Carrier Furnace 33 to 13


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Old 03-26-24, 12:34 PM
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Carrier Furnace 33 to 13

Hello Folks,

I am troubleshooting an issue with carrier furnace Model 59SP2A080E21. This has been going on for months.

Most mornings, when it kicks off at 5 am, it will try to run but goes to 33, there is no power at Thermostat. In about 30 minutes, power is restored to NEST. The code is then 13. I will then reset power at CB, wait 30 minutes. And then try to start. Then it will run fine all day, sometimes for days. The cycle repeats every few days. Sometimes, i have to reset it twice or 3 times to make it work. But once is starts, it will run fine. It will auto stop for many hours due to temp reached, and then restart fine as well. Looks like it needs a jump start in the morning, due to cold ?

Called technician. He first increased fan speed, and maybe lower gas. That did not help
Then he changed the limit switch. Did not help
Now he is planning to change the circuit board. Not yet agreed to that

I tried to find the capacitor myself, i dont see one

Any clues please, what could be wrong ?
Thanks a lot
Ash
 
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Old 03-26-24, 12:44 PM
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Welcome to the forums.

Fault code 33 is an opening high limit or flame rollout switch.
When any of those switches opens..... the 24v power to the thermostat is cut and typically the blower and inducer run but not the burner.

You need to locate all the limit switches and test them when the furnace faults.
Ultimately it's an over temp issue.
Restricted air flow, dirty air filter, dirty A/C coil, blocked returns, closed registers, etc.
 
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Old 03-26-24, 01:09 PM
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Thanks Pete. If that was the case, how does it explain that it runs fine once it starts, and the burner is also running as it heats up the house. Its not just the blower...

This issue mostly happens early morning, when its cold. It does not even start, so over heating does not seem to be the case, because there are days when it has run continuously for over an hour without stopping. So it will run fine all day, but will not start the next day morning. Once i reset, it starts working fine again. Sometimes, it will run for days with requiring reset. I have new filters, and all outlets are fully open
 

Last edited by Ashik; 03-26-24 at 03:53 PM.
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Old 03-27-24, 10:41 AM
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Update - i checked the flame roll out switch and looks very clean, but i still cleaned it.
The limit switch is already new
All filters have been replaced.
All registers are open
Could the problem be with the motor, during initial start when its cold ? I checked and there is no capacitor in there. Anything else i can check to resolve this issue on my own ?
Thanks
Ash
 
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Old 03-27-24, 05:39 PM
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There is more than one limit switch. The manual shows three.
Flame rollouts and limit.

It sounds like you have a blower problem.
If the blower doesn't run the unit will shut down on overheat.

Page 81 describes the heating cycle.
Furnace manual - pdf


Looking at the wiring diagram.... you can follow the red/24v R path. (page 85)
All three switches must be closed to get 24v on the R terminal.
If you look at the connection diagram on the left..... the red sensor loop runs from pin 6 to pin 8 on the 12 pin plug on the board. I connect my meter directly to pins 6 and 8. There should be very close to 0v measured. If you see anything above 1/2v ...... there is a problem in the loop.

In some cases the 12 pin plug and socket gets corroded. Unplugging and plugging the plug several times will clean it.
 
 

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