Get an EEV Open (Like Magic)

By April 7, 2018

Get an EEV Open (Like Magic)

This tech tip comes from our contributor, compressor decapitator, and super tech Ulises Palacios.

Many ductless systems and some high-efficiency unitary systems have electronic expansion valves.

If you find one that is stuck closed, you may be able to get it open temporarily by putting a strong magnet like the one shown above on the valve body and turning it counterclockwise.

This is likely only temporary, so valve replacement is still needed. However, it can help get the customer's equipment running while you wait to get a new valve.

Pretty cool, Ulises.

—Bryan

P.S. – if you have any videos or tech tips, you can tag me with them, post them in the HVAC School FB group or email them to bryan@hvacrschool.com.

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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.

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