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, my furnace is short cycling will not stay…

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My name is wes...

My name is wes

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My name is ***** ***** furnace is short cycling will not stay on to reach thermostat temp, I show a 4 code on my board,limit switch

Submitted: 2 years ago.Category: HVAC
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1/23/2016
HVAC Technician: Rick, HVAC Supervisor replied 2 years ago
Rick
Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 23,972
Experience: 40+ yrs. experience as a licensed oil & gas technician.
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What is the brand and model number of your furnace?

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Customer reply replied 2 years ago
I'm not sure it has no tag I think it's a Lennox not sure of model has no tags or markings
HVAC Technician: Rick, HVAC Supervisor replied 2 years ago

There should be a rating tag inside the burner compartment. Look there

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Customer reply replied 2 years ago
Sbm14
HVAC Technician: Rick, HVAC Supervisor replied 2 years ago

What brand?

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Customer reply replied 2 years ago
Goodman gmp075 3
HVAC Technician: Rick, HVAC Supervisor replied 2 years ago

Ok, a 4 blink code is an open limit circuit. The easiest thing is to try resetting the roll out out switch(es) (see attached pic for typical). They are located just outside the burner chamber. Turn the power off to the unit then try pushing the small button between the 2 leads on the switch. If it clicks you have reset it and the unit will fire up when you turn the power back on with any luck. If it doesn't click it wasn't tripped

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Customer reply replied 2 years ago
There were three switches none were tripped
HVAC Technician: Rick, HVAC Supervisor replied 2 years ago

Then you either have a bad limit (the furnace should have cooled down by now) or a bad connection in the limit circuit. You can try checking all the connections on the limit circuit. That would be the wire the rollouts are connected to

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HVAC Technician: Rick, HVAC Supervisor replied 2 years ago

The main limit is on it's own circuit on this model. Red wire. The limit is a rectangular "patch" with 2 terminals located above the burners where it can be inserted into the heat exchnger

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Customer reply replied 2 years ago
All wires are purple there are 4 total 1 is on blower cage 1 top if heat exchanger then 1 on each side there is also 1 on bottom it is same type if button switch just different reset button one on blower box has no reset button so one or all are bad how do you check?
HVAC Technician: Rick, HVAC Supervisor replied 2 years ago

Like I said before the main limit on this model is on a different circuit that the rollouts, it has a red wire. You need a continuity tester to check these devices

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Customer reply replied 2 years ago
I see it it has a black plastic mounting plate with 2 red wires I don't have my tester with me it's at my shop can I jump them together or should I just wait and test it
HVAC Technician: Rick, HVAC Supervisor replied 2 years ago

You can't run the furnace with it jumped out but you could test it. If the furnace doesn't lockout then the limit is probably bad since the furnace must be cold by now or if it locks out after running for a while you could have an air flow problem from a clogged AC coil or a dirty filter.

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Customer reply replied 2 years ago
Filter is new started there I have never cleaned the bottom side of the A coil I checked the top from access panel but can't see bottom which is where it would be dirty will check it after work tommorow if I can figure out how to get to it
HVAC Technician: Rick, HVAC Supervisor replied 2 years ago

ok

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Customer reply replied 2 years ago
Thanks rick
HVAC Technician: Rick, HVAC Supervisor replied 2 years ago

You're welcome

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