How many ohms should a high limit switch have?

Each time you press on it, the switch should go from OPEN to CLOSED with each closure being a reliable 0.1 Ohms or less. Anything higher is cause for replacement (Fig.

How can you tell if a high limit switch is bad?

Quote from the video:
Quote from Youtube video: Set your volt meter on ohms. Take your two probes and touch these two contacts. And if it's good it will say zero. Any other reading then it means this upper limit switch is bad.

What should a limit switch read?

The fan limit switch should be open when the furnace is off and full of cool air, so you should get an OL reading; if not, there’s a short, and the switch should be replaced. 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.

At what temperature does a high limit switch open?

The switch commonly operates at an upper limit of 160°F (causing the burner to turn off) and a lower limit of 130°F. The limit switch has two main components: a long temperature sensor located inside the furnace, and a switch mounting plate located on the outside of the furnace.

What is the resistance of furnace limit switch?

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.
Dec 25, 2016

How do you test a furnace switch?

Disconnect the wires connected to the pressure switch by pulling the wire connectors off of the switch terminals. Set a multimeter to test for resistance (ohms). Touch each tester probe to one of the switch terminals. The tester should read 0 or close to 0 (indicating no resistance).
Aug 24, 2021

Can you bypass a high limit switch on a furnace?

Yes, you can bypass the high limit switch for testing.
Dec 18, 2020

Why does my furnace 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. Check your air filter, and replace it if dirty.
Feb 19, 2021

How do you reset a high limit switch on a furnace?

How to Reset a Furnace Limit Switch

  1. Locate your furnace’s heating duct. …
  2. Locate the white limit switch. …
  3. Look at each arm to identify the settings. …
  4. Identify the component (setting) located in between the two arms. …
  5. Set the temperature on the middle component to approximately 105 to 115 degrees Fahrenheit.

What causes high limit opening?

An open high limit error on a furnace means the heating system turns off the fuel to prevent overheating. Ultimately, it is a key safety component of your furnace. A high limit error could be caused by Poor Airflow from the furnace.

How do you test a furnace 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 you Ohm a limit switch?

Quote from the video:
Quote from Youtube video: Put one meter lead on each side of the limit circuit and what you should read is under 1 ohm resistance.

Can you clean a high limit switch?

Remove the high limit switch by removing the two screws that hold it to the plenum. If the flame sensor rod is dirty, you can try cleaning it gently with steel wool or sandpaper, or replace the part with an identical new part.
Apr 27, 2022