TruTech Tools - HVAC School

BACK

Visit Website

TruTech Tools is an online HVAC/R and Building Performance tool distributor. Specializing in HVAC/R and Building Performance tools and test instruments, TruTech has earned a reputation as the go-to source for tools and expertise on the applications for our tools.

We carry 90+ brands of the top tool and test instrument manufacturers and stock the products we sell so that they ship as fast as you can place an order. Have an issue with an order? Want to request a tool be added to our website? Our trained customer service staff is ready to help you get what you need, so you can get back to work faster!

Visit us today at www.TruTechTools.com and get the tools you need to get the job done right.

Check out the Building HVAC Science Podcast, co-hosted by owner Bill Spohn Sr. and Industry Engagement Manager Eric Kaiser on Apple or Spotify and hear conversations between the movers and shakers of HVAC and Building Performance!

Check out our most recent video

How to Evacuate an AC system, Full Vacuum Procedure

Our latest Podcast

HVAC School – For Techs, By Techs

Real training for HVAC ( Heating, Ventilation, Air Conditioning and Refrigeration) Technicians. Including recorded tech training, interviews, diagnostics and general conversations about the trade.

In this short podcast episode, Bryan covers some basics on bi-metal and magnetic switches.

Bi-metal switches are made of two dissimilar metals that are bonded together and are often integrated into motors. When the temperature changes, the metals bend. In an overload circuit, they’re designed to bend and open the circuit in an overheat condition. Mercury thermostats also use these; they have a bulb attached to a bi-metallic coil, which causes it to wind or unwind when heated or cooled. Fan limit switches also use bi-metallic coils. Bi-metallic discs also exist, and they snap open to make or break a circuit.

Bi-metallic switches have a time delay and often auto-reset (with exceptions like rollout switches on furnaces), which is advantageous in some applications. However, they’re also affected by the ambient temperature and are more likely to trip in warm weather and less likely to trip in cold weather. Nuisance trips are more common than in magnetic switches, and they may weld themselves shut and fail closed (though failing open is relatively common as well).

Magnetic switches are usually more external to the equipment or parts they’re protecting (such as in the contactor or starter assembly instead of inside a motor itself). These switches are also more instantaneous and are better for mission-critical applications. These also respond to amperage and aren’t affected by ambient temperature. They’re more likely to fail open than closed.

Compared to bi-metallic technology, magnetic switches trip faster and are better for sudden issues rather than long-term operational overheating. In many cases, we use both of them to get the benefits of each.

Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool.

Purchase your tickets or learn more about the 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

Subscribe to our podcast on your iPhone or Android.

Subscribe to our YouTube channel.

Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android

Search Episodes

Bi-metal & Magnetic Switches – Short #252

08/12/2025

Bryan Orr

Fan Law 2 for Techs w/ Adam Mufich

08/07/2025

Bryan Orr