Month: November 2017

This article serves two purposes. First, it is an article for technicians who have heard of the dreaded “ghost” voltage but never understood why it happens. Second, for my own apprentices and techs who I stumped this morning with a diagnosis problem that involved “ghost” voltage that they were unable to diagnose.

If they read my tech tips they will get the answer… sneaky right?

 So what is meant by ghost voltage?

In some cases, you will be diagnosing an electrical issue, usually controls / low voltage issue. You will be measuring potential on a circuit and then when the circuit is connected to the load the voltage will disappear … like a “ghost”.

For example, you make be measuring 24v at a condensing unit on the “Y” contactor circuit when the conductor (wire) is disconnected, but as soon as you connect it to the contactor/control board the voltage “disappears” when measured across the load (across the contactor coil) or more simply from Y to C.

In other cases the voltage may not disappear completely, it may just drop way down, or in other cases the contactor may chatter, circuit board lights dim etc…

I have heard all of these situations called “ghost” Voltage, but they are actually just voltage drop and these symptoms are caused by additional resistance in the circuit OTHER than the designed load.

Quick Note: there are also “induced” voltages that can appear as ghost voltage due to conductors running in parallel with other current carrying conductors. This is more common in Commercial and industrial applications where many wires are bundled or in close proximity over long distances. These charges are usually small and often “disappear” under load.

Rarely do we want more than one electrical load (resistance point) in a single circuit. When this does occur it is usually undesigned and caused by of long wire lengths, improperly sized wire and poor connections.

Now to CLARIFY, when referring to a circuit we mean one complete path between electrically different points (say L1 and L2 in single phase 240 or 24v hot to 24v common on a control transformer). Some think of parallel circuits as a single circuit, but while they may share conductors they have an individual load path.

To cut to the chase, whenever wire is undersized, runs of wire are too long or the circuit contains poor connections there will be additional resistance introduced to the circuit. When there is more resistance added in places other than the load (in this case a contactor coil) there will be a voltage drop and therefore the voltage applied to the load will be decreased. When a wire isn’t connected to the load this drop will be invisible because the load isn’t in the circuit and therefore you are simply reading across the OTHER, unintended load (resistance) which will often be the full voltage depending upon the exact issue and when you are making the measurement.

In every complete and independent circuit, including a series circuit, the amperage is the same no matter where in the circuit you measure it. Before the load, between loads, after the loads… it doesn’t matter. The amperage is dictated by the total applied voltage and the resistance (or more accurately the impedance) of the entire circuit.

The voltage applied to each load is dependant on the resistance of the load in comparison to the total resistance of the circuit. In the example below, you can see that the amperage is the same on each load and is dictated to be 500 microamps because the total circuit ohms is 18,000.

The voltage drop of each load in series is equal to it’s percentage of the total circuit resistance. Since  loadR1 is 16.5% of the total resistance in the circuit, the voltage drop across R1 is 1.5V because 1.5 is 16.5% (0.165) of 9V.

There are a few other factors that make the trouble with voltage drop worse. Let’s say you use an undersized wire to feed a lightbulb, an undersized wire means that the conductor has a lower ampacity (amp capacity) than it should have. Once the circuit is energized the wire will begin to heat up, as it heats up the molecules in the wire begin moving faster which increases the resistance of the wire. The greater the resistance of the wire the greater the voltage drop across the wire resulting in a hot, dangerous wire, increased voltage drop at the bulb, less light from the bulb and decreased circuit amperage (less total work being accomplished).

In the case of many loads including inductive (magnetic) loads like a compressor contactor, the resistance in the coil isn’t just resistance you can measure with the contactor de-energized. This resistance that is created within an electromagnet once it is energized is called “inductive reactance” and it is measured in ohms of impedance. In order for the contactor coil to properly engage it requires the correct applied voltage and without the properly applied voltage, the resistance of the coil remains low. The crudely drawn diagram below (I’m no artist) shows a contactor coil circuit with no issues and a 0.5 amp  current at 48 ohms

When you add in a 200 ohm “bad connection” or any other type of resistance, not only does it create huge voltage drop, it also drops the impedance of the contactor coil itself with the result being a very low applied voltage (3.13V) on the contactor coil with it connected and under load. Under these conditions, the contactor won’t try to pull in at all. Under less extreme conditions it may chatter or become noisy.

Now, this is a hypothetical situation, but you will notice that the poor connection is AFTER the contactor coil in what we call the common circuit in 24v controls. It doesn’t matter WHERE in the circuit resistance is added, whether before the switch (in this case a thermostat) in the line side or after the switch on the load side. It could even be in common or in the switch itself.

Anytime additional resistance is added to a circuit it results in voltage drop when the circuit is intact. When we disconnect wires to test voltage or test voltage with a circuit that has an open switch we can create confusion and observe “ghost” voltage. In reality it is simply extreme voltage drop caused by additional resistance in series with the load.

— Bryan

carrier_defrost_thermostat

When you work on a heat pump system and you want to test defrost there are so many different test procedures to follow to test the board and sensors. Most involve “forcing” a defrost by shorting out pins on the board or advancing the time on the defrost initiation and installing a factory provided pin jumper.

Lots of pins and jumping involved.

But one thing to need to be able to distinguish is whether the system uses sensors or thermostats to initiate and terminate defrost.

A thermostat is an open and closed switch, they are usually round in shape like the one shown above and they open within a set temp range and they close within a set temp range. The one shown above is a Carrier Defrost Thermostat and it closes at 30 degrees +/- 3 degrees and it opens at 65 degrees +/- 5 degrees. In this case because this particular sensor closes in colder than 32 degree temps you can’t even use an ice bath to test it. If it is below 32 outside it is easy to test (duh) otherwise you can just run it in heat mode with the cond fan off and see when it closes by using an Ohmmeter.

On a defrost thermostat you can also easily jump it out to test the board since it is just open an closed.

A defrost sensor is a thermistor. A thermistor changes resistance based on the temperature it is exposed to. In order to test you can measure the ambient temperature, make the the sensor is removed and acclimated, measure the Ohms  of resistance and compare to the manufacturer chart.

Thermistor

You CANNOT jump out a thermistor.

— Bryan

P.S. – A podcast about Heat pumps is available HERE

We’ve all been new at one time or another so there is no need to get all judgy about some of the mistakes new techs make just because they are inexperienced.

However…..

These are some very preventable mistakes that occur due to simple oversight and carelessness that need to happen 0% of the time.

Caps and Seals

Leaving caps off is never OK. While it’s true that Schrader valves and back seating service valves “should” seal completely and shouldn’t be left leaking it is always possible that a little leakage can happen. Besides, keeping bugs and dirt out of the ports is reason enough to keep the caps on.

Bill Johnson (co-author of RACT) made a really good point on a recent podcast. When a system is apparently low (which you can verify through non-invasive temperature tests) you shouldn’t just pull off the caps and attach the gauges. First, look for oil at the ports and leak check them to eliminate port leaks as a possible cause. Once you remove the caps and attach your manifold you won’t be able to know if the ports were a leak point or not.

Every time I remove caps I look inside them to make sure they are in place unless it is a flare hex cap that doesn’t require a seal.

It’s a good practice to keep all caps and screws together and in the same place on every call. This helps to ensure they don’t get accidentally knocked into the dirt, lost or forgotten.  Put those caps back on, finger tight for caps with seals and snugged up with a wrench for hex flare caps (Trane residential units for example).

Leaving Disconnects Out / Off

Obviously, nobody TRIES to forget the disconnect but it still happens all the time and it’s almost always because the tech gets in a hurry or distracted and usually both, and it can be eliminated easily by some best practices.

Most often the disconnect is left off or out during maintenance or during very simple repairs. This is because the tech will often run test the equipment, then perform the maintenance or minor repair and leave without run testing again. This order of test first then clean / repair isn’t my favorite for several reasons will silly mistakes being one of them.

I advocate for performing the comprehensive run test at the very end of a repair or maintenance meaning you are observing the system running right before you leave with the last action being resetting the thermostat or controls back to the desired setpoint. When you run test last you don’t forget silly things that prevent the system from running.

Always do a final walk of the job before leaving and check disconnects, setpoints, cleanup and check for tools.

Making Poor Electrical Connections 

I see it all the time. Capacitors tested and the spade connections left loose, contactor lugs not properly torqued, stranded wires with some of the strands cut off to make the wire fit, crimp connections on solid wire…. the list goes on and on. Here are the top mistakes to avoid.

  • When forcing on a female spade (on a capacitor for example) it should be very snug. If it is loose at all, pull it off and pinch down the spade sides a bit to ensure it’s a snug fit
  • When making a crimp connection only do so on a stranded wire and use an appropriately sized connector. Position the jaws so that the indent crimp is made on the side of the connector OPPOSITE the split in the barrel.
  • Never cut strands of wire to make a conductor fit under a lug. Use the proper connection (termination) type for the conductor.
  • Never leave exposed wire, strip back insulation only to the length required to make the connection and no more.
  • Don’t leave connections under tension. Use straps and zip ties to keep tension away from connections so that they aren’t left under a pulling/disconnecting force.
  • Make appropriate connections for the job, never leave connections open to the environment unless they are rated for it.

When making any electrical connection always pull the connection to make sure it is a snug fit before walking away.

Failing to See the Obvious 

So much is made of good workmanship (how things look) and diagnosis (figuring out what’s wrong) and rightfully so. However, for a new tech, nobody expects you to do the best looking work out there or to diagnosis the super difficult situation. You are expected to use common sense and spot things that are out of the ordinary or that can lead to issues. Here is a quick list of things to look out for that you can see with little to no experience.

  • Look for refrigerant oil stains, often oil stains or residue can lead you straight a refrigerant leak.
  • Use a mirror and a flashlight and look for dirty evaporator coils and blower wheels. You may make a diagnosis but if you leave the system with a dirty coil or a blower wheel you still look silly.
  • Check the air filter and let the customer know you checked it. A home or business owner may not know much about HVAC but they know what an air filter is and reporting the condition back helps give them confidence.
  • Watch for rub outs on copper lines, feeder tubes, external equalizers and sensing bulbs and wires. You can often find or prevent a problem just by looking for areas of contact between tubes and/or wires.
  • Inspect control wiring for cuts or UV damage outside. If the weedwhacker doesn’t get the wire often the sun will.
  • Look for past workmanship that may be done incorrectly. Just because that fan motor or capacitor is new doesn’t mean it is the right size and wired properly. Always double check your own work as well as work done by others.
  • Before making a repair double check the previous diagnosis and check that the part you have is actually the correct part. There is NOTHING worse than removing a compressor t find out the one you have isn’t the correct one. ALWAYS double check the diagnosis and the part.

There are many other things that could be added to the list, but for a new tech if you do the following you will be on the road to success even if you are green.

  • Read product manuals and never stop learning
  • Listen carefully to senior techs and ask lots of questions
  • Help other techs when they are in a pinch
  • Smile and treat customers with respect
  • Compete with yourself to do each job better than the last
  • Walk  every job before you leave to make sure everything is buttoned up (Screws, caps, disconnects)
  • Ask every customer is you have done everything to their satisfaction and if there is anything you can improve.
  • Do all the little things with exceptional detail. Cleaning drains, washing condensers etc… always do it with a level of detail that exceeds your peers and you will build a reputation for excellence.

If you do these things your co-workers, customers, and managers will generally overlook the mistakes you make just because you are green.

— Bryan


We’ve seen it before.

A tech diagnoses a failed blower relay or board so they leave the blower jumped out by putting a terminal multiplier on the common terminal of the relay / board and connecting the fan speed tap right to power.

There can be an issue with that.

Some electric heat fan coils have a heat / blower interlock where the heat relay / sequencer back feeds and brings on the blower across normally closed (NC) contacts. The purpose of this is to ensure the blower comes on with a heat call without the need for a G call.

In some circumstances when you put in a terminal multiplier and constant power the blower, the G call sends that constant power back to the Heat strips and brings them on.

Not good… high power bills, melted wires, fire, death and stale doughnuts.

So, if you are leaving a blower jumpered out to run constantly I advise doing it separate from the board completely.

Coincidentally the photo at the top is a setup that will not back feed because it uses two isolated circuits on the Heat sequencer for fan and heat…. so the photo I chose wasn’t the best. Cut me some slack, the blower assembly was sitting right behind my office.

— Bryan

This topic came up because I was testing out the new MR45 digital recovery machine and that machine goes off by itself when it hits a 20″ Hg vacuum. This is a cool feature but it is good to know when that level of vacuum is overkill and when it’s not enough according to EPA requirements.

Why would you need to recover into a vacuum you might ask? Well, so long as you are above a PERFECT VACUUM (and you always do) there are still molecules of refrigerant in a system even at 0 pisg (14.7 PSIA at sea level). In low pressure systems like centrifugal  chillers the entire system charge can often be in a vacuum when the system is off, this means that recovery on these systems means you START below 0 PSIG and go down from there. 

First off let’s pretty much assume that none of you are using recovery machines OLDER than 1993 so really only look at the right side of the chart above.

If you are working on an air conditioning system with UNDER 200 lbs you are safe taking your recovery to 0 or atmospheric pressure. If the system you are working on has OVER 200 lbs of refrigerant or if you are working on a medium pressure or low pressure system you will need to pull the system into a vacuum.

The EPA does make an exception if the system has a know leak and pulling into a vacuum will result in contamination of the recovered refrigerant. Here is an excert from the EPA final rule summary from 1995 (still in force)

Also let me clarify that 25mm hg absolute is another way of saying 25 torr or 25,000 microns, it’s just a finer scale and it goes from 760 torr (760,000 microns) down as the vacuum gets deeper whereas inches of mercury (“hg) goes up as the vacuum gets deeper.

— Bryan

There are several types of Ice Machines but in this article we will focus on Cuber style and Flaker or Nugget style. Both types produce Ice but the process of freezing and harvesting is a little different. The application in which the Ice will be used will determine what style of machine is needed. I primarily work with Restaurants and Hospitals so my article will be geared in that direction.

Let’s start by simplifying the ice making process, if we take water and circulate it over an evaporator that is below freezing we will at some point start to freeze that water, once our Ice has formed we than harvest the ice and start our process again. That’s about as simple as it gets

The  steps to make Ice seem simple take water and freeze it, but It’s not that simple. Making Ice cubes is actually a pretty complicated process, with several critical steps that must be met for the process to work correctly. The first step starts with properly cleaning the water that will be made into ice to remove any impurities, water itself naturally contains minerals and those minerals are an Ice Machines worst enemy. The minerals lead to calcium buildup which causes issues with the ice machine. A quality ice machine install will have a high quality water filter system installed that was sized properly and has the appropriate filters inside that are chosen after a water quality test has been performed. Once we have properly filtered water we bring the water into a reservoir inside the machine and the water waits until the machine is ready to make Ice.

Among all the ice machine manufacturers there are several methods that the machine will tell itself that the ice storage bin is low on Ice and to turn on, the most common methods are a thermostat and or some sort of mechanical control that is actuated by ice buildup, subsequently telling the machine that the ice is low and it’s time to turn on.

Cuber style ice machines

Assuming the machine is ready to turn on, most brands of ice machines will start in a pre-chill, which means we cool the evaporator with no water running over it, this is done to try and prevent slush from forming. Than by means of a water pump the machine will start to circulate the water over the evaporator, and that water will continually run over the evaporator and down into the sump than it will be pumped over the evaporator again, each time it passes over the evaporator the water will get colder and colder and eventually a little bit of the water will start to freeze to the evaporator plate, this process will continue over and over again until the ice is the proper thickness. The thickness can be determined by many methods including a thickness sensor, water level monitoring, and or a timer. Once it’s time to harvest the ice the most popular method is to introduce hot refrigerant from the discharge of the compressor into the evaporator and subsequently melt the ice off the evaporator from the inside out while running a little bit of water over the cubes to assist dropping the cubes off the evaporator. The harvest cycle is usually terminated by a timer that is in the circuit board. Each manufacturer has their own unique way of making and harvesting the ice. With all cuber style ice machines the harvest cycle is very dependent on maintaining an adequate high side pressure as their defrost depends entirely on it. When the machine is self contained and located indoors its not too hard to maintain the proper head pressure because the building will likely be conditioned, however on remote systems where the condenser is located outside we utilize head pressure control valves (headmasters) to back up the refrigerant in the condenser to reduce the condensing capacity of the condenser and subsequently raise the head pressure.

Flaker or Nugget style Ice machines

These machines have a unique way of making ice they utilize a round cylinder evaporator that has an auger inside of it that is turned by a high torque gear motor. The auger sits directly In the center of the evaporator with less than 1/16th of an inch clearance on either sides and the auger is always spinning it has the shape of a corkscrew. The machine will have a water reservoir that supplies water to the evaporator whenever it gets low. The machine will start to freeze the water and as it becomes ice the continually turning auger will force the ice up to the top of the evaporator and out of a nozzle that will shape the ice into the desired style (Crushed, Flaked, and or Nugget). It is important to notice that with this style of ice machine the harvest cycle happens when the ice gets thick enough for the auger to scrape it off and it both freezes and harvests the ice at the same time.

— Chris Stephens

P.S. – we have a new podcast out on ice machines HERE enjoy

My Grandfather is a really interesting guy. He grew up working in the Pennsylvania coal mines starting at the age of 7 or 8 and then worked as well driller, and a plumber, also went to HVAC school, and did some gas work worked a while as an electrician, welder, diver and ended up as an aircraft salvage man.

One of his favorite phrases is to call adjustable wrenches and channel locks (slip groove or tongue and groove pliers) “shoemakers tools”. I literally have no idea WHY he would call them that, or why he thought it was so funny to call them that but he certainly didn’t mean it as a compliment.

It is usually best to use a properly sized socket or wrench to do a job rather than reaching for a “multi-purpose” wrench, but every tool has a purpose and if you are going to use a tool it’s best to use it properly. I know this is basic, but we cant assume everyone has a grandpa like mine.

Pull Don’t Push (When You Can)

Whenever possible orient the wrench so that you are pulling rather than pushing (Yes, I know I’m awkwardly pushing in the GIF below) . This is a much more smooth and natural motion and you will be able to apply more force.

Pipe Wrenches are Special

A pipe wrench is only for working with pipe, NOT nuts, and bolts. I know this should be obvious but I worked with a guy once who treated a pipe wrench like a regular wrench and left a lot of damaged bolt heads in his wake.

A pipe wrench has sharp, angled teeth that will grip in one direction and release in the other direction. Open the jaw wide enough that the pipe sits in about the center of the pipe wrench unlike a typical where the object to be turned sits all the way in the back of the jaws.

Keep in mind that a pipe wrench will leave marring on the surface of the pipe, if you don’t want it to be damaged you can use a leather (or even rubber) strap around the pipe to protect it before using the wrench. A leather belt can do the trick.

Turn the Wrench Toward the Bottom Jaw

Maybe there is an exception to the rule, but not in any of my wrenches. If you turn the wrench toward the bottom jaw they will grip properly and be less likely to slip. In order to tighten vs. loosen just flip the wrench over and turn the opposite direction

Righty Tighty is Annoying

Half my childhood was HAUNTED by the phrase righty tighty, lefty loosey. IT IS ROUND! there is no right or left unless it is a reference to another direction (the top). It’s better said as clockwise tighty… and yes, I know that doesn’t sound cool.

— Bryan

 

 

 

 

 

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