Month: August 2017

Oil pressure controls… Oil failure controls…  Oil safety controls…   They’re a pain in the neck when they trip and diagnosing those problems can really tax even the best of techs.

 

As semi-hermetic compressors get larger, they can no longer rely on simple splash or “sling” type lubrication strategies where oil is just flung around inside the compressor and that is sufficient to provide lubrication.   Once we cross that threshold, we need an oil pump to force oil through ‘galleys’ machined into the crankshaft to lubricate all of the bearings.   To ensure that the compressor has adequate lubrication at all times, manufacturers require a safety control to prove there is sufficient oil pressure and shut the compressor off if there is not.

 

An oil pressure control is, effectively, a differential pressure control with a built in time delay.

 

HUH?

 

Let’s look a little closer.

 

First thing we have to do is look at how we measure oil pressure.   The oil that we’re pumping through a compressor starts in the crankcase, so it’s already under a certain amount of pressure, depending on the suction pressure of the system.  That suction pressure affects the output pressure of the pump.  To properly measure oil pressure, we can’t just look at the pump outlet pressure, we have to look at the pump outlet pressure MINUS the crankcase pressure. This is called NET oil pressure.

 

Measuring crankcase pressure rather than just measuring suction pressure will become important later when we get into troubleshooting.  This is why the oil pressure control has 2 pressure ports and is measuring the differential between those 2 pressures.  The pressure control has a time delay because, on startup, the system needs a period of time to stabilize.  This time delay is usually fixed at 90 or 120 second, depending on the manufacturer and the brand and type of control.

 

Most new controls are electronic, but there are still a lot of mechanical controls out there, so let’s talk about how they work and, once we have a solid understanding of mechanical controls, the electronic ones are pretty easy to understand.

 

The first thing to understand about oil failure controls is that they require a minimum of 3 wires. They’re more than just a pressure control, remember…

 

So, we’ve got line voltage going to the control AND we’ve got 2 wires for the control circuit. Typically, you’re going to see terminals “2” and “M” jumpered together so everything I say assumes they are connected electrically.   Some rare applications will require them to not be jumpered but that’s beyond our scope here.

 

Depending on our control voltage, we’ve got line voltage at V1 or V2, one leg of the control circuit at M and one at L.  It’s very important to understand that L also acts as both one leg of the control circuit AND the second leg of the circuit for the heater (H) in the control itself.  This means that, unlike most other controls, we have to be careful where we put this control because the leg from L cannot have any other switches in it.  This requirement will be made clear in the paperwork included in the control and now you understand WHY.

 

Now, let’s look at the switch in the control labeled PC.  This switch, pictured as normally closed, will OPEN when there is sufficient pressure differential.  So, when we start the compressor, power is applied to V1 (or to V) and once oil pressure builds up to the 9-12 PSIG range, it will open switch PC and de-energize the heater.

 

Now, if this switch(PC)  is closed and the control is energized (power to V1 or V2) then the heater H is energized.   Once that heater reaches a certain temperature, switch TD, which is a thermal type switch similar to the one found in an electric heat sequencer, will open, breaking the control circuit.

 

This may seem complicated, but really stop and take the time to understand this.   You’re not really going to be putting a meter across switch PC, it kind of just works in the background, you just need to understand that it’s there and what it does to make the control function.

 

Electronic controls integrate these functions into an electronic control board and a small differential pressure switch that screws into the oil pump on the compressor.  They still have the same basic wiring requirements, having to have the third wire for power and an uninterrupted wire from L to the load.  The time delay feature is electronic rather than thermal, but there is still a small differential switch to monitor the net oil pressure.

 

In operation, an electronic oil failure control works pretty similar to the mechanical.   Power on the line voltage terminal and L supply the PCB (Printed Circuit Board) with power while M and L act as the control circuit.   The PCB monitors the differential pressure switch.  This is typically a brass assembly threaded directly into the oil pump.   If oil pressure drops too low, this time, the differential switch will typically open, signalling the PCB to begin the timing that was handled by the heater in the mechanical control.

 

Electronics have some advantages over mechanical controls.   More accurate timing being first among those.   A thermal switch is somewhat dependent on its environment.   The same switch in a warm ambient is going to time out faster than it would in a colder ambient.   With electronics, timing is repeatable across a wide range of ambient temperatures.

 

Moving into the future​.

As electronic controls advance, manufacturers are integrating more features into them.  What was once a single purpose control  monitoring the compressor’s oil pressure is now turning into what amounts to a central control unit, taking oil pressure input along with motor current data, high and low pressure switch inputs, motor temperature inputs and acting as an integrated safety for the machine.   Not only does it provide troubleshooting data to the tech in the form of error codes, some are acting as data recorders allowing more detailed troubleshooting if the tech connects to the controller with a laptop or other device and downloads the data.

— Jeremy Smith CM

 

 

This article was written by Gary McCreadie from “HVAC know it all”. You can learn more about Gary and his tips and growing community on Facebook and on LinkedIn


What is an economizer?  Simply put, it is a mechanical device that is designed to reduce the consumption of energy, whether it be fuel, electricity, or other. According to Wikipedia, the first economizer was patented by Edward Green in 1845.  It was used to increase the efficiency of stationary steam boilers.

This article will revolve around air side economizers.  You will typically see them as an accessory built into rooftop units used for the purpose of “free cooling”.  Free cooling is a funny term because it’s not actually “free”, the fan motor and economizer controls must be powered in order to operate, which consumes energy.  The term merely demonstrates the fact that less power consumption is taking place due to the fact we are utilizing outdoor air to cool a space rather than the use of a compressor or compressors.  Economizers also offer the added feature of providing fresh air to the building and it’s occupants.  A carbon dioxide sensor can be integrated into the set up.  As CO2 levels increase within the building, the outdoor air dampers are commanded to open, filling the space with fresh air.  As CO2 levels drop off, the dampers return to their minimum position.
The Guts of an Economizer
The economizer set up employs several parts in order to operate correctly.
1) A set of outdoor air dampers that are directly linked to the return air dampers are used to control air flow.  They move together as one, as the outdoor air dampers begin to open, the return air dampers begin to close and vice versa.
2) An outdoor air sensor.  This sensor is responsible for determining if the outdoor air is acceptable for free cooling.  In most cases, there will be an option between a sensible temperature sensor or an enthalpy sensor.
Sensible Temp Sensor – Measures dry bulb temperature of the air
Enthalpy Sensor –  Measures heat content within the air measured in btu/lb.  This sensor takes dry bulb temperature and wet bulb temperature into account for total heat content.
3) An indoor air sensor, this sensor reads sensible temperature and is responsible for maintaining mixed or discharge air temperature.  The damper assembly will modulate according to feed back from this sensor to maintain a pre-determined mixed or discharge air set point.  On newer economizer controls, like the Honeywell Jade for example, you are able to set the mixed or discharge air temperature as desired.
4) The damper actuator, which receives a signal from the economizer control board and moves to the assigned position to maintain the mixed air or discharge air set point.
5) When using free cooling you must remember that you are introducing fresh air, this added air into the space can cause positive pressure issues within a building.  To eleviate this problem economizers in most cases will have a built-in barometric relief damper or power exhaust system.
6) The control board is the heart and soul of the operation.  The control board receives sensor input signals, internally calculates the next step and relays the output signals to the damper actuator and power exhaust motor if utilized.
Order of operation
To keep it simple, the following example will be based on a single stage cooling rooftop unit complete with an economizer package.
On a call for cooling from the thermostat or BAS (building automation system), the Y1 terminal will be powered.  In most cases, the signal will first move through the rooftop control board and over to the econmizer control.  At that point, the econmizer control will then decide whether to proceed with free cooling or mechanical cooling based upon the outdoor air conditions either using sensible temperature of the air or the heat content of the air measured in enthalpy.  If the outdoor air is not suitable for free cooling, the control signal will be then relayed back to the main control board of the rooftop and initiate mechanical cooling (compressor operation).  If the outdoor air is suitable for free cooling, the outdoor air dampers will modulate from their minimum position (damper minimum position is set up during commissioning to maintain constant fresh air to the building and occupants) to maintain the mixed air or discharge air set point until the space temperature is reached.  Once the thermostat or BAS has been satisfied, the call for cooling will cease.
Most air side economizers in general, work as explained above.  It is best to contact the manufacturer of the equipment you are working on for technical advice or when issues pertaining to that system arise.
— Gary McCreadie

Adolfo Wurts from Arbiter Incorporated, designer of the UEI WRS line of Bluetooth scales comes on the podcast and we talk about scales including.

  • When to pull a scale off of the truck
  • Opportunities you may be missing to be a better diagnositician
  • Features of a good scale
  • All about the industry leading WRS110 and WRS220 from UEI

You can find these scales for sale at TruTech Tools by going HERE

And don’t forget to use the coupon code “getschooled” for an 8% discount at Trutechtools.com

Find out more about the WRS line by visiting the UEI website 

Testo 557 vacuum gauge and Appion core removal tools shown

I’ve had a change of heart.

Back in the early 2000’s during the big construction boom I did a lot of system startups on residential units for a large company I worked for.

When installers were running the linesets prior to startup they weren’t always very careful to keep them clean and dry and many times we would end up with a restriction in the piston or TXV.

These new residential systems come with a precharged with refrigerant in the condenser. So after my vacuum was complete I would “release” the charge by slowly opening the liquid line service and watching to see if my suction pressure would steadily rise.

I did this so if there was anything in the liquid line it would hit the screen or drier before the metering device instead of possibly running the other way and clogging the TXV or orifice.

Many times I would know that there was a restriction before I even started the system because I got used to watching that suction needle rise. While I did this for a good reason that reason is in the past.

When we install systems we take great care to make sure the lineset stays clean and dry and we flow nitrogen while brazing with the line drier installed near the indoor coil.

It’s a new day and I’m giving up my old sins.


So now I must admit… the better way to do it is to slowly open the SUCTION valve first. This prevents oil loss out of the compressor into the discharge line and out of the liquid line.

It is not likely that you will lose enough compressor oil to cause any damage by opening the liquid line slowly, but any oil the compressor does lose has a long journey before it gets back to the compressor. The other issue is that oil loss in those first few moments in the life of a new system can have long lasting effects on the operation and longevity of that compressor.

Have you ever taken a liquid line hose off after a new system install and gotten oil all over?

The reason for that is often due to opening the liquid line first and the compressor losing oil to the discharge line and then to the liquid line.

When you open the suction side slowly first and oil loss from the compressor will enter the suction line. Once the compressor begins running no it will pull that oil back into the compressor.


When doing it this way you would attach your micron gauge to the liquid line core remover side port with the schrader in place in the side port. Once you completed your vacuum and proved you had no leaks or moisture by valving  off the VCT’s and watching your decay rate. You would then attach your gauge manifold and slowly crack the suction side until you see a few psi on the liquid side. Now remove the vacuum gauge to ensure it is not damaged by the system pressure.

Most micron gauges can handle some pressure, for example the Testo 552 can handle up to 72 PSIG(4.96 bar) and many can handle 400 psi(27.57 bar) or more. it never hurts to remove that expensive and sensitive micron gauge before you expose the sensor to high pressure, but never remove it BEFORE the system is under positive pressure or you will lose the entire vacuum.

You would then purge your manifold hoses and fully open the suction valve and then the liquid line valve.

When charging a system that has no charge (not running) weigh refrigerant into the liquid line first until both sides equalize in pressure to ensure that you are not introducing liquid refrigerant right into the compressor crankcase.

Also keep in mind that running the crankcase heater once the charge has been released and before the system is started is also a good practice to prevent flooded start on the compressor.

— Bryan

Service factor is an interesting motor rating that you will see on many motor data tags. It simply means how much additional “work” a motor can do or “load” it may be placed under for short periods of time without failure or overload.

For example. The FLA or Full Load Amps of the motor above is 10.8 amps at 115 volts

The Service Factor or S.F. is 1.5, which makes the Service Factor Amps 16.2 (rounded down to 16 on the motor tag) because 10.8 x 1.5 = 16.2

Don’t confuse SFA with LRA (Locked Rotor Amps). LRA is the current the motor will draw when the rotor is stationary, such as during startup. Service Factor is simply a short term “fudge factor” that the motor has for short periods of higher than normal load.

When a motor is running above its Full Load Amps and in the Service Factor range it may function but its operational life will be shorter and it will generally run at lower efficiency and power factor.

— Bryan

I was about 13 years old the first time I bent EMT with my uncle. We were doing a renovation at a church, and watching him bend EMT and then getting to do it MYSELF was a truly religious experience.

There are a few things in the trade where workmanship really comes into play such as copper pipework, making up a panel or fabricating ductwork… bending EMT belongs on that list. While most commercial electricians do it every day, HVAC techs and installers only run into an application where we do it on a rare occasion. When that does happen its good to have a basic understanding of how it works. In this video Juan from the The Air Conditioning Guy channel goes over some quick basics on bending EMT

For more info you can read this great guide on bending from Klein

— Bryan

For those of you who follow the podcast you know how excited I am about the new MeasureQuick app and what it will do to help technicians make better measurements and diagnosis. The app is NOW AVAILABLE on Android and will be available within hours on IOS (Apple)

To find out more and to download just go to measurequick.com/downloadnow

Here is a video from Jim on the launch

And a video from Brad Hicks with HVAC in SC showing his system at home on the app

and you can hear the MeasureQuick launch podcast episode HERE

Big thanks to Jim Bergmann for bringing this excellent technology to the HVAC industry.

As a technician gains skill they will learn that regularly testing your tools is a huge part of success. It isn’t long in the field before techs find out that just because a meter or gauge gives a particular reading it doesn’t ALWAYS mean it is correct. Vacuum is one of these areas.

Everything in an air conditioning and refrigeration system leaks to some extent, our job isn’t to eliminate all leaks, our job is is to reduce the leakage rate to as low as possible. When using a sensitive micron gauge we find that isolating an assembly and checking the “decay” or standing leak rate is a great way to test and ensure that a system has minimal leaks and moisture. The challenge is that all of the connections in your rig leak and even the vacuum gauge itself leaks.

Some techs attempt to test the leak rate on micron gauge by connecting it to a core tool and then straight to the pump, evacuating the gauge down to very low level and then valving off. If you do this, you will find that every commercially available vacuum (micron) gauge shoots up pretty quickly. This is because the VOLUME of the gauge and coupler are so low that ANY leakage whatsoever has an enormous effect.

In this video Ulises Palacios shows us how to use an an empty recovery tank to better test the leak rate of a vacuum gauge rig.

It is certainly important to test all of your vacuum rig components, just remember that volume makes a huge difference when decay (standing vacuum) leak testing.

— Bryan

First off, the correct acronym for a GFI (Ground Fault Interrupter) is a GFCI (Ground Fault Circuit Interrupter) and the purpose is to act as a safety device to protect from electrical shock.

GFCIs can be built into outlets, circuit breakers and even extension cords and are generally used for safety in wet environments like bathrooms, kitchens and outside.

A GFCI measures the difference in current between the line (hot) and the neutral. When even a small difference exists between neutral and hot the GFCI trips. This happens because a difference between neutral and hot means that some of the current is “leaking” to ground instead of being carried properly on neutral.

An example would be an electric drill plugged into an outlet outside and the cord plug falls into a mud puddle. If there is no GFCI some of the current will go out of the plug to ground through the puddle, causing hot to carry more current than neutral and making the puddle a potential shock hazard. If the circuit were protected with a GFCI it would trip immediately when the imbalance was detected.

Another nice thing about a GFCI is that it can help protect a circuit that does not have an equipment ground such as tools and appliances with two prong cords or two conductor outlets.

— Bryan

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