Refrigeration / Components & Accessories / Compressors

Ice Breaker: High-Pressure Switches

Troubleshooting Compressor Shutdown Controls Requires Care

High-pressure switches are used on many refrigeration systems. They are designed to shut down a compressor if the system’s high pressure rises above an unsafe level, not allowing the compressor to restart until the pressure returns to a safe level. High-pressure switches are available with either an automatic or manual reset.

Joe Marchese
Joe Marchese

An automatic reset will automatically restart the compressor when the pressure falls to a safe value. A manual-reset high-pressure switch needs to have an operator manually press a reset button in order to restart the compressor. They are also available with either an adjustable cut-out setting that could be adjusted by a technician, or fixed settings, which cannot be adjusted by a technician.

When making field adjustments to the adjustable high-pressure switch, it is always best to follow the directions or requirements of the system manufacturer. When the manufacturer’s guidelines are not available, the cut-out setting can be set at a saturation pressure equivalent to a 155?F condensing temperature, or 60? above the normal maximum ambient.

When troubleshooting, it is important to not allow a system to run with its high-pressure switch electrically bypassed as it could potentially lead to a very dangerous operating condition.

I can personally attest to this potential safety hazard.

Early on in my career I was called out to repair a system. When I arrived on the job, I noticed it had tripped on its high-pressure switch. I attached my gauges, reset the high-pressure switch, and, sure enough, the high-side pressure steadily increased to the trip point of the high-pressure switch and shut down the system again.

Not knowing the true cause of the problem, I decided to electrically bypass the high-pressure switch. (That was not a very smart decision, as you will see shortly.) I restarted the system and the high-side pressure again started to rise. I watched as it continued to rise well beyond the trip point of the pressure switch, so I decided to shut down the system. Again, being an inexperienced technician, I decided to start the system up again. Not sure why I needed to see the pressure rise again, but I did.

Just as I restarted the system for a second time, my pager went off (this was back in the day, before we had cell phones). So I made mistake No. 2 and left the system running while I went to find a phone to call the office. A few minutes into my phone conversation, I heard a loud explosion and I, along with everyone in the area, immediately ran out. Needless to say, the explosion was actually an 8-inch section of the discharge line (from the unit I was servicing) blowing out of the system. Apparently the system pressure had built up so severely that this section of discharge line broke free and was jettisoned across the room. It actually took down several lights and got wedged into a wall close by.

If I had been there or another person was walking close by we could have been severely injured. Lucky for me, my company and my customer emerged uninjured. But it was definitely a lesson well-learned.

Publication date: 3/31/2014 

Want more HVAC industry news and information? Join The NEWS on Facebook, Twitter, and LinkedIn today!

Did you enjoy this article? Click here to subscribe to The NEWS Magazine

Recent Articles by Joe Marchese

You must login or register in order to post a comment.



Image Galleries

2014 Energy Efficiency Forum

Highlights from the 25th annual Energy Efficiency Forum in Washington, D.C.


NEWSMakers: Mark Satterfield

Mark Satterfield, founder and CEO of Gentle Rain Marketing Inc. and author of “The One Week Marketing Plan” talks about his book and the importance of HVAC blogging. Posted on Sept. 19.

More Podcasts


NEWS 09-15-14 cover

2014 September 15

Check out the weekly edition of The NEWS today!

Table Of Contents Subscribe

Venting R-22

The NEWS reported that a man received prison time for venting R-22. Should EPA step up enforcement?
View Results Poll Archive


2014 National Plumbing & HVAC Estimator

Every plumbing and HVAC estimator can use the cost estimates in this practical manual!

More Products

Clear Seas Research


Clear Seas ResearchWith access to over one million professionals and more than 60 industry-specific publications, Clear Seas Research offers relevant insights from those who know your industry best. Let us customize a market research solution that exceeds your marketing goals.


Magazine image
Register today for complete access to Get full access to the latest features, Extra Edition, and more.


facebook icontwitter iconyoutube iconLinkedIn i con