How do I know if my limit switch is bad?

The most common sign of a malfunctioning limit switch is the continuous operation of your furnace’s blower. Just as the limit switch won’t allow the fan to turn on until the warm air has reached the right temperature, the limit switch also shuts down when the air cools to a certain temperature.

How many ohms should a high limit switch read?

1 Answer. The limit switch should show a resistance of very near zero ohms when it is in the closed state. Sometimes your meter may show one or two ohms of resistance due to the meter leads if it has not been calibrated to null out the wire resistance. This would be more noticeable with a digital meter.

How do you Ohm a high limit switch?

How do I know if my limit switch is bad on my furnace?

You will know your high limit switch is engaging or tripping when your furnace “short cycles.” The furnace will turn on normally, run for a little while without producing heat – or without bringing your home’s temperature up to the thermostat set point – and then turn off. The cycle repeats again every few minutes.

Why does my high limit switch keep tripping?

If the air inside your furnace gets too hot, the limit switch trips to prevent overheating. If the furnace high limit switch trips due to overheating, there is likely an airflow issue that is preventing proper air movement through the system. … A dirty filter is the most common cause of airflow issues.

What does a high limit switch do?

The high limit switch shuts down the furnace at a set limit so a clog doesn’t burn out the system. Note that the limit switch has nothing to do with the thermostat. Rather, it is wired in series with the 24-volt control circuit of your furnace.

How do you test a limit switch with a multimeter furnace?

Why do limit switches go bad?

When your furnace doesn’t have proper airflow, like when it is operating with a dirty filter, your heat exchanger will repeatedly overheat and put your limit switch through excess wear and tear. This can eventually cause it to malfunction.

Is a high limit switch normally open or closed?

The high limit switch should be closed when the furnace is cold, so you should get a zero reading; if you get the opposite, replace the switch. … Turn off the furnace and if the blower doesn’t go off after about five minutes, the switch is still closed.

Can you bypass furnace limit switch?

If the temperature is below the setpoint, the resistance across the switch should be zero. If you do not have an electrical meter, you can temporarily bypass the switch and see if the furnace works.

How do you test a fan limit switch?

Watch the oil or gas burner: The furnace oil or gas burner should turn ON and subsequently the FAN LIMIT control should turn the burner back OFF when the temperature in the supply air plenum reaches the FAN LIMIT set point. Watch the dial on the fan limit switch moving to confirm its operation.

How do I fix Open High Limit device?

Where is the reset button on a limit switch?

The High Limit Reset Button is located behind the gas valve. 3. Reach your hand on top of the box labeled high limit reset button to feel for the red button.