Freezing in HVAC Systems 3D
July 26, 2023
In this 3D video, we look at the causes and effects of freezing in HVAC systems (buildup of frost or ice on the equipment).
Freezing in HVAC Systems 3D
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Water freezes at 32°F or 0°F. When a surface, such as an evaporator coil, is below water’s freezing point and contains moisture, frost or ice may form on that surface. In many cases, freezing in HVAC systems starts at the evaporator coil and works its way out; freezing can happen when the suction saturation temperature stays below 32°F for an extended period of time.
Some HVAC/R applications, such as commercial freezers and heat pumps in heating mode, need to operate under below-freezing conditions; the formation of frost or ice will hinder heat transfer over time, and periodic defrosting will be required. Evaporator coils in cooling mode should NOT freeze; when freezing happens, it will block system airflow. In general, evaporator coils will be about 35°F below the return air temperature.
The rate at which freezing occurs will depend on the amount of moisture in the air, the length of time at which the evaporator coil temperature is below freezing, the temperature of the return air, the air velocity, and the overall coil design.
When you encounter a frozen system, allow it to defrost completely before troubleshooting. You may allow the system to defrost by leaving it off with (or sometimes without) the blower running. In some cases, you may be able to use a heat gun or run the heat pump in heating mode for a short period. Be mindful of the water as the ice melts and take steps to prevent water damage.
A low evaporator coil temperature may be caused by low load (low airflow and/or low indoor temperature), refrigerant undercharge, low outdoor ambient temperatures, blower issues, and refrigerant side restrictions. We can prevent low load by advising customers not to set their thermostats below 72°F in cooling mode on standard equipment. We can also prevent low airflow from being a factor by making sure we replace dirty filters and clean the evaporator coil and blower wheels as necessary. When freezing happens due to a low refrigerant charge or a restriction, we may also notice high superheat; in humid climates, freezing of this nature can cause the entire system to freeze up.
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Comments
Slightly off topic, I apologize. However, I've been reviewing all your videos and podcasts for discussion of EEV's. I'd like to see a tutorial/lecture/video (any of the above…:-) ) that discusses the consequences on gauge (pressures hi-lo side/temperatures hi-lo side) measurements when an EEV and an inverter driven compressor are present in a system. In other words: I understand how to diagnose problems when the system uses a fixed orifice, I'm pretty comfortable with diagnosis activities when the system uses a TXV….. but the emergence of EEV's and throttling compressors is making the interpretation of gauge readings a bit more confusing to me…. I suspect other techs are having difficulty here too. Any pointers ? Are you thinking of preparing a "back to basics" video for these modern Air Conditioning Systems? (Think Mitsubishi/Trane for example….)? Thanks for all you do, it is absolutely amazing!!!!…. I look forward to your response…. Thanks -Skip- tfsbj7@gmail.com
Slightly off topic, I apologize. However, I've been reviewing all your videos and podcasts for discussion of EEV's. I'd like to see a tutorial/lecture/video (any of the above…:-) ) that discusses the consequences on gauge (pressures hi-lo side/temperatures hi-lo side) measurements when an EEV and an inverter driven compressor are present in a system. In other words: I understand how to diagnose problems when the system uses a fixed orifice, I'm pretty comfortable with diagnosis activities when the system uses a TXV….. but the emergence of EEV's and throttling compressors is making the interpretation of gauge readings a bit more confusing to me…. I suspect other techs are having difficulty here too. Any pointers ? Are you thinking of preparing a "back to basics" video for these modern Air Conditioning Systems? (Think Mitsubishi/Trane for example….)? Thanks for all you do, it is absolutely amazing!!!!…. I look forward to your response…. Thanks -Skip- tfsbj7@gmail.com
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Hi Skip,
I can completely relate to feeling confused about how to interpret refrigerant pressures on systems with EEVs and Inverters. I can’t say that I have all the answers but I have two pieces of advice. If the equipment is one of the major US brands (trane, lennox, carrier, goodman) and it has an inverter, there is typically a check charge mode that you can access through the thermostat. At that point you can diagnose it like a traditional system. if there is a problem with the EEV, you’re going to have to dig into the manufacturer’s literature to follow their diagnostic procedure.
If you’re working on a mini split, I recommend getting a copy of Craig Migliaccio’s “Inverter Mini Split Operation and Service.” It’s the only book I know of that handles mini splits as a whole, vs. a brand specific approach. This book may help you understand how mini splits ramp up and down, and how they behave when they are running with low charge, high charge, etc.
I hope that helps
Hi Skip,
I can completely relate to feeling confused about how to interpret refrigerant pressures on systems with EEVs and Inverters. I can’t say that I have all the answers but I have two pieces of advice. If the equipment is one of the major US brands (trane, lennox, carrier, goodman) and it has an inverter, there is typically a check charge mode that you can access through the thermostat. At that point you can diagnose it like a traditional system. if there is a problem with the EEV, you’re going to have to dig into the manufacturer’s literature to follow their diagnostic procedure.
If you’re working on a mini split, I recommend getting a copy of Craig Migliaccio’s “Inverter Mini Split Operation and Service.” It’s the only book I know of that handles mini splits as a whole, vs. a brand specific approach. This book may help you understand how mini splits ramp up and down, and how they behave when they are running with low charge, high charge, etc.
I hope that helps
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