Commercial Refrigeration for A/C Techs w/ Dick Wirz

By August 28, 2017

Commercial Refrigeration for A/C Techs w/ Dick Wirz

Dick Wirz, author of “Commercial Refrigeration for Air Conditioning Technicians” talks about making the switch to refrigeration, Evaporator split, defrost and more…

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 talks about motor speed and other basic electrical topics as they relate to motors in HVAC equipment.

In a typical single-phase PSC-type (induction-driven) motor, the speed is primarily determined by the electrical cycle rate, also known as the hertz. The hertz represents the speed at which the electrical current changes direction (positive to negative) per second; in the USA, that number is typically 60 hertz. Unless we’re dealing with ECMs and VFD-driven motors, the motor speed will be partially influenced by the hertz or frequency as determined by the utility company or a generator.

Motor speed is also determined by the number of magnetic poles in the motor. A motor doesn’t make a complete revolution per cycle; a cycle only refers to the distance between two poles. The more poles we have, the shorter the distance needs to turn per cycle. A two-pole motor rotates all the way every cycle, resulting in 3600 RPM under no-slip conditions (synchronous speed). A four-pole motor has half the RPM, and an eight-pole motor has 1/4 of the RPM of a two-pole motor.

Speed taps add winding resistance between run and common to create slip and slow the motor. A six-pole motor has 1200 RPM synchronous, but 1075 is the effective speed with slip factored in. Each speed has a different level of winding resistance, which slows the motor as you move from high to low; the lower-speed tap has higher resistance than high-speed taps.

ECMs and VFD-driven systems convert the frequency and don’t depend on the electrical frequency from the utility or generator.

Learn more about the HVACR Training Symposium or buy a virtual ticket today at https://hvacrschool.com/symposium.

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Check out our handy calculators HERE.

Search Episodes

Motor Speed – Short #164

05/30/2023

Bryan Orr

Growing in Productivity and Confidence as a Tech w/ Refrigeration Mentor

05/25/2023

Bryan Orr

The Art of Unteaching w/ MeanHVAC

05/18/2023

Bryan Orr

Floating vs. Fixed Suction and Head – Short #163

05/16/2023

Bryan Orr

Humidity Utopia w/ Nikki & Bryan

05/11/2023

Bryan Orr

What the Flux? – Short #162

05/09/2023

Bryan Orr

The Impacts of Duct Leakage w/ Steve Rogers

05/04/2023

Bryan Orr

Launch of the Sensi Touch 2 Thermostat

05/02/2023

Bryan Orr

Why and How to Create an Internal Training Program W/ Eugene S.

04/27/2023

Bryan Orr

When Subcooling is Meaningless – Short #161

04/25/2023

Bryan Orr

Search Results placeholder

Related Tech Tips

How to Compare Heat Sources For Cost Effectiveness

This article is based on Ross Trethewey’s energy comparison sheet for fuels at select efficiencies and costs. All tables and their respective data belong to him. Ross Trethewey is the founder and lead engineer of TE2 Engineering and has served as the Home Technology Expert on “This Old House.” You can find a PDF file […]

Pitch on Line Penetrations

Most techs and installers know that drains need to be pitched. I use the rule of thumb that drain lines should generally be pitched 1/4″ per foot of horizontal run. One thing that can easily be forgotten is pitching wall penetrations when drilling. It's as simple as drilling with a slight upward angle if drilling […]

Trades and the Skills Gap - A Manifesto

This article is a year old, and I'm recycling it because it's on my mind today. I had a fun conversation with Richard Trethewey on the podcast that has me thinking along these lines today. The link is HERE if the player isn't showing up. I have a confession to make. I'm a bit of […]

More tech tips