#electrical

Tech Tips:

Grounding is an area of many myths and legends in both the electrical and HVAC fields. This is a short article, and we will briefly cover only a few common myths. For a more detailed explanation, I advise subscribing to Mike Holt's YouTube Channel HERE. Myth – Current Goes to Ground Actually, current (electrons) will […]

Start Capacitor & Inrush, Facts & Myths – Part #4

Now is the part where we get specific about start capacitors and inrush. If you haven't read the first three parts, please do so before reading this one, or it may not make sense. (You can find Part #1, Part #2, and Part #3 at these links.) I'm going to come out and say it […]

Commercial Contactor Considerations

This tip was created by Jason Pinzak and originally posted on the HVAC Technician's Facebook group. It is reposted here with permission from Jason. Thanks! Contactors are useful in commercial and industrial applications, particularly for controlling large lighting loads and motors. One of their hallmarks is reliability. However, like any other device, they are not […]

Multimeter Categories

Testo 760 Category IV Multimeter I was standing at a booth at the HVAC Excellence Educators conference, and an instructor walks up, grabs a meter, and asks me, “What's the difference between a category 3 and a category 4 meter?” Well, I really wasn't sure, but I knew that the category 4 meter is rated […]

You’re Grounded

One of the most common questions we get from techs is about using a voltmeter to diagnose a high voltage circuit. It's especially tricky when a tech is used to working on a low-voltage or 120V circuit, where there is a clear “hot” side of the circuit and a clear “grounded” side of the circuit. […]

Ohm My

One of the most common mistakes I hear techs make is confusing zero ohms with infinite ohms. The fuse above is showing near-zero ohms, which indicates a good electrical path with very little resistance. If there is a perfect path, it would have zero ohms (which isn't actually possible unless you happen to be […]

Something You May Want to Consider on Every Call

There are a few important things that I suggest checking on every service call to reduce callbacks and increase customer satisfaction. One of them that often gets missed is preventing wire rub-outs. One of my area managers and experienced tech Jesse Claerbout shot a video showing the simple step he takes to prevent major damage. […]

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In this short Q&A podcast episode, Bryan answers a listener-submitted question about superheat, including what it is and how we measure it.

Superheat is the number of degrees a refrigerant is above its saturation point. The saturation point is where you will have a liquid-vapor mix, so superheat only exists when a substance is a vapor. Saturated refrigerant should only exist in the evaporator and condenser, during which it is being boiled or condensed.

We usually measure superheat at the evaporator coil outlet and compressor inlet. The superheat at the evaporator outlet is usually around 5-14 degrees Fahrenheit, and it’s often between 10 and 20 degrees at the compressor inlet (compressor superheat). However, many systems try to get lower superheat values, and some manufacturers may require higher superheat values at the compressor inlet to prevent liquid refrigerant from getting into the compressor. Accumulators can help keep liquid refrigerant out of the system as well. We may also measure superheat coming out of the compressor on the discharge line (discharge superheat); this superheat may exceed 100 degrees Fahrenheit. Discharge superheat can let you know if the compressor is overheating the oil and causing breakdown or carbonization.

We use superheat to set the charge for fixed-orifice metering devices (as opposed to subcooling for TXVs), as superheat is a measure of how well we’re feeding our evaporator coil. When the system is off, the superheat will be 0. A system will equalize, and the refrigerant will be at saturation when that happens.

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