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Lennox g40uh open limit switch? Causes? 6hrs. I can get it…

Customer Question
Lennox g40uh open limit...

Lennox g40uh open limit switch? Causes?

Contractor's Assistant: I'll do all I can to help. How long have you been dealing with this?

6hrs

Contractor's Assistant: Do you plan on doing the work yourself?

Yep

Contractor's Assistant: Anything else we should know to help you best?

I can get it to run eventually after 30-40 minutes. Then shuts off with open limit switch code

Submitted: 8 months ago.Category: HVAC
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Answered in 1 minute by:
11/10/2017
HVAC Technician: airheatman, HVAC Technician replied 8 months ago
airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 9,199
Experience: Furnace, A/C and heat pump specialist.
Verified

To determine if limit is defective or if unit is actually getting to hot, allow unit to shut down on high limit and give us the error code. immediately remove the limit and stick a probe thermometer into the plenum to read actual temperature in chamber.

The limit will have a rating like 175-20 marked on it.(This means it opens at 175 and re closes at 155 degrees.

If limit is opening at a lower temperature than rated for the limit is defective.If chamber is indeed getting hotter than rating, limit is doing its job and you must determine why it is overheating

iI unit is getting too hot below are some things to check and probable causes:

1.Dirty filter

2. Dirty ecaporator coil

3.Blower not running fast enough moving enough air across heat chamber

4.Retricion in ductwork

5.Blocked return air

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