Carrier 58stx100 gas furnace shows code 13 at start in the morning


Old 01-15-18, 04:28 PM
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Carrier 58stx100 gas furnace shows code 13 at start in the morning

Please don’t tell me that the furnace “does like early mornings”, my wife did that already.

This furnace is a Carrier 58 STX 110 that has been in use (not much, I live in Los Angeles) since 2004. It run without problems until before Christmas 2017.

Started by running for about 10 minutes and shutting off with code 13. I inspected for obstructions, filter etc…but because of my schedule I decided to call a Heating /AC contractor.

As I expected they inspected the furnace vents, etc. and indicated that the temperature switch on the vent ducting was tripping. I verified that by checking the Resistance (Ω) value and indicated open. They checked the vent for obstruction, the air filters, vents, etc. I was at the base so I go for what the fellow told wife.

They recommended to change the vent temperature sensor/switch for which they asked twenty times the cost of the switch. Since I was on duty I agreed to the repair. They replaced the sensor/switch, run it for ½ hour and declared victory.

When I got home the unit did not come on at 17:00 as scheduled and it was a code 13 flashing again.

We called back and they send a second guy. That day I was home so I stayed with the guy. I must admit he run a thorough and complete inspection and test. His diagnosis was a bad inducer motor. He claimed it was drawing low amperes. I not totally agree with that, I am an Engineer who works daily with electric motors, but again he was the “expert”. To replace the motor, they quoted more money that I paid for my 1965 Mustang, so I ordered the motor, plus the fan. I ordered the fan because the technician claimed that one of the blades had a hole in it. Yes, indeed it had a hole, but that hole is to permit access the Allen wrench to reach and tighten the set screw. My confidence when down fast.

I ordered the parts and changed them myself, including a new gasket. The system run flawlessly all day yesterday. It was not very cold outside but we set it about 72° F and kept the house at the selected temperature by kicking on and off.

At 22:00, the schedule called for 66°F. The system stopped correctly. I checked the LED solid Red, I declared victory and went to bed.

This morning at 06:00 hours did not kick in as the schedule calls for. I checked the LED, code 13. I turned the main switch off and then on. The system started and followed the scheduled temperature; 72°F at 06:00, then 66° F at 10:00 hours.

Please HELP!!!.

I do not why when the temperature goes down below 66°F the system does not kick in. It does not make sense. From 66°F overnight to the setting of 72°F at 06:00 hours is not such a big swing.

The house we had in the mountains, has sometimes, temperature swings of 15°F or more when snowing, and still worked fine.

I will appreciate any help.
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Old 01-15-18, 06:17 PM
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Welcome to the forums.

Well.... the furnace appears to be overheating.... why.... it's not always easy to tell.
Do you feel a good airflow out of the registers ?

Overheating is a common problem. I'll usually check the heat rise by measuring the return temperature and the supply temperature to see if the furnace is running excessively hot. It's very rarely a defective limit switch. Soot on the heat exchanger is one problem as well as a dirty A/C coil.
Old 01-16-18, 11:30 AM
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Thank you Pete!
The technician that was here checked the return as well as the output temperature and made no comment. He drilled holes on the input duct and output and inserted a probe. I have an Omegascope (infrared type gun with laser pointer)and I will use it measure the temperature at each of the holes this gut used for the probe. I will measure as well as the temperature at the safety sensors/switches and the vent ducts. I will report tomorrow.
Cleaning the heat exchanger appears to be doable for me but the A/C coil will require removal or can it be done where it is right now?

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