Month: July 2018
This article is part 5 of a 5 part series on troubleshooting by Senior Refrigeration and HVAC tech Jeremy Smith
This might be the most challenging part of troubleshooting. We’ve got a “Most Likely candidate” for the trouble, but we don’t know for certain that’s what is wrong.
So, we have to combine our customer skills, our experience, and our troubleshooting skills.
Let’s correct that “Most likely” problem that we’ve identified. Clean a dirty evaporator or
condenser coil, replace the plugged filter drier, repair the leak and recharge the unit to
specifications…
You’re done, right?
Not so fast…
This is where things can get interesting. Looking at our flowchart, we’ve got a decision loop
here. Make the repair or correction to system operation, then reevaluate system performance. In
reality, this puts us back to the gathering data phase of the process, but we don’t have to
Necessarily gather the same data twice. If we replaced an air filter or a belt or we cleaned a
coil or replaced a capacitor, we can ignore that on our second (and maybe
subsequent) evaluations.
We’re now looking at system performance. Most manufacturers publish methods to evaluate
their systems. If those fail, we can always resort back to the ‘rules of thumb’ and check to see if
our system operations data now falls into line with accepted industry norms.
If the unit doesn’t match up with manufacturers specifications or industry standards after making
the initial repair, continue the data gathering, data evaluation and repairing the next most likely
problem the data points to.
Be very careful here not to focus on a single aspect of the system. Let’s say you had a high-pressure
trip due to a dirty condenser. So, you clean that coil and reset the pressure switch.
Don’t key in exclusively on the high side readings and miss a low superheat issue. Monitor
ALL of the system conditions and only when everything is within industry norms (or the
customer refuses the work, of course) do you move to the final part of the flowchart and
terminate the troubleshooting process.
Now go out and fix some stuff right the first time.
— Jeremy
We show the unique way this bristol compressor is wired that allows it to run in different directions to vary the capacity (unload).
–Bryan
We cut open a burned out scroll compressor and show what’s inside.
–Bryan
In this video, we test a high-quality Fluke Megohmmeter against two cheap Chinese versions from Amazon and see how they perform.
–Bryan
We cut up a Bristol recip that is shorted to ground and we see what we can find out.
–Bryan
We show how to loosely determine a refrigerant type in a tank using the PT chart built into the Testo digital manifolds.
–Bryan
This article is part 4 of a 5 part series on troubleshooting by Senior Refrigeration and HVAC tech Jeremy Smith
Ok, so we’ve got our data scribbled and scratched out on paper. Maybe a bit of grease, dirt and oil, too, if you’re doing things right and blood if you’re doing it wrong.
Now, time to take a short break and congratulate ourselves on doing it right while sitting and thinking. Have a coffee and look over your data. Now you have some decisions to make.
Much has already been published on analyzing data on a refrigeration system, so I don’t think I need to reinvent the wheel here and review various combinations of pressures, superheat and subcooling and airflows. If you haven’t yet internalized this information, don’t be afraid to have a nice laminated copy of the printout on your truck until you do.
The thing to remember here is that the more data you have and the more accurate that data is, the easier troubleshooting will be for you.
As an example, if you’ve got a unit with a TEV running a 10° subcooling and your low side shows a lower than expected suction pressure and superheat, do you have an airflow problem, a low load problem or a sizing issue? Without collecting good data, it can be difficult to distinguish between the problems but, if you’ve taken TESP readings, return and supply dry and wet bulb temps and have the unit model/serial info on hand when you sit down to analyze the data, the problem should be more apparent.
Evaluate the patterns in the data. Look broadly at all the data and see the patterns. If you have a good data set and a good understanding of the operation of this equipment, a “Most Likely” candidate for the problem is going to emerge.
The final step is coming tomorrow.
— Jeremy
This article is part 3 in a 5 part series by Senior Refrigeration and HVAC Technician Jeremy Smith
Let’s start with Step#1 in the flowchart.
Gather data.
This is why we spend money on those fancy digital manifolds, shiny electrical meters and other gadgets, widgets and doodads. It isn’t to brag about them on Facebook, it’s to find problems better and faster than someone else.
So, before you start trying to change things, start by gathering and recording data. Inspect filters, inspect coils. Look over the wiring. Check your voltages, resistances, airflow, pressure readings, temperature readings. Locate any open switches in the control circuit and try to determine WHY that switch is open. A pocket notebook is nice but, for larger problems, I’ve taken to carrying a full sized college type notebook.
This gives me more room on the page to write my notes, draw pictures, scribble thoughts and observations about the equipment I’m working on.
Write down every measurement and reading. EVERYTHING. Even if you find that capacitor blown up and you “just know” that’s the problem, take your time and keep looking.
Before we leave the Data Gathering step, we do need to take whatever steps are necessary to get the equipment running if it isn’t already and gather another set of data
Once you have all this data together, we can proceed to Step #2. Analysis.
— Jeremy
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