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Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 20562
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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My name is
, my furnace is short cycling will not stay

Customer Question

Customer: my name is wes
JA: Thanks. Can you give me any more details about your issue?
Customer: 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
JA: OK got it. Last thing — HVAC Technicians generally expect a deposit of about $18 to help with your type of question (you only pay if satisfied). Now I'm going to take you to a page to place a secure deposit with JustAnswer. Don't worry, this chat is saved. After that, we will finish helping you.
Submitted: 1 year ago.
Category: HVAC
Expert:  Rick replied 1 year ago.

What is the brand and model number of your furnace?

Customer: replied 1 year ago.
I'm not sure it has no tag I think it's a Lennox not sure of model has no tags or markings
Expert:  Rick replied 1 year ago.

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

Customer: replied 1 year ago.
Expert:  Rick replied 1 year ago.

What brand?

Customer: replied 1 year ago.
Goodman gmp075 3
Expert:  Rick replied 1 year 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

Customer: replied 1 year ago.
There were three switches none were tripped
Expert:  Rick replied 1 year 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

Expert:  Rick replied 1 year 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

Customer: replied 1 year 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?
Expert:  Rick replied 1 year 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

Customer: replied 1 year 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
Expert:  Rick replied 1 year 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.

Customer: replied 1 year 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
Expert:  Rick replied 1 year ago.


Customer: replied 1 year ago.
Thanks rick
Expert:  Rick replied 1 year ago.

You're welcome

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