Carrier 59MN7A Troubleshooting Guide download pdf (Page 21)

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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 its model plug (PL4) and is defaulting to the model selection stored in memory.

If status code 25 flashes continuously it could indicate any of the following:

1. Model plug (PL4) is missing and there is no valid model stored in permanent memory. This will happen if you forget to

install the model plug (PL4) on a service replacement board.

2. Thermostat call with SW1-1 ON.

3. Thermostat call with SW1-6 ON.

4. SW1-1 and SW1-6 both ON together.

5. Two different furnace models twinned.

6. Service replacement control is incorrect. Need modulating furnace control with software version V17 or later.

STEP ACTION YES NO GO TO

1. Turn power off, remove the blower door, and disconnect User Interface ABCD connector (if

used) or the R thermostat lead (if used) from the furnace control board.

2. Turn power on and depress door switch. Use a piece of tape to hold switch closed. 3

3. Does status code 25 flash only 4 times on power-up? 4 6

4. The model plug is missing or invalid but the control will default to the model stored in

memory. The furnace will operate properly as if the model plug was installed. If you have the

APM program you can confirm the setting in memory.

5. Go to page number indicated in Index for CLEANUP AND START-UP INSTRUCTIONS. INDEX

6. Is setup switch SW1-1 in the ON position? 7 8

7. Put setup switch SW1-1 in the OFF position. 5

8. Is setup switch SW1-6 in the ON position? 9 10

9. Put setup switch SW1-6 in the OFF position. 5

10. Is this a new service replacement control? 19 13

11. You need to remove the model plug PL4 from the old control and install it on the new

replacement control. Once you install the model plug the power to the furnace needs to be

reset because the model plug is only read on power-up.

12. If the model plug is not available from the old control, reference the resistance values on the

rating plate along with the model plug part number. If absolutely necessary you can install two

resistors into the PL4 connection on the control board. R1 goes across the middle 2 pins and

R2 goes across the outer 2 pins. Resistors can be purchased at a nearby Radio Shack. The

resistors need to be within 10% of the stated value. Check with an ohm meter before installing.

13. Is this furnace twinned with another furnace? 14 17

14. Is the MAIN furnace flashing the status code? 15 17

15. Do the furnaces have the same model number on the rating plate? 18 16

16. Replace one of the furnaces because you cannot twin different size furnaces. 5

17. Replace the modulating furnace control. 5

18. One of the model plugs is bad. Ohm out each resistor and replace the one that does not match

the resistance values on the rating plate.

19. Is the model plug PL4 from the old control installed? 20 11

20. Make sure the service replacement control is correct. You need a modulating board with

software version V17 or later. The version of software is printed in the WHITE box near the

L2 terminals on the right side of the furnace control. Reference Figure 1 in Appendix A for the

location of the software version.

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Carrier 59MN7A Troubleshooting Guide Page 21

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