Hey, thanks for watching in this video. I Partner with our technician Corey Cruz and his Channel's bad TXV on Tick Tock and the official bad taxi on Instagram to create this video to talk about Pump Down Refrigeration Systems. Now this is one of the most thorough, time-consuming 3D model videos we've ever done and we walked through a lot of different aspects. So this may be a video that you kind of stop and Rewind and restart and kind of pick specific sections.

Because we talk about the refrigerant cycle, we talk about the necessity for pump down in many refrigeration systems and we talk about the electrical controls. I Know you're going to gain a lot from this, especially if you're an AC technician. Learning more about Refrigeration as both Corey and I are, we started in AC and moved to Refrigeration that's really the target audience for this. Again, big thanks to Corey for helping outline this video and doing the voiceover.

Thank you in this video. We'll be going over the basic working principles of an automatic Pump Down Refrigeration system otherwise just known as a Pump Down System Automatic Pump down is a common control strategy used in refrigeration in which we will automatically pump the refrigerant that is in the low side of the system into the condenser and liquid line receiver. Whatever. There's not a call for refrigeration such as in defrost or when the Box temperature is satisfied.

So why is it a good idea to pump down the low side of the system in the off cycle? Why can we not simply turn the system off without pumping It down when there's no call for refrigeration such as in your typical air conditioning system. The fundamental purpose for the use of automatic pump down in refrigeration is to protect the compressor. This is done by preventing the migration of refrigerant from the low side of the system to the compressor crankcase during the off cycle, as well as eliminate the possibility of vapor refrigerant condensing back down into a liquid. This can cause extreme damage to the compressor upon a call.

For refrigeration, systems that are installed in colder climates are especially vulnerable to refrigerant migration. However, migration could occur in any climate. during longer off-cycle periods or when the system is in defrost, the consequences of refrigerant migration are catastrophic to any compressor. Vapor Refrigerant entering the compressor crank case during the off cycle will mix with the compressor's oil and condense into a liquid.

This will lead to the loss of the oil's lubricating properties and cause mechanical wear, scoring, and overheating of the compressor's components over time. If the refrigerant migration is severe enough, the pressure in the current case will rise to a point where foaming oil can be forced into the compression chamber of the compressor and lead to a flooded start situation. Upon a call for refrigeration, a flooded start of the compressor occurs when refrigerant vapor migrates and condenses inside of the compressor crank case. During the off cycle, When the compressor starts up again, the refrigerant in the crankcase will rapidly boil off and leave the compressor, potentially taking oil with it and forcing that oil into the compression chamber.

Because liquid cannot be compressed, extreme damage can occur to many different components internally and the compressor, leading to premature failure. So for these reasons, if we were to leave refrigerant in the low side of the system during the off cycle instead of utilizing Automatic Pump down, it is not a matter of if compressor damage will occur, but when compressor damage will occur. There are three main control components of an automatic pump down system. It is important to understand these components and how they work together to ensure that the system has a safe and reliable pump down.

During the off cycle, the first component we will talk about is the thermostat. The thermostat is typically mounted at or near the evaporator head unit inside of the box. The thermostat sensor or sensing bulb will be mounted close to but not touching the back of the evaporator coil and this will read return air temperature. The thermostat's relays close on a rise in temperature.

This means when the temperature of the Box rises above the set point of the thermostat, the relay contacts inside of the thermostat will close. This will send power through the contacts and into the liquid line solenoid. Next we have our liquid line solenoid. The liquid line solenoid is installed on the liquid line of the system and can be located at The evaporator or at the condenser.

It is commonly referred to as a pump down Solenoid. This is a normally closed solenoid and will open which will allow refrigerant to flow through during a call for refrigeration and close in the off cycle, stopping the flow of liquid refrigerant into the evaporator which will allow the system to pump down. This is usually wired in series with a thermostat. Finally, we have our low pressure controller.

The low pressure controller will be installed at the condenser and will be wired in series with a contactor coil. These are usually adjustable because depending on the application and refrigerant used your cut in and cut out, pressures will vary, but it will typically be field set at a pressure low enough to allow for a proper pump down, but high enough that it will not risk short cycling the compressor if there is a slight pressure rise during the off cycle. So how does this all work well? We begin with the thermostat. When the temperature in the Box rises above the set point of the thermostat, the thermostat will call for refrigeration.

The contacts on the thermostat will close and send power to the liquid line solenoid. The liquid line solenoid will then energize and the plunger located inside of the body of the liquid line solenoid valve will open up. This will allow refrigerant to flow through the valve and increase the pressure on the low side of the system because of the increase in pressure on the low side of the system from the solenoid valve, opening up, the pressure on the low side of the system will rise past the field set cut in setting of the pressure controller located at the condenser. The pressure controller, which is wired in series with one leg of the contactor coil, will then close.

This will complete the circuit and allow the contactor to pull in and the compressor and condenser fan motors to operate. This process repeats itself and reverse during the off cycle. During the off cycle, the contacts on the thermostat will open, removing power from the liquid line solenoid, causing the solenoid to de-energize the plunger inside the body of the liquid line. Solenoid valve then closes, cutting off the flow of liquid refrigerant into the metering device and evaporator coil.

The system then begins its pump down. The compressor and condenser fan motors stay energized during this process until the suction pressure of the system reaches the field set cut out setting on the pressure controller. Once the system has reached its cut out setting, the contacts inside of the pressure controller will open and de-energize the contactor coil, causing the compressor and condenser fan motors to turn off. There are numerous different ways that you can accomplish a successful Automatic Pump down, but the fundamental principles are all the same in this first video.

We will be keeping things very simple to demonstrate the fundamental principles of how Automatic Pump Down systems work. Always ensure to reference the installation or service manual for the system you're working on for any deviations that you might see from this video. For this demonstration, we are working with a medium temperature R404a walk-in cooler. The walk-in cooler has a box temperature set point of 36 degrees Fahrenheit.

The Box temperature is high enough that utilizing a defrost clock is not necessary in this application. Instead, the evaporator coil will naturally defrost in the off cycle when the Box temperature is satisfied and the system is pumped down. depending on wide range of conditions and manufacturer's specifications that you might see in the field. Some units might utilize a defrost clock, even a medium temperature applications.

So once again, always consult your installation or service manual for the system you're working on for clarification. In later videos, we'll be illustrating various defrost methods, so stay tuned. Our evaporator will be receiving 120 volt single phase incoming line voltage which will power our evaporator fans, liquid line, solenoid, as well as our thermostat. Our walk-in cooler evaporator fans will stay constantly energized while the system has power.

Even in the off cycle, This is typical in most medium temperature applications. The condenser will be receiving 208 volt three-phase power. We will begin at the evaporator coil inside of our walk-in cooler. Our walk-in cooler evaporator is being supplied with 120 volt single phase power leg.

One of our incoming power will be landed on Terminal F in our factory installed terminal block. Inside of the electrical panel of the evaporator, our neutral wire will be landed on Terminal n on the factory installed terminal block. Our evaporator fans are 120 volt fans. They will be wired on the same terminal as our line voltage terminals F and terminal N.

This will supply our evaporator fans with 120 volt single phase power. At all times, they will stay energized and running unless the breaker or disconnect is turned off. Next, the thermostat needs to be wired in series with the Liquid line solenoid. To accomplish this, a wire is ran from the F1 terminal on the terminal strip to one side of the thermostat, providing it with 120 volts of constant power.

A separate wire is ran from the output side of the thermostat directly to one side of the liquid line solenoid valve. Since our Liquid line solenoid valve is 120 volts, we will need to connect a neutral wire to it. We will accomplish this by running a wire from our N or neutral terminal on the factory installed terminal strip directly to the other side of our Liquid line solenoid with the neutral wire connected to one side of the liquid line solenoid and our 120 volts wire connected to the output side of the thermostat. When the thermostat's contacts close, 120 volt power is sent to the Liquid Light solenoid and our circuit will be completed and The liquid line solenoid will energize.

Now that our thermostat, evaporator fans and liquid line solenoid are wired up, it is time to move on to the condenser section. The condenser is being supplied with 208 volt three-phase power. In this demonstration, we simply need to power our pressure controller and contactor coil. Our contactor coil is rated for 208 volts to power one side of our contactor coil.

We'll simply take a jumper wire from the terminal L3 on the line side of the contactor to one side of the contactor coil, which will supply it with 120 volt power. With one side of the contactor coil being supplied with a constant 120 volt power from the L3 terminal on the contactor. We simply need to supply the opposite side of the contactor coil with 120 volt power to energize it. Since we don't want the contactor to stay constantly energized, we will be breaking the opposite leg of 120 volt power to the contactor coil with the pressure switch.

To accomplish this, we will run a wire from the L1 terminal of the contactor directly to one side of the pressure controller. Next, we will run a wire from the output terminal on the pressure controller directly to the opposite side of the contactor coil. This way, the contactor coil will only energize when the pressure controller's contacts are closed. The pressure controller will close when the pressure on the low side of the system reaches the set cut in setting on the controller.

When the pressure controller contacts close, it will supply the opposite side of the contactor coil with the second leg of 120 volt power needed to pull in the contactor coil. This will energize the compressor and condenser fan motors. Finally, we must set the pressure controllers, cut in as well as cut out set points to fit our application and refrigerant. This should always be finalized and confirmed with pressure gauges before leaving the job to ensure your adjustments are accurate.

Since we are using our 404a refrigerant in a medium temperature application utilizing Automatic Pump down, we will be setting the pressure controller to cut out at 5 PSI and cut in at 15 psi. Always consult your manual to confirm the proper pressure control set points for your application. This is where many technicians get confused. On most pressure controllers, You will see two settings which you can adjust those being your differential setting and your cut end setting.

To set your cut in pressure, simply adjust the dial on top of the pressure switch to your desired cut and pressure. In our application, we will set the cut in pressure to 15 psi. To obtain your cut out set point, we must subtract our differential setting from our cut end setting. For example, since we have our cut end setting at 15 psi and we would like to set our cut out set point at 5 PSI, we will need to adjust the differential setting on our controller to 10 psi.

This will give us a cut out setting of 5 PSI. Again, your cutout setting is your cut in setting minus your differential. Our cut end is 15 and our differential is 10.. So our cut out setting is 5 PSI.

So now with the pressure controller set up, we are now ready to turn the system on. With both condenser and evaporator disconnects turned on and proper power applied to the evaporator and condenser, we will initiate a call for refrigeration. Our evaporator fan motors are operational and one side of our thermostat is receiving 120 volts of power. We'll adjust the thermostat dial to 36 degrees Fahrenheit and due to the Box temperature being warmer than 36 degrees Fahrenheit the contacts inside the thermostat will close.

The thermostat then outputs 120 volts to the liquid line solenoid with 120 volts of power now applied to the liquid line solenoid. It then energizes and the plunger located inside of the liquid line solenoid valve body opens up which allows liquid refrigerant to flow through the valve body and into the metering device at the evaporator. As the refrigerant makes its way through the evaporator coil, our low side pressure now reaches above our cut in set point of 15 psi. This means that the contacts on the pressure controller will now close and set 120 volt power through the controller directly to one side of the contactor coil.

It completes our circuit and 208 volts is now being applied to our contactor coil. The contactor coil will then energize, pull in and send power through it to the compressor and condenser fan motors which now begin to operate with the compressor Now operational. High Pressure High Temperature Discharge Gas exits the compressor out of the discharge line and enters in at the top of the condenser coil as a 100 percent high pressure, high Temperature Vapor Refrigerant. As the refrigerant travels through the condenser coil, it will condense down and eventually leave through the bottom of the condenser coil As a hundred percent high pressure liquid refrigerant out of the bottom of the condenser coil, The liquid then enters into the inlet of the liquid line receiver.

The liquid run receiver is where excess refrigerant is stored for varying load conditions. The liquid refrigerant then exits out of the liquid line receiver and passes through a filter dryer. The filter dryer is installed to help absorb moisture and contamination that may be present in the system. You will typically see a liquid line sight glass installed after the filter dryer.

On most refrigeration systems, this is used as a visual indicator to ensure that we are receiving a full column of liquid to our expansion valve. Most sight glasses are typically equipped with a moisture indicator, further helping the technician determine if possible moisture and contamination issues are present within the system. It is worth noting though, that just because you have a flashing or bubbling sight glass, it does not always indicate you have a low uncharged scenario. Due to the system utilizing a liquid line receiver, sub cooling is not a reliable method of determining system charge, so proper steps should always be taken to ensure that no restrictions, heavy load or other issues are present in the system before adding charge.

When you see a flashing or bubbling sight glass, the refrigerant continues on through the liquid line until it reaches the expansion valve. As the refrigerant passes through the expansion valve, it flashes into a liquid Vapor mixture. This is where it proceeds to boil off as it passes through the evaporator coil and eventually leave at the top of the evaporator as a hundred percent low pressure low temperature vapor. The low pressure low temperature vapor is then returned to the compressor and the cycle will replace itself all over again.

When the system is satisfied or in defrost and no call for refrigeration is present, the thermostat's contacts will open, removing power from the liquid line solenoid and causing the liquid line solenoid to de-energize. The plunger located inside the liquid line solenoid valve body returns to the closed position, stopping the flow of liquid refrigerant into the evaporator coil. The liquid refrigerant that accumulates in the liquid line receiver where it is stored due to no refrigerant flowing through the evaporator coil on the low side of the system, the system begins its pump down procedure until it reaches the set cutout setting of 5. PSI Once it reaches a set cutout setting of the pressure controller, the contacts inside the pressure controller will open up, removing power to the contactor coil and turning off the compressor and condenser fan motors.

This is the basic working principles of an automatic pump down refrigeration system. Thank you for watching! Alright, just a reminder, Make sure to subscribe to official Bad TXV on Instagram and Bad TXV on Tick Tock in order to see more of the great videos that Corey does out in the field. Thanks for watching our video if you enjoyed it and got something out of it. If you wouldn't mind hitting the thumbs up button to like the video, subscribe to the channel and click the notifications Bell to be notified when new videos come out.

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