How To Bypass A Thermostat For Cooling Or Heating

Bypassing a thermostat is one of the easiest ways to troubleshoot a furnace or an air conditioner that is not heating or cooling. If your AC or furnace is not working,  it’s either the problem lies with the thermostat or with the HVAC system . So how do you know the source of the problem?

One way is to use a multimeter but if you don’t have a multimeter, another option is to bypass your thermostat to see if cooling or heating will be energized.

To bypass a thermostat for cooling when troubleshooting,  put together the  Y wire (yellow) and the R ( red) power from the transformer.  If the system is not energized instantly, wait for the time delay( usually 5 minutes) to elapse.

To bypass a thermostat for  heating in troubleshooting,  put a jumper between  W wire and the Rh. If  you don’t have Rh, use the R wire instead.

To bypass a thermostat for fan, put a jumper between the G and R wire

So you can test cooling, heating or testing by bypassing. It.  Let’s look at each of them in a little detail.

Step by step instruction on how to bypass a thermostat

Here are some of the steps to take before you begin the procedure.

Step 1: Turn off the power to your furnace/ air handler. A furnace switch will typically look like a light switch and be located on the side of the furnace. If you can’t find  the switch turn of the  HVAC system at the main circuit breaker

Step 2:  Remove your thermostat from the wall. This is usually done by pulling the thermostat from the bottom but be careful    some thermostat may have screws that you may need to be removed before pulling it off the wall.

Step 3:   Once the display is off the wall you should see the base with wires attached to it. Here are just some of the most common wires you will see. See a complete thermostat wiring color code guide here

Wire Wire and Designation Function
G ( Green)Controls the fan
Red ( Rc or Rh)From from transformer
White (W)Controls heating
Blue or brown wireProvides consistent power to thermostat
Yellow (Y)Controls cooling

How to Bypass a thermostat  for heating or cooling

To bypass a thermostat for heating or cooling you will need to use alligator jumpers. If you don’t have one you can  use a  wire stripped on its ends. And if you can’t find any wire you can use a paper clip or staples.

On some thermostat you might need to unscrew the terminals so you can insert a jumper wire between the wire the terminal connections

To bypass a thermostat for cooling jump  the Y wire and the R wire. If AC does work,  the problem is probably with the thermostat not the HVAC system.


Is bypassing a thermostat safe?

 Bypassing a thermostat for troubleshooting purposes is generally safe if done correctly and temporarily. However, it’s important to note that tampering with the thermostat or its wiring may void warranties and should not be a permanent solution. If you’re unsure, consult a professional HVAC technician.

Can bypassing your thermostat cause damage to my HVAC system?

 Bypassing your thermostat itself should not cause damage to your HVAC system. However, it’s important to be cautious and avoid making any incorrect or improper connections during the bypass process which could blow up fuses.

What do the results of bypassing a thermostat indicate?

If your HVAC system functions properly when the thermostat is bypassed (e.g., the fan starts running), it suggests that the thermostat may be faulty.

Can I permanently bypass the thermostat?

Bypassing the thermostat should only be done temporarily for testing purposes. The thermostat plays a vital role in regulating temperature and ensuring efficient HVAC system operation. 

If  your HVAC system runs after bypassing your thermostat, you might want to  rewire your thermostat or possibly have it replaced.

Final thoughts

In conclusion, bypassing the thermostat temporarily can help determine if it is the source of an HVAC issue.We hope this guide has been helpful to you. Remember, bypassing should only be done for testing purposes, and a faulty thermostat may require repair or replacement.

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