Oh no! Your walk-in is warm again, isn’t it? Man! Sometimes you just can’t catch a break. In Texas’ unrelenting summer heat a warm walk-in is never good news. Well we’re going to go over ten eleven things to check on your walk-in that could be the problem. Hint, 80% of the time it is not low on refrigerant. The information below is for educational purposes. If you attempt any diagnosis on your own based upon what is written here, you are responsible for your actions but you know that already, don’t you? This began as a short list of possible problems with short descriptions and morphed into thousands of words about what could be wrong with your cooler and what steps we take to solve the problem. Considering this, I broke this post up into multiple blog posts rather than overwhelm readers a five thousand word blog post. They are useful words but too many might be less than helpful. We want to be helpful.
10 common reasons why your walk-in isn’t working. Part 5
10. TXV (AKA Thermal Expansion Valve):
The TXV controls the flow and pressure of refrigerant in the system. This part in the evaporator of your walk-in cooler or freezer and drops the pressure of the refrigerant from the high pressure side coming from the condenser to the low side going to your evaporator. Since pressure and temperature are tied together, as the pressure is dropped so does the temperature. If it is not regulating the pressure correctly or at all your system will not work correctly. The TXV does not operate constantly at the same exact pressure and this is by design. It modulates the pressure within certain boundaries. This modulation is based on the temperature of the bulb. What could be wrong with the TXV? A few things are normally the culprit and here is what we initially check to find out if the TXV is functioning. Before we point the blame to the TXV there are quite a few things to establish first. Is there refrigerant getting to the TXV? Is the pressure high enough when it gets there? Is the compressor keeping up the pressure. Is the condenser fan motor running when it shouldn’t causing low pressure to the TXV? Has the superheat been set on the TXV? There are so many possibilities but what we check when we think it is a TXV issue is:
This may seem elementary but the first thing we take a look at is if the TXV bulb is installed correctly. The bulb is supposed to sit on top of the suction line at about 2 o’clock and be secured against the suction line with pipe clamps on a horizontal section of pipe. It should be insulated. The bulb is what determines how open or closed the TXV is going to be. If it is in the wrong place or not installed at all it will not work correctly causing issues. You might ask, how has it worked this long like this? What has suddenly changed? I typically liken a walk-in refrigeration system to a human body. When you were young you could go on a ten mile hike without warming up or cooling down and do it again tomorrow without anything hurting and no ill effects. When you are older, your body doesn’t bounce back like it used to. The day after an impromptu 10 mile hike when you are no longer a young person you are hardly able to get out of bed. Yep, it’s the same way with machines. Just because it worked while being abused when it was brand new doesn’t mean that after a few years that it is going to keep functioning with the abuse.
If the bulb is placed correctly we check to see if the bulb is modulating the pressure int the TXV. This can be done by pulling the bulb off of the suction line and holding it in your hand and watching the suction pressure taken at the evaporator. It might take a minute or two to react if it is still functioning correctly. With the TXV held in your hand it should open the TXV valve all the way and raise the pressure in the evaporator. If you don’t see a change after a few minutes in your hand there is almost certainly a feeding issue with the TXV.
Something that is often overlooked is the TXV screen. The screen is on the inlet of the TXV and prevents dirt and crud in the refrigerant system from getting to the TXV and clogging it up. The down side of the screen is that the screen clogs up instead of the TXV and causes the same problem. To access the TXV screen we first have to pump down the system to reduce the pressure in the lines otherwise refrigerant would be vented and no one wants to do that. To access the screen on Q-body TXV after the system has been pumped down we unbolt the screen nut from the TXV. If the screen looks dirty we will clean it with a solvent and bolt it back into the system. If it’s clean it is more than likely time to replace the valve as something internal has failed.
I always loved the name of this part as it is a clever play on words though it isn’t really accurate about what it does. It does click and turn on but the name is a little deceptive because it does more than that. It is a part that lives in the walk-in freezer evaporator and is activated by temperature. What does it control? The evaporator fans and defrost termination. Evaporator fans: When a freezer is in defrost the time clock shuts off its fans. The reason behind this is to prevent ice melting off the evaporator from being blown around the room as drops of water. Drops of water become ice again on the floor and create a treacherous landscape for people walking into the walk-in. No fan equals no ice on the floor to slip on. The Klixon’s job is to delay energizing the evaporator fans until it refreezes the coils. Defrost termination: While this sounds like the title of an 80s Schwarzenegger movie it is not. The time clock that controls defrost has two ways of ending the defrost cycle in a freezer. It can run out the clock on the rotating clock and terminate defrost after a set amount of time or it can use the Klixon to end defrost by temperature. Once a Klixon gets to a set temperature above freezing it sends a signal to the time clock to end the defrost cycle. This is done because there is no reason to continue thawing out the evaporator coil if all of the ice has been melted away. It would be a waste of energy. How do we diagnose this part?
If the fans aren’t running and refrigerant is flowing we will check for power at the fans to eliminate the fans then we will move on to see if there is voltage at the time clock. If it passes those tests we will bypass the Klixon and see if the fans will operate. Sometimes the internal switch gets stuck or occasionally the temperature sensor gets out of whack and will not turn the fans back on.
Sometimes the klixon will not send the signal to the time clock to terminate defrost. By observing the time clock it can be determined that defrost will always run the full length it was set for instead of being terminated by the Klixon. Another thing to double check when diagnosing this type of issue is if all of the ice is melted off of the coil. The heaters in the evaporator might not all be working and it is possible that the Klixon is working but never gets warm enough because the heaters aren’t all working.
You made it! You made it through all ten, uh, eleven of the most common problems with walk-in coolers and freezers. You have enough information to officially be dangerous. If you are having trouble with your refrigeration equipment in Austin, TX or in Lubbock Texas give us a call for service or new equipment. We are always happy to help! 512-651-4565 in Austin and 806-686-0050 in Lubbock, Texas Or Visit our website at www.tripointrefrigeration.com
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