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Basic Refrigeration Startup & Commissioning
Let's take a walk through the startup and commissioning procedure of a conventional or “single” refrigeration condensing unit. We’re going to start with a unit that is fully piped in and has been pressurized for leak and strength testing. For brevity, we are going to assume a basic familiarity with industry standards, company and customer policies, requirements, and the job site and any policies in place there. Before we even swing a wrench at the machine, let’s familiarize ourselves with the job site and equipment.
Take a walk around, check with the job supervisors, check in with other trades, etc. Find all the equipment you will be starting and make notes.
Step one is to make final leak tests. Typically, the installer records time, date, and pressure data. If you put the pressure charge on the equipment, you should have done so. If you have had any temperature change, you MUST account for that. While nitrogen is chemically inert, all gases respond to changes in temperature by changing pressure. The math is simple, and I've addressed it in another article.
We'll assume here the installers did their job properly and that there are no leaks to track down and fix. Blow that charge off and break out a nitrogen cylinder. Yeah, I know; you just blew off the nitrogen. That's OK—you aren't leak-checking anymore.
Disconnect the pressure controls; you're going to SET them. If they're the little-encapsulated type, we're at least going to check and record the operating pressures. If they're of the brazed in variety, you’ll need to try to isolate parts of the system to pressurize them to test. I recommend referring to the manufacturer's literature for proper control settings and, if they don't offer a guideline, referring to the Heatcraft installation manual for guidance.
Use your nitrogen regulator and manifold gauges to adjust each control precisely to the setting desired. The procedure that I typically use is to adjust the control to a setting near the top of the scale, set the applied pressure with the nitrogen to the desired pressure, then adjust the control down until it closes. Some controls have a very audible ‘click’ when they open and close, and others will require you to use an ohmmeter to determine when the contacts open or close.
Use a Sharpie to record that setting right on the cover of the control or, if you prefer, inside the electrical control panel. Since many larger customers have specific commissioning paperwork they require, you might as well get your notebook out and record it there, too.
Once you're done setting the controls, it's time to evacuate the equipment. Make sure you've opened any and all service valves in the system and that any control valves are open or that you're connected on both sides of the valve.
Even though you've got a lot of work to do while the pump is running, I still prefer to use the faster no manifold, large hoses, core-pulling method. That way, I'm spending more time in a deep vacuum. Also, if something goes wrong and I have to make a repair and evacuate the system a second time, I'm not spending a lot of time watching a vacuum pump run. I'm not even digging my micron gauge out just yet; just hook up the pump and let it run.
While the pump is running, you've got some details to attend to:
- Record model and serial of the condensing unit and the indoor equipment.
- Check phase rotation if possible. If not, you will check this during the initial startup. Remember not to energize equipment while under a deep vacuum.
- Check and tighten all electrical connections. I prefer to use a torque indicating device for this just to eliminate any chances I can for a problem down the road.
- If there are flanged or threaded connections on the refrigeration system, I'll check and torque or tighten them at this time as well. Again, I prefer to use a torque indicating device when and where possible.
- Check that the metering device, condensing unit, and oil type match the refrigerant being used. Make sure TEV bulbs are installed properly.
- If the unit has a headmaster and a fin/tube condenser, strip the panels off of the unit and measure the condenser for calculating a flooding charge. Go ahead and figure it and write that down, too. Microchannel coils just have a lookup chart.
- Verify that any other trades involved have completed their work. It's no fun to have a piece of equipment ready to run and not have power to it or to find out a day later that a condensate drain wasn't properly installed or heated if necessary.
- Check any doors on fixtures to make sure they close and seal properly. Make any adjustments needed.
Get that micron gauge out now, and let's check the progress of our evacuation. Again, this subject has been extensively covered, so I don't want to belabor the point of the how and the why here. Pull a proper deep vacuum on the equipment according to the customer's standards, the manufacturer’s standards, or industry standards and record times and evacuation levels here if the commissioning paperwork requires it.
Evacuation complete, here is where starting a refrigeration unit diverges from starting up a residential one. Residential equipment typically comes precharged for a specific amount of line set length. All you have to do is open the lines, start the equipment and check the charge. Split refrigeration equipment doesn’t come precharged because the manufacturer can't know how their machine will be installed. We will have to field charge it.
Final checks before charging:
- Power to the unit on? Leave the disconnect open for now.
- Power to the evaporator unit? Go ahead and turn that on.
- Power to any control valves like a liquid line solenoid?
Put the cylinder on a scale and start adding refrigerant to the equipment. Techniques vary somewhat here, but I start by adding liquid refrigerant straight into the receiver valve and liquid line while monitoring suction pressure. Suction pressure is rising, so we've got flow through the system. If we don't see a suction rise, we need to stop and investigate. Maybe a valve is closed or not energized properly. For us, everything is going nicely, so we can go ahead and close that disconnect to the condensing unit to energize the equipment. If you weren't able to test phase rotation earlier, now is the time. Verify that the compressor and fan motors are rotating in the correct direction, and make any corrections necessary before proceeding any further.
While adding gas, the compressor will short cycle a fair bit while you're getting enough refrigerant into the system to keep it running. Some guys like to bypass the low-pressure safety, and I’ve done that. I'm also not opposed to opening up some liquid to the suction line. Not full flow, but get some in there.
For right now, we're going to charge this unit to a moderately cloudy/bubbly sight glass. We'll come back and finalize the charge later, and I've always found it easier to start low and add up to the final charge than to add too much and have to remove some or be uncertain of our charge. It'll work, sorta, even low on charge. Once the machine is running on its own, add just enough to get that sight glass in that cloudy state and stop. Record the amount of refrigerant added in your notebook. Monitor pressures and suction temperature for right now. If your superheat really starts to drop into the flooding range, it's time to go check the evaporator to see why, but that's pretty rare.
Continually monitor the temperature in the box while monitoring the unit operation until box temp gets to within 5° or so of the desired temperature.
Now, we get to do some wrench twisting.
First things first, you MUST HAVE a solid column of liquid to continue, so add the rest of the charge. Clear the glass and add your flooding charge. Then, record the total amount of refrigerant added both on the unit and in our notebook.
Now, let's go check and set the superheat. Having a box that is close to temp and a solid column of liquid is important because without both conditions being present, a TEV cannot properly regulate superheat at the coil. Connect your gauges and temperature probes and monitor for a couple of minutes. Again, record the information: pressures, temperatures, superheat—write them all down. Adjust the superheat to the manufacturer's or customer's specifications. As you're doing this, be aware that the unit may cycle off and throw your readings off. You can adjust thermostats or bypass controllers to keep the unit running while doing this, but be careful not to allow the unit to get too cold, as this will affect the operation of the valve under normal conditions.
Let's look at the final details and check out.
Now that our unit is running and we've got everything set up right where we need it, we need to turn our attention to details.
- Set the thermostat or temperature control and verify the setting with an accurate thermometer.
- Set the defrost timer to the manufacturer's specifications or the customer's specifications. Test operation of the timer as well and ensure that it not only keeps time but switches properly. Then set the timer to the correct time of day. If requested, provide the customer with the defrost schedule. Verify that any defrost heaters draw proper amperage and record.
- Many cases and freezers have mullion heaters to prevent frost and condensation on doors and frames. Check these for proper amperage and record.
Now we can sit down, fill out the customer's paperwork and submit that to them.
Before leaving the job site, it should go without saying that we need to clean up any debris left behind. I also like to present the customer with their case manuals, give them a quick run-through of the equipment, and answer any questions. Be sure to leave a business card because even though we've been diligent in starting and commissioning this equipment, they may have problems or just questions down the road.
—Jeremy Smith CM