Tag: refrigeration

I was watching this video on the HVACR Videos channel by my friend Chris Stephens and I was impressed by how completely he diagnoses the system both visually and with his tools. Take a look.

I say this all the time, but a good, efficient technician is one who sees everything and can also quickly diagnose the main thing

First off… and this isn’t shown in the video. Chris knows what type of appliance this is, what sequence of operation it runs in and how the controls work. He likely knows all of this because he has a ton of experience on these freezers. If he didn’t then the first course of action would be to do a bit of reading up on the manufacturer’s site or app so that you have the basics before proceeding.

So let’s explore everything Chris found and how he found it

  • Failed door seal
  • Dirty Condenser Coil
  • Frozen Evaporator Coil
  • Defrost Heater inoperable
  • Failed Defrost Limit

The main thing wrong with this machine is a failed defrost limit but Chris was able to diagnose the problem quickly because he used these skills of perception –

  • Cycling a defrost mode (prior knowledge of the equipment or reading the manual)
  • Noticing how quickly the suction line froze (visual and touch)
  • Visual observation of the frozen coil (visual)
  • Looking at the wiring diagram to find the circuit (Diagram reading)
  • Testing for voltage to the defrost heater (electrical diagnosis)
  • Measuring amperage on the heater circuit to see if it is working (electrical diagnosis)
  • Looking at the diagram again and finding a limit inline (diagram Reading)
  • Finding the high limit failed open (electrical diagnosis)

In addition to these efficient diagnosis skills, Chris was thinking about –

  • Proper authorization for repair (getting approval before defrost)
  • Protecting the equipment and workspace (covering the control with a bag)
  • Noting and quoting other repairs needed for optimum performance (condenser coil cleaning, door seal)

These additional diagnosis items for optimum performance took no additional time and will result in a more profitable repair ticket and a piece of equipment that will run better, with lower power consumption and less likelihood of an expensive callback.

You will notice that his first instinct wasn’t to hook up gauges or use fancy tools. In this case, he really didn’t need them and it would have only wasted time. When he returns he will make the repairs and observe temperatures only to gauge the progress of the machine to ensure it’s going to get to and maintain temperature.

In refrigeration, especially small refrigeration like this you need to think about –

  • Coil cleanliness (Condenser & evaporator)
  • Fan and compressor operation (is everything running when it should and going off when it should)
  • Defrost type and function (is it coming in and out of defrost)
  • Product and boxes aren’t in the way of proper condenser or evap airflow
  • Door seals are in good shape
  • Door fits properly and hinges aren’t bent or damaged
  • Box achieves and maintains the proper temperature for the product contained within

Of course, there is a time to connect gauges or probes and refrigeration is no exception, but the best techs use their senses first, knowledge of the equipment or reading second and their tools only once they know exactly what they are looking for.

Great job Chris! and I would suggest subscribing to his channel HERE

— Bryan

 

This article is written by Christopher Stephens of JVS Refrigeration in California with just a few additions by me (Bryan) in italics. Thanks, Chris!


Reach in refrigerators are an interesting side of our industry, often looked at as frustrating and troublesome. Often working in kitchens or convenience stores the refrigerators are never located in a convenient place to work on them, and that tends to lead to frustration on the technician’s part. Please understand my article pertains to medium temperature refrigerators. I also advise you to use manufacturers OEM parts when possible as the unit was designed to work with them. One of the more misunderstood and misdiagnosed parts is the temperature controller.

Keep in mind that some refrigeration temperature controls sense the evaporator coil temperature (not the desired box temperature) some use intake air sensors and some use supply air sensors. The medium being sensed (Coil, return air (intake) or supply air (discharge) will greatly impact how the controls function and what impacts them.

Personally, I break temperature controllers down into five different types, please understand that these are generic descriptions and you should always lean on the manufacturer if possible to understand their control strategies. 

  1. Standard Pressure Control – these work on the principle that at any given pressure saturated refrigerant is a constant temperature. This style of control is not used very much anymore as a means of temperature control because it is not very precise and to an untrained technician, it can be hard to set the temperature correctly.To use this control strategy, you need to understand what evaporator T.D. (Temperature differential) your reach-in was designed with, you will need a temperature pressure chart, you will need an accurate set of refrigeration gauges, and an accurate thermometer. With all these tools you can take your desired box temperature and find it on your pressure chart read across the pressure chart and find the corresponding pressure for your desired box temperature and that will be your cut-in pressure to set your control at. Now we need to find the cut-out setting typically we want the system to have about a 5-8 degree differential between the cut out and cut in to reduce system short cycling this will likely be about 8 degrees colder than the cut-in temperature, so take your desired box temperature subtract your differential of 5-8 then subtract your designed evaporator T.D. (specific to the equipment but likely 20 -30 degrees for reach ins) and find that number on the temperature pressure chart than read across the pressure chart and find the corresponding pressure and that will be your cut out setting.  Understand that pressure controls are never exact, so you will need to adjust accordingly in the field.
  2. Constant Cut in Control (electromechanical) – These are one of the most common temperature control’s that you will find in reach in refrigerators because they are the most economical for the manufacturers as they have an off cycle defrost built into them. They work by inserting the sensing bulb into the evaporator coil and they have a set temperature that they turn back on (cut in) at no matter how cold you turn the dial. They work very similar to the pressure control as they are designed with the evaporator T.D. (Temperature Differential) in mind, but instead of using pressure they sense the evaporator temp on the surface of the coil, they do have a knob to adjust the cut-out temperature, but you have no control over the cut in temperature that is why they are called constant cut in. By design they also have a built-in defrost as the cut in temperature is usually 37 to 41 degrees (for a cooler/refrigerator) depending on the manufacturer. They rely heavily on proper superheat and proper refrigerant charge. If the charge is incorrect or the superheat is not correct the coil could get too cold and the control could prematurely shut off. This could lead a technician to diagnose a bad control if they did not understand how they work.  If you come upon a reach in that is short cycling and shutting off too soon, make sure to check the charge and measure the evaporator superheat before you diagnose a bad control.
  1. Constant cut in (Digital) – These work the same as the electromechanical control, but they typically have two probes one to be located in the coil and one to be located in the return air stream. They tend to have more features that are available, such as an added defrost cycle based off time (every four hours, every six hours, etc.…..)  while still using box temperature as a fail-safe. For example, say the control has a defrost every four hours if the coil temperature comes above a pre-determined temp say 40 degrees the control will terminate the defrost. The controls can also shut off the evaporator fan motors during the off cycle to save energy and reduce warm is intrusion into the unit. These types of controls are on many HC (Hydrocarbon) units being built today.
  2. Universal electromechanical – these typically have one sensing bulb that you mount in the return air stream and they turn on and off via the temp setting.
  3. Universal digital – These are usually aftermarket controls and can have several different control strategies and can usually be customized to do anything, from heating to cooling to defrost depending on the manufacturer.

 

Something to understand is that reach in refrigerators is usually designed to perform in a certain environment and if something changes such as the ambient temp in that environment, or if doors are left open. The box will not perform correctly, I suggest you take a step back before you start throwing parts at a reach in and evaluate the environment you may find your problem there!

— Chris

As always I suggest “Commercial Refrigeration for Air Conditioning Technicians” by Dick Wirz as the bible for refrigeration training 


I don’t do much in the way of “rack” refrigeration, but I recently had a conversation with experienced rack refrigeration tech Jeremy Smith and he got me thinking about EPR valves.

I’ve heard EPR (Evaporator pressure regulator) valves called suction regulators or hold back valves. In essence they hold back against the suction line to maintain a set evaporator evaporation or boiling temperature.

In refrigeration rack systems EPR valves play a vital role in ensuring that the product is cooled consistently and nearly constantly.

In an A/C system we have a TXV that maintains a constant superheat at the evaporator outlet. The evaporator temperature itself will fluctuate up and down depending on load.

In a refrigeration case you must first ensure you have full line of liquid using a sight glass or by checking subcooling. Then you make sure the case has proper airflow etc… then you set the EPR to maintain the proper coil evaporation temperature (by holding back pressure as needed) and then you check and / or set the TXV to the proper superheat. This ensures BOTH proper coil feeding as well as proper coil temperature.

Pretty cool right? (Pun intended)

— Bryan

refrigeration_for_AC_Techs

In this episode of HVAC School Bryan talks with Jeremy Smith and they discuss

  • Reznor startup
  • Being on call in the refrigeration world
  • differences and similarities between rack refrigeration and A/C
  • Hot gas and electric defrost
  • Glycol refrigeration systems
  • Subcool and Superheat
  • Refrigeration TXV settings
  • EPR valves and their settings
  • Rack manifold pressure

And Much more…

As always if you have an iPhone subscribe HERE and if you have an Android phone subscribe HERE

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