- Tech Tips
- Podcast Episodes
Every contractor is different, I get that. we don’t all need to do everything the same way or include the same services with repairs but there are some “best practices” that can save you a lot of heartache before, during and after you make a big repair.
Catch it During Diagnosis
Let’s say you find a failed, shorted compressor on a 7 year old system that still has manufacturer parts coverage. If you simply quote the compressor and leave you may be missing a lot of other maintenance related issues that can affect operation once the compressor is replaced. A short list of items to check would be –
And this is just for cooling side issues. If the system is a fuel-burning appliance you would inspect every part of the furnace operation as well.
Testing all of these things is commonplace AFTER a repair, but it makes so much more sense to do it beforehand so that you can either charge appropriately for any of these items that need to be addressed or let the customer know you are including them to differentiate you from the competition.
Things to Do Along With Major Repairs
There are a few things you need to do as a matter of course during major air conditioning or refrigeration repairs that just make good sense to prevent callbacks. You can include them in the price or not or not but either way, it will save you more than it costs to do it.
Do these things along with all of the standards tests you perform to make sure that you have no issues and that whatever caused the fault in the system has been rectified and you will save a lot of problems. When the customer spends a lot of money getting a system fixed, they don’t want to turn around and have it fail for an “unrelated” reason.
While this list is clearly tailored to the residential and light commercial air conditioning market, every piece of equipment has its common maintenance items. So what do you do every time when you make a major repair?
When you walk up to a piece of equipment you want to follow a process to ensure that you accomplish five things.
#1 – You diagnose the fault correctly
#2 – If possible you find the “why” of the failure
#3 – Find any other problems or potential problems with the system that can cause inefficiency, low capacity, failure, safety or indoor air quality issues
#4 – Communicate clearly with the customer and and office about these issues via paperwork and / or verbal communication
#5 – Execute and repair the issues in an efficient and workmanlike manner
In order to accomplish this I recommend looking at the equipment with a wide, narrow, wide mindset
First, speak with the customer, read the call history, understand any concerns the customer may have and any past failures. Look at the equipment, look for any obvious signs of issues like oil stains, corrosion, rubbing wires, bloated capacitors etc…
Then go narrow and FIND THE CURRENT PROBLEM. The difference between a “Sales Tech” and a real service tech is the ability to quickly and accurately diagnose the problem at hand as well as find the likely causes of the failure.
Finally, once you find THE problem, go wide again and look for any other problems BEFORE communicating with the customer. Look at coils, contactors, capacitors, filters, belts, wire connections and potential rub outs, check coils and acummulator for oil stains etc…
When looking wide take the mindest that..
– The system was likely installed poorly / incorrectly to begin with
– Every other repair made to the unit was done improperly
This will put you in the mindset to double check everything.
Now you are ready to talk to the customer and make repairs with confidence.
When we say that there is “flash gas” at a particular point in the system it can either be a bad thing or a good thing depending on where it is occurring.
Flash gas is just another term for boiling.
It is perfectly normal (and required) that refrigerant “flashes” or begins boiling directly after the metering device and as it moves through the evaporator coil. In order for us to transfer heat from the air into the refrigerant in large quantities we leverage the “latent heat transfer of vaporization”. In other words we transfer heat into the boiling refrigerant, or “flash gas”.
In a boiling pot of water we create flash gas by increasing the temperature of the water until it hits the boiling temperature at atmospheric pressure.
Inside of a refrigeration circuit we get flash gas when the pressure on the liquid refrigerant drops below the temperature / pressure saturation point or if the temperature of the refrigerant increases above the same point.
This “flashing” can occur in the liquid line when the liquid line is long or too small and also in cases with line kinks and clogged filter/driers. All of these instances result in a pressure drop and a drop in the saturation temperature.
It can also occur in the liquid line if it is run uninsulated through a space that is hotter than the liquid saturation temperature like on a hot roof or in an unconditioned attic. This is more rare and will generally only cause flashing in conjunction with another issue.
This flashing can be prevented by keeping line lengths and tight bends to a minimum, insulating the liquid line where it runs through very hot spaces and keeping the refrigerant dry and clean with one properly sized filter/drier.
It can also be prevented in most cases by maintaining the proper levels of subcooling. A typical system that has 10°+ of subcooling will not experience flashing in the liquid line under normal conditions.
When you walk up to a liquid line near the evaporator and you hear that hissing/surging noise or when you look in a sight glass and see bubbles you are seeing refrigerant that is at saturation, meaning it is a mix of vapor and liquid. This doesn’t necessarily mean it is “flash gas”, it could very well be that the refrigerant was never fully condensed to liquid in the condenser in the first place. This can be due to low refrigerant charge and in these cases the subcool will be at 0° Even when taken at the condenser.
True liquid line “flash gas” issues are cases where you have measurable subcooling at the condenser coil outlet but still see, hear or measure boiling/flashing refrigerant in the liquid line before the metering device.
This article is written by regular contributor, experienced rack refrigeration tech and RSES CM Jeremy Smith. Thanks Jeremy.
A technique that you can use to diagnose compressor problems and to help differentiate them from other possible issues is the use of compressor performance analysis.
Manufacturers do extensive testing of their compressors before they sell them, and a part of that testing is available to you as a troubleshooting tool. The compressor performance chart. I’ll primarily refer to Copeland compressors as they are what I service most, but I’ve been able to find charts and data from other manufacturers through their websites and tech support lines.
Let’s look at a real-world example. I went to do a follow-up check after a major leak and recharge on a set of freezers. On arrival, the cases, which had been running now for 14 or 15 hours since having been repaired, weren’t as cold as expected. Checking the unit, here is what I found:
209v (average of all 3 legs)
Unit at 18-20°F
The suction line was cool to the touch and the sight glass had a thin ‘river’ of refrigerant in it. The high suction pressure really jumped out at me here as worthy of more consideration.
Now, a high suction pressure in this instance can be caused by high load (note the high unit temperature) or it can be caused by a compressor problem. Looking over the data here, I was concerned about the health of the compressor and its ability to pump properly. I did a quick “pump down test” and found it inconclusive. The compressor pulled to 24” Hg easily and held there. Still, I wasn’t happy with this, so I pulled out my smartphone and opened the Copeland Mobile app.
A quick note on pump down ‘tests’. They really aren’t effective on most modern compressors. I performed the test and included the results here to illustrate exactly that fact.
Entering the model of the compressor leads you to select the application (R502 low temp which is closest to R404a low temp). Selecting the “Diagnostics” tab brings you to a screen where you and input pertinent data and the app then outputs both the expected amperage at your conditions and the percent deviation
from the norm.
In this case, my expected amperage was significantly higher than my observed amperage, so the high suction was definitely caused by a compressor problem.
I recovered the refrigerant from the machine and removed the compressor head and valve plate for internal evaluation.
Finding a single broken suction reed, the rest of the internals were intact making this a good candidate for a new valve plate. I Installed new valve plates, evacuated and restarted the machine and re-evaluated operation.
Had this been a hermetically sealed compressor, I would have had no choice but to condemn and replace the compressor. This time, the amperage was within 5% of specifications (sorry, didn’t get a screenshot) and I continued to monitor unit operation until equipment reached 0° F, verified and completed proper
charging of the unit and called it a day.
Why not use RLA (Run Load Amps) (? Or use LRA÷6 (Or is it 8?) to diagnose?
The simple answer is that they just aren’t sufficiently accurate enough for me dealing with high stakes, high dollar equipment and they shouldn’t be accurate enough for you, either.
Let’s return to my real-world example…
The compressor has a listed RLA of 25.8 and a LRA (Locked Rotor Amps) of 161.0. Now look back at the original screenshot of the app. It calls for an amp draw of 17.09A at that set of conditions. If we compared that to the RLA, even the correct amperage looks low. If we use common LRA divisors 161 ÷ 6 gives us 26.83A and 161 ÷ 8 gives us 20.125A. Maybe a little better than the RLA method but still off by a significant amount. Enough to cause concern and possibly lead to an incorrect diagnosis.
Not a one of these methods gives us an accurate expected amperage for this machine. That inaccuracy can lead us to draw a bad conclusion and potentially wasting time and money pursuing a “bad” compressor that is in fact, working exactly as it should.
Like most things in HVAC/R using a fixed operational target without considering the specific conditions can lead to misdiagnosis and a lot of wasted time. You would be surprised what is available within manufacturer specs if you take the time look.
— Jeremy Smith, CM
Proving flame is an important part of the gas firing sequence. Without proof of flame you risk dumping unspent gas into the heat exchanger resulting in an explosion.
There are many ways to “prove flame” we are focusing on the flame sensing rod method here.
Here are the facts-
Flame sensing rods, also know as flame rectifier rods or flame rectification rods are commonplace in modern hot surface and ISI (intermittent spark ignition) gas fired appliances.
Flame sensing rods stick out into the flame and connect back to the furnace board. Once the board sends a call to the gas valve to open, it monitors current flow on the flame sensing rod. It does this by generating a potential (voltage) at the flame sensing terminal, this terminal is connected to the sensor with a conductor. When no flame is present there will be potential at the rod and no current, when a flame is present a small microamp DC current will be present as a path is made between the rod and the ions in the flame. This small DC current signals the board that flame exists and all is well with the world. If it does not sense this microamp DC current within a few seconds it will shut off the gas valve and try again.
The board outputs this potential (voltage) on the flame sensing terminal right at the beginning of the sequence to confirm that the path is “open” with no flame. This ensures against false positives (sensing flame / current when there should be none) andonce it goes from 0 current to the rated micoamp current the board “knows” that flame is present.
These flame sensing rods are “dumb” devices. They do not generate potential (volts) or current (amps), their predecessor the thermocouple (seen in standing pilot systems) does generate a potential itself which is often the source of the confusion.
A flame sensing rod is a piece of metal with a ceramic insulator that keeps it from grounding out. That is all. However because it is conducting in the Millionths of an amp (microamp) a lot can go wrong with it that a normal electrical component wouldn’t have any issue with. Tolerances are tight so small factors make a big difference.
Flame sensors fail when:
Before I go any further I want to address a common question. Do flame sensors have a special coating that can be rubbed off with improper cleaning?
Well… If we are talking about a thermocouple or a thermopile then yes.. absolutely, but we aren’t discussing standing pilot systems here.
I have seen a lot of flame sensing rods, and I have done a good deal of research and I have found no evidence that most flame sensing rods have a special coating on them that can be rubbed off. Now, if you have real, quantifiable proof from an manufacturer that says otherwise.. PLEASE provide it to me so I can retract this statement.
Here are the steps to test a flame sensor –
If you do not have a proper microamp reading you can confirm the following
Once you have established all of the above and you are still not getting the required microamps then you are left replacing the board.
Word of warning –
Test your tools regularly. If you are trusting your meter and you aren’t 100% sure your meter is working and set up properly you may end up with a misdiagnosis. Test and calibrate your tools regularly.
Do every possible test before replacing a board. Many techs advocate just replacing a flame senor if they suspect it isn’t conducting well. I am cool with that so long as
Or.. you just install a new one long enough to test. That is all fine and good if you have extra flame rods in your truck. Many techs do not have that luxury.
If flame rods are getting dirty / coated often, you will want to find out why. There is something in the environment or the combustion that is causing it.
In Summary flame rods should be
Now is the part where the furnace techs from all over the world tear me apart.
Callbacks are horrible… They kill the trade from every possible angle in ways that are hard to fully quantify or make up for. They destroy customer satisfaction, reduce technician morale by causing long hours resulting in unprofitability for companies and less earning opportunity for everyone. Possibly worse of all, callbacks tell customers that you are no better than their cousin the maintenance man or the $35 an hour Craigslist tech. If they wanted to call someone back they could have just called them instead of a true pro.
Callbacks make me furious!
They have always made me furious. Back when I was a tech there was NOTHING I hated more than having a callback… Wait… I take that back, I hated being accused of a callback when it wasn’t a callback in my mind even more.
Since those immature days of pitching a fit whenever I got a callback, I have come up with my definition of what is and isn’t a callback.
Callbacks Are –
What we have learned is that the only way to reliably prevent callbacks is to come up with systems and processes that actively PREVENT callbacks rather than assuming that if you are a good tech they won’t occur. Often we would blame the customer, the follow-up tech or faulty parts for callbacks when it was actually within our power to prevent if we were more proactive. Here is what we learned.
Look Around More Carefully
Before you start diagnosis with tools look over the equipment for anything abnormal. Strange sounds, signs of abnormal condensation and oil spots can all be signs of trouble. Look for wire rub-outs, loose connection and arcing. If it looks like work was done recently, double check that the correct parts were used and that they were installed properly. If wires are a mess, electrical connections exposed, refrigerant lines rubbing out or severe corrosion/deterioration on critical metal parts it should be addressed with the customer.
Never just fix the first problem you find and leave. If that’s all you do you won’t have a low callback rate and you will miss opportunities to serve the customer better. In my experience, the vast majority of systems have either initial installation/commissioning deficiencies maintenance issues, abrasion concerns or just plan faults that get missed when the tech fixes only the first and most obvious problem.
Diagnose More Precisely
The proper and full diagnosis of HVAC/R equipment isn’t that difficult if you are using the proper tools and techniques, but we still hear techs say “it should be fine” when looking at a charge or “That looks pretty normal” when taking an amperage reading. These aren’t things that a good diagnostician guesses at, it is either within design specifications or it is in need of repair, alteration or upgrades and the customer needs to be communicated about it. KNOW the target evaporator DTD, condenser CTOA, motor RLA and system design capacity vs. delivered capacity for the piece of equipment you are working on. If you don’t know what these things mean then start HERE and download the MeasureQuick app to help. Once you stop guessing you will get it right the first time more often and prevent some nasty callbacks.
Improve Your Workmanship
Most bad workmanship is due to poor training, tools, supplies and real or perceived time constraints. You always have time to the work correctly or you need to FIND time to do it again. None of us get everything right, but you can work to improve your workmanship with every job you do whether it is how you make a wire connection to how to connect ducts or making a flare that never leaks. Get it right the first time and leave it looking like a pro did it instead of a handyman or a kid fresh out of trade school.
Keep the right tools and materials on your truck to execute great workmanship and then do it a little better each time based on what you learn along the way.
If parts are required make sure to get photos of EVERYTHING you can find, data tags, parts tags, boards, compressor model and serial etc… going back to a call just to get a model # because it was missed or written down wrong is a huge waste of time.
Eliminate the Careless Errors
Walk the job before you leave and put your tools away in their proper place. This will help prevent leaving disconnects out, caps off, float switches tripped, thermometers in the duct, screwdriver on the roof etc…
Some of you are just more prone to these sorts of careless mistakes but that is not an excuse, you just need to come up with systems that prevent these forgetful errors. Here are the best ways –
The final test is a gut check. If your gut tells you the diagnosis isn’t right, you didn’t make the repair right or the customer isn’t 100% understanding what’s going on then please DON’T LEAVE.
I know it can be tempting especially after a long day or an especially difficult call or customer but trust me, leaving never makes it better. Hang in there, read up on the system, perform more tests, check the ducts again whatever you need to do but don’t bail.
Sometimes you will have a customer that you just know is going to turn around and call back. You can tell they aren’t listening to you about your findings or they have a misunderstanding about the system operation. These are the ones you want to MAKE SURE you get your recommendations in writing, clearly spelled out with a signature.
If you really want to ensure it doesn’t come back, spend 15 extra minutes and write them a nice, positive email and copy your dispatcher and your service manager with a description of what you found, what you recommended, what you repaired, any system condition issues and how they should expect the system to operate with photos attached. It will really reduce those immediate callbacks from difficult customers.
Which do you connect to the plug and which to the drill.
Come up with what you think…. we will wait…
If you said connect the nice one first (to the plug) you would agree with 95% of people.
The answer is. It MAKES NO DIFFERENCE.
An extension cord creates a full circuit.
From hot 120v down both cords to the load (the drill) and back through both neutrals to the neutral plug terminal.
The resistance (opposition to current) and ampacity (safe current carrying capacity) of the circuit is for the entire circuit, period.
We can often fall into the trap of thinking of electricity in terms of points in the circuit. There are good reasons for that in diagnosis, but the end result is the entire circuit between two points of differing electrical charges (potential difference) and the amps, amapacity, voltage drop, watts and resistance of the entire circuit are really what matter.
An electrical circuit is only as good as its weakest link. Unlike sausage…. because all sausage links are delicious.