermo-
42.
stat terminals simultaneously until RED LED2 turns OFF.
43. Put setup switch SW-1 back in OFF position.
Reconnect only outdoor unit to Y/Y2 and Com terminals on furnace control
44.
board.
45. Jumper R and Y/Y2 thermostat terminals.
46. Does RED LED2 turn back ON?
Go to page number indicated in Index for CLEANUP AND START-UP
INSTRUCTIONS. If problem persists on an intermittent basis, replace furnace
47.
control board. If problem still persists on an intermittent basis after replacing
furnace control board, contact your distributor.
RED LED2 FLASHING—Indicates line voltage polarity is reversed.
STEP
Turn power off, remove blower access panel, and disconnect all thermostat
1.
leads from furnace control board.
Turn power on and depress door switch. Use a piece of tape to hold switch
2.
closed.
3. Is RED LED2 flashing?
4. Replace furnace control board, date code 9405 or later.
Go to page number indicated in Index for CLEANUP AND START-UP
5.
INSTRUCTIONS.
6. Do you have 120 vac across L2 and chassis ground?
7. Line voltage polarity is reversed. Fix problem.
8. Replace furnace control board.
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