VENOM PACK CONDENSER You would then setup a length of time for the defrost as a best guess with too long wasting energy and warming the product or too short resulting in incomplete defrost and gradually freezing the coil. For this test to work properly, we need a coil that is free of large ice buildup but that has a ‘normal’ frost on it. The basic timer type defrost initiation control doesn’t change. When the temperature reaches 50-70 degrees (F) the defrost bimetal turnd the defrost heater off. " We also don’t want to blow hot, humid air around the refrigerated space. Remember that copper can expand over an inch per 100’ of pipe with a 100°F(55°K) change in temperature, so we have to consider the expansion and movement of the piping. Why? Regardless of the location in the system, the valve is typically adjusted for an 18-20 PSI (1.24 bar – 1.47 bar) differential setting. We all learned about sensible and latent heat in school, right? After I jumpered the thermostat out, it came on and got up to 482 defrees F (according to the temp probe on my cheap digital multi meter). Let’s start with the basics and move on from there. Much of the timing depends on the length of the suction line and the amount of frost buildup on the coil. The defrost ends when the copper-colored pointer on the inner ring rotates past the same pointer. Because this is a cooler (and not a freezer) it is set to defrost by simply shutting off the compressor four times per day while still running the evaporator fans. 3. Most T-stats have numbers on them telling you their range. This relies on appropriate over-sizing and can lead to issues when the heat or moisture load is high, especially when the door are opened a lot for loading and unloading. This digital timer has little black bars on the display indicating both time and duration of defrost. A discharge differential won’t work for Kool gas. Well, melting frost is just latent heat added to change the state, right? With this time only strategy you are left guessing and in order to prevent progressive freeze ups you will always need to defrost a little too long. The biggest difference is that now, with a timer, instead of being subject to the unknown of when the system will cycle off and how long it will take to melt the frost, assuming the time of day is set correctly, you can reliably predict the defrost times. This topic is now archived and is closed to further replies. There are no interconnecting wires between the evaporator and condenser, which is common on remote walk-in systems. At the same time the differential valve activates, both of these valves activate and start the defrost process. But there has to be a better way, doesn’t there? Dryer T-stats have something like 155 -40. Don’t Forget to Report Any Irregularities or Alarms. The temp range is listed on the defrost thermostat/switch. A similar method for defrost control uses a pressure control to cycle the compressor. We use time to make a solid at how long it will take to reliably defrost the evaporator coil and then we use temperature to terminate (stop) the defrost once the coil warms up enough that we are sure it is no longer ice bound. FAQs | Repair Videos | Academy | Newsletter | Contact, By At what temp should a defrost heater thermostat typically close? All is well. 13% off. It is common to setup freezers for 2 (dry) to 6 (Humid) defrosts per 24hr period depending on the climate and how they are being used. Photo caption:  the grey bodied valve, installed in the vertical line stops refrigerant flow to the compressors. Most Thermo Kings and Carrier units defrost on their own at certain coil temperatures. Let’s “follow the gas” and try to visualize what’s happening during this defrost. Even when things go right, mechanical failures are always a risk. They aren’t running. This is more common on hot gas defrost system as opposed to Kool gas systems. The most common are referred to as a DTFD control (Defrost Termination Fan Delay) or 3 wire control. Most techs who are familiar with heat pumps understand the basics of a gas defrost but when we apply this strategy to a larger system where we’re only reversing a small part of the system while we need to add some controls and valves to get the job done optimally. Because this is a cooler (and not a freezer) it is set to defrost by simply shutting off the compressor four times per day while still running the evaporator fans. Why? Before we cover these terms lets set the basic defrost groundwork for refrigeration (coolers and freezers), Defrost is accomplished in one of a few ways, these first two only apply to “coolers” where the box, air and product temperatures are above freezing but the coil temperature drops below freezing –. It will spell out frequency or interval (time between defrosts) and duration of the defrosts. With either a little-coiled bulb on the end of the sensing tube or a tube that kind of embeds in the evaporator, this senses the temperature of the evaporator coil and cycles the compressor based on that. In this case, because this particular sensor closes in colder than 32-degree temps you can’t even use a (freshwater) ice bath to test it. Even when things go right, mechanical failures are always a risk. Once either the time limit is reached, or the termination temperature is reached, all of those valves return to their normal positions, and the refrigeration cycle resumes normally. When the condensing unit controls are strictly two-wire low voltage there is no continuous low voltage power so there are also no timers or other logic in the condensing unit. Derived from refrigeration grade lubricants. Wait a minute or two and the coil will freeze that last bit of moisture. If the differential valve fails, we won’t have an adequate flow of refrigerant to get enough heat for a complete defrost. Get the (near) daily Tech Tip email right in your inbox! Defrost Thermostat Series Ksd301b 37t&14t , Find Complete Details about Defrost Thermostat Series Ksd301b 37t&14t,Defrost Thermostat,Ksd301,Thermostat from Other Home Appliance Parts Supplier or Manufacturer-Long Term Inc. The number 3 and number 8 thermostats are especially important for refrigeration system builders. The one shown above is a Carrier Defrost Thermostat and it closes at 30 degrees +/- 3 degrees and it opens at 65 degrees +/- 5 degrees. Is 482 degrees about right for these heaters? Range & Oven Parts; Refrigerator Parts; Washer Parts; All Appliance Parts; Find Your Parts - Help me find my model number. 4. i quit drinking the day i woke up nude on the hood of my car with my keys up my butt, first thing i do with the frigidaires that dont defrost is visually inspect the DTS cause most of the defective ones i see the plastic top is actually popping off them, fellow,academy of sublime masters of appliantology. Usually the range is more like 50 -20. The line leaving the distributor allows condensed liquid to leave the coil, bypass the metering device and re-enter the liquid line through a check valve. So, when an A/C coil starts to get cold and that little bit of frost starts to build on the tube surface and the fin, it affects airflow through the coil much faster than it would if the fins were spaced more widely apart. Electric Heat Defrost – On a set schedule (time) the compressor is pumped down or cycled, the evaporator fan is (generally) shut off and the electric heaters are turned on inside the evaporator coil. If your fail safe time is 30 minutes this means that once a defrost cycle begins the LONGEST it will remain in defrost in 30 minutes regardless of the defrost termination thermostat. Almost all electric defrost systems will have a type of defrost termination built in. Out in the evaporator, we’ve got a check valve piped to bypass the TEV. You CANNOT jump out a thermistor with a typical jumper to test. If your load can tolerate 5-10 degree fluctuations from your set temperature, then your auto start-stop mode is the best way to go. The same type of timer is used and when defrost initiates, the refrigeration circuit de-energizes the same as before. It depends on the design of the refrig. First, we need to create a pressure differential between the gas we’re sending into the evaporator and the liquid line. If we had refrigeration coils with fin spacing like an A/C unit, it would ice up too quickly, and we couldn’t get anything done. There are many different valves that are applied to do this and an in depth treatment of each valve isn’t really possible here, so we’ll just look at the 2 most common places they’re applied. The unit will either keep the refrigerator running too long, causing cold food to freeze or it won't run the refrigerator often enough to keep the interior temperature below 40 degrees.


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