# Month: October 2016

## Infared Thermometers.. Yuck!

There are three reasons why I don’t like infrared thermometers for most HVAC tasks.

#1 – The Laser is Misleading
The laser dot is just a point of reference, not an exact point where it is reading. Often the thermometer will read lower, higher or over a MUCH wider area. Unless you are right up on what you are measuring you can’t be sure the result you are getting is correct.

#2 – They Only Read Surfaces
An infrared reads surface temp only, not air temp . This is necessarily a problem, but “shooting a vent” is not the same as measuring the air temperature coming out of it.

#3 – They Can be VERY Inaccurate
Infrared thermometers are only accurate on surface that have high “emmisivity”. These are things usually soft or porous surfaces like meat, or carpet or drywall. Metals have a low emmisity which means that if you are reading a pipe an infrared could read much lower than the correct temperature.

Infrared thermometers can be useful to do comparisons where reading the correct temperature is less important than comparing one spot to another, such as looking for hot spots in a panel, or checking a zone to see if a damper is open.

So long as you use the right tool for the job you should be fine, but in general….

I don’t like infrared thermometers.

— Bryan

P.S. – While I don’t like infrared, I REALLY like thermal imaging. Check out these nice products from FLIR – hvacschool.com/flir

## Basic Electrical Theory

1. According to Ohm’s Law, increasing resistance in a circuit

Question 1 of 10

2. A 5KW heatstrip rated at 230V would draw how many amps at 23V?

Question 2 of 10

3. Electrons contain a _________ Charge

Question 3 of 10

4. Atoms with _______ electrons in the outer layer (Valance) generally make better Insulators

Question 4 of 10

5. Volts X Amps = ________

Question 5 of 10

6. A common example of an inductive load is

Question 6 of 10

7. 1 Volt is

Question 7 of 10

8. A _________ is an example of a switch

Question 8 of 10

9. 1 HP = _______ BTUs per Hr

Question 9 of 10

10. When you install a dimmer on a incandescent light bulb and add resistance to the circuit the light will dim and the amperage of the circuit will decrease.

Question 10 of 10

## Switch voltage

Remember. On a powered circuit you will read voltage across an OPEN switch not across a CLOSED switch.

Both sides of a closed switch are electrically identical.

— Bryan

## Control Voltage Overamp – The Less Usual Cause

In most cases when a LV circuit is blowing a fuse it’s because one of the circuits is shorted to ground or common. Rubbed out wires, shorted components and boards etc….

But less commonly you will see the LV circuit draw high amps because of magnetic solenoids that are energized but  the mechanical pin, stem or armature is stuck.

A common example is a contactor that is stuck open. This results in high amperage because the solenoid is energized without the magnetic resistance (reactance) provided by the induced magnetic field.

Another example is a reversing valve solenoid that is not mounted or is not properly on the reversing valve stem.

You can see the same effect in any magnetic switch gear such as relays, pump down solenoids etc…

So check for short circuits first but also keep your eyes open for stuck or improperly mounted solenoids.

–Bryan

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