Month: October 2016

infrared_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

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


 


First let’s talk about what a noncondensable gas is. 

Any gas that does not condense (change from vapor to liquid) under the normal compression refrigeration conditions is called a noncondensable gas or NCG. These would commonly be air, nitrogen, carbon dioxide, Argon and Oxygen.

Noncondensable is the system will result in high head / condensing temperature and occasionally high side pressure fluctuations as well as decreased cooling capacity and efficiency.

The only way to remove non-condensibles reliably is to recover the entire charge and recharge with virgin refrigerant. You can’t remove noncondensables with a line drier and while you do remove air with a vacuum pump you only remove the air that entered the system once you open it. The vaccuum does nothing for the refrigerant the already pumped down or recovered as the non-condensables remain mixed with the refrigerant unless you are dealing with large volumes where they can actually be separated and the NCG’s removed.

However….

Noncondensables is often a term used by techs to mean ANYTHING in the refrigerant that shouldn’t be there, such as moisture, solid contaminants and other refrigerants.

Carbon buildup from brazing is a solid contaminant, not a noncondensable. Moisture in the system is moisture in the system, not a noncondensable. A mixed refrigerant (such as R410a) charged in vapor instead of liquid is a fractionated charge…. not noncondensables

I think you get the point

–Bryan


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


First off I want to thank Ulises Palacios for taking these photos. He is in the habit of cutting open the compressors he replaces to see why they failed (when possible). I think that’s pretty boss.

So why would the compressor have copper plating on the inside? They certainly are not manufactured that way.

The short answer is the acid inside the system eats away at the copper and brass components in the system. The copper is then deposited in the high pressure / temperature environment of the compressor.

Why does this happen?

The presence of any acids in the system can cause this to occur but the most likely causes are the combination of air and moisture reacting with the refrigerant oil (most prevalently POE) to create an environment in which the copper is dissolved internally and redeposited on the steel in the compressor.

The result inside the compressor is reduced clearances and ultimately locking, overheating and even short circuits if the mechanical failure results in winding damage as is fairly common.

So for a technician, what we can do in ensure we are properly evacuating the system and installing appropriate filter driers to reduce or eliminate the presence of air and moisture.

— Bryan

P.S. – For an in depth analysis of a study on copper plating in compressors you can read here

 

Yesterday I had a tech who was having some trouble finding a 35 PSI make on fall pressure switch. In the catalog one adjustable switch said (SPDT) but he didn’t quite understand what that meant. In that case it means single pole, double throw, and the “double throw” part means that the switch has terminals in both the close on rise and close on fall directions. Another common example of this sort of switch is a “3-way” light switch.

A single pole, single throw (SPST) switch is like a typical light switch. It only has one path (pole) and it is only closed or open.

A double pole singe throw (DPST) switch that is quite common is a 2-pole contactor. It has two switches but they only open and close in one direction.

A common double pole, double throw (DPDT) switch in HVACR is the 90-340 relay (and many other relays), where it has two circuits and they alternate between closed and open terminals.

— Bryan

switches

 

 

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