Carrier 59MN7A Troubleshooting Guide

-1- Replaces: NEW Form: 59MN7A-01T 9-11 Variable Speed, Modulating Electronic Condensing Four-Way Multipoise Gas Furnace 59MN7A S

- 10 - START HERE - If a problem exists, the service technician should always begin troubleshooting here. Special Note: All voltmeters are not the sa

- 11 - STEP ACTION YES NO GO TO 26. Is 115-vac across the transformer leads? 27 25 27. Replace the transformer. 18 28. Is 24-vac across

- 12 - IMPROPER COOLING AIR FLOW - Generally, this indicates the Y/Y2 thermostat lead is not properly connected. If User Interface is connected to

- 13 - Table 2 – Cooling Tonnage vs. Airflow (CFM) AIR CONDITIONING TONS (12,000 BTU/HR) AIRFLOW (CFM) 060, & 3.5T-080 MODEL 5T-080 & 100 MO

- 14 - MINIMUM AND/OR MAXIMUM HEAT TEMPERATURE RISE TOO LOW - Generally, this indicates the furnace is extremely underfired. STEP ACTION YES NO GO

- 15 - Status Code 11 NO PREVIOUS CODE - Stored status codes are erased after 72 hours or can be cleared by jumpering R, W/W1, and Y/Y2 thermostat l

- 16 - STEP ACTION YES NO GO TO 23. The call for heat was probably satisfied during the blower on-delay period, or power to the furnace was probab

- 17 - Status Code 14 IGNITION LOCKOUT - This status code indicates the furnace failed to ignite gas and/or prove flame in 4 attempts. The modulat

- 18 - Status Code 22 ABNORMAL FLAME-PROVING SIGNAL - This status code indicates the flame signal was sensed while gas valve GV was de-energized.

- 19 - Status Code 24 SECONDARY VOLTAGE FUSE IS OPEN - Indicates fuse is open and there is a short in low-voltage wiring. STEP ACTION YES NO GO TO

- 2 - The modulating furnace control was designed with diagnostic capabilities built in. An AMBER LED is used to flash a status code which will lead

- 20 - STEP ACTION YES NO GO TO 36. Does status code 34 flash? If not, status code 24 should occur when BLUE wire is energized. 60 37 37. Tu

- 21 - Status Code 25 MODEL SELECTION OR SETUP ERROR – If status code 25 only flashes 4 times on power-up the modulating furnace control is missing

- 22 - Status Code 31 MEDIUM PRESSURE SWITCH, HIGH PRESSURE SWITCH, OR PSR RELAY DID NOT CLOSE OR REOPENED - This status code can occur under the s

- 23 - down. After the blower off-delay is completed the modulating furnace control will stop displaying status code 31 and if there is a call for h

- 24 - STEP ACTION YES NO GO TO 33. Does the inducer wheel turn freely? 60 32 34. Continue to observe furnace operation for 20 minutes or un

- 25 - Status Code 32 LOW PRESSURE SWITCH DID NOT CLOSE OR REOPENED - This status code can occur as a result of the low pressure switch LPS not maki

- 26 - STEP ACTION YES NO GO TO 34. You have excessive restriction in combustion-air or vent pipe. Also check for proper vent sizing for installa

- 27 - Status Code 33 LIMIT CIRCUIT FAULT - This status code indicates the limit, flame rollout switch is open, or the furnace is operating in maxi

- 28 - STEP ACTION YES NO GO TO 40. Remove tape from door switch, turn power off at main disconnect, and remove jumper across R and W/W1. 41 41.

- 29 - Status Code 34 IGNITION-PROVING FAULT - This status code indicates flame was not sensed during trial for ignition period. The control will

- 3 - When a communicating control is used, the furnace will modulate through its full operation range, or can be limited via the minimum and maximum

- 30 - STEP ACTION YES NO GO TO 32. Clean flame sensor with fine steel wool and make sure it is properly positioned then recheck current. Current

- 31 - Status Code 35 GAS VALVE FAULT - This status code indicates that the modulating gas valve failed to respond to a command from the modulating

- 32 - STEP ACTION YES NO GO TO 25. Do you have continuity between PL8-2 and PL17-2? Note: The terminals in PL8 can be permanently damaged if the

- 33 - Status Code 41 BLOWER MOTOR FAULT - This status code indicates the blower failed to reach 250 RPM or the blower failed to communicate to the

- 34 - STEP ACTION YES NO GO TO 28. Check the blower motor serial output signal. To do this disconnect PL3 from the furnace control and connect a

- 35 - STEP ACTION YES NO GO TO 46. When blower control module is completely detached from blower motor, verify with standard ohmmeter that the re

- 36 - 23. Reconnect PL16 to the inducer motor and put setup switch SW1-6 in the OFF position. 24 24. Does inducer wheel turn freely? 26 25

- 37 - STEP ACTION YES NO GO TO 61. Does a different status code flash? 7 65 62. Is there any frost build-up on combustion-air inlet? 63 64

- 38 - STEP ACTION YES NO GO TO 20. Is 24-vac across GRAY wire on the medium pressure switch MPS and COM-24V on modulating furnace control? 22 21

- 39 - APPENDIX A BOARD LAYOUT AND WIRING SCHEMATICS Fig. 1 – Modulating Furnace Control 24-V THERMOSTAT TERMINALS PL2 – HOT SURFACE IGNITER &

- 4 - 7. Switching from Intermediate-Heat to a Low Range Input - If the furnace control switches from intermediate-heat to a low range input (low r

- 40 - Fig. 2 – Wiring Schematic

- 41 - APPENDIX B ECM BLOWER MOTOR DESCRIPTION & OPERATION The Regal-Beloit Electronically Commutated Motor (ECM) shown in figure 3 is the

- 42 - Figure 3 – ECM Blower Motor

- 43 - APPENDIX C PRESSURE CHECK DIAGRAM PRESSURE SWITCH MAKE/BREAK POINTS UNIT SIZE (BTUH) HIGH PRESSURE SWITCH MEDIUM PRESSURE SWITCH LOW P

- 44 - APPENDIX D STATIC PRESSURE READING LOCATION DIAGRAMS Figure 5 – Upflow Total Static Pressure Reading Locations Figure 6 – Downflow

- 45 - Tools Needed: 1. Pitot Tube 2. Incline Manometer/Magnahelic Example 1: Return ESP after Filter 0.20 in.w.c. Supply ESP

- 46 - APPENDIX E QUICK REFERENCE INFORMATION PRESSURE SWITCH MAKE/BREAK POINTS UNIT SIZE (BTUH) HIGH PRESSURE SWITCH MEDIUM PRESSURE SWITCH

- 47 - APPENDIX F FURNACE STAGING ALGORITHM On initial thermostat call for heat after power-up, furnace staging algorithm will provide 45 secon

- 48 - Replaces: NEW Form: 59MN7A-01T 9-11 Using recorded Modulating rate (MOD%), time of operation at the Modulating rate (MOD

- 5 - changed to intermediate-heat. When the inducer motor speed gets within 15% of the required intermediate-heat RPM the furnace control CPU will

- 6 - Note: The air conditioning relay disable jumper ACRDJ must be disconnected to allow thermostat control of the outdoor unit staging. (See Fig.

- 7 - motor BLWM is operating. The furnace control CPU will shift the continuous-blower airflow from the factory setting to the next highest CF sele

- 8 - SERVICE/STATUS CODE INSTRUCTIONS If status code recall is needed disconnect the “R” thermostat lead, reset power, and put setup switch “SW1

- 9 - 33 LIMIT CIRCUIT FAULT – Indicates the limit, or flame rollout is open or the furnace is operating in maximum-heat only mode due to 2 successi