Impact of Airflow on Refrigerant Measurements and Performance

Impact of Airflow on Refrigerant Measurements and Performance

In this class, Bryan teaches the Kalos techs about airflow and how it impacts system performance. He explains the factors that affect airflow and how those contribute to the overall state of an HVAC system. We use training equipment and MeasureQuick to demonstrate these concepts.
By Bryan Orr

On a typical no-cooling call, many techs start with a visual inspection to look for restrictions. These techs will likely check the cleanliness of the filter, blower wheel, and evaporator coil inlet. Some techs also check the return grille, as it may be dirty or have an extra filter. Frozen evaporator coils are also a symptom of poor airflow (frozen evaporator coils also cause even worse airflow).

On the auditory side of inspection, listening for abnormal motor sounds can clue you in on the static pressure, especially when high static pressure affects ECM motors. Alternatively, strange motor noises can tell you about the motor or blower wheel’s health. For example, PSC motors won’t ramp up under high static pressure; abnormal noises indicate bearing wear or a loose hub on the blower wheel.

Customers may cause low airflow in their HVAC systems. For example, customers may close supply air vents to force more air into another room. (To force more air into rooms effectively, an HVAC contractor can cut a duct board so that it flexes and has a small hole, and then they’d insert it into the supply duct to act as a secondary damper. However, this practice may increase static pressure along the way and negatively affect airflow.) Customers may also move furniture in front of the return and obstruct airflow. Pet hair can also plug returns and filters.

Other causes of poor airflow include collapsed or disconnected ducts. Insulation in the unit can also suck up against the blower. (Don’t pull panels off while the unit is running to avoid letting the insulation cause a restriction.) Water in the return can also cause airflow restrictions, especially in flex duct systems. Fire dampers may cause poor airflow in commercial applications. Slipping belts or poorly adjusted sheaves can also contribute to poor airflow.

Before taking any measurements, make sure your gauges have been zeroed out and calibrated against each other. When you have poor airflow, your typical measurements will be either normal or low. You can expect your superheat to be normal to low. Your suction pressure, head pressure, and delta T will also be low. Static pressure is NOT a measure of airflow, but it can tell you about the airflow; you can have poor airflow if the static pressure is good, but the motor may not be producing enough airflow. However, the ULTIMATE indicator of low airflow is a low suction line temperature; any suction line temperature lower than 50 degrees (F) with normal indoor temperature is a likely indication of low airflow.

Some tools that measure airflow include TrueFlow grids, vane anemometers, and hot wire anemometers. However, these are advanced tools, and each one has its limitations. So, the best way to spot a system airflow problem is to perform those inspections with your senses and take your standard measurements.

As air moves over the evaporator coil, it comes into contact with the fins. Heat moves from the air to those fins, as heat moves from warm air to the colder fins. That heat transfer is critical for moving heat from a space, and fins help the evaporator maintain pressure.

When you have low airflow, the compressor amp draw will drop. The reduced pressure indicates that the refrigerant has less mass. The compressor does less work, but it doesn’t get cooled off as easily, and flooding is also possible.

In our class, we used the training equipment to simulate various low-airflow conditions. We also used the MeasureQuick app to profile the equipment, determine our ideal measurement ranges, and display our data. The MeasureQuick app determined that our superheat was hunting and that we were overfeeding our evaporator.

After troubleshooting the unit, we reduced our supply airflow. Our suction line pressure sharply decreased. We then jammed cardboard in the return duct, and our TESP sharply increased. Overall, our suction line temperature decreased sharply, TESP increased sharply, and subcooling increased slightly. MeasureQuick determined that we were running 249 CFM per ton, which indicates very low airflow.

Check out information on the 2022 HVACR Training Symposium HERE.

If you have an iPhone, subscribe to our podcast HERE, and if you have an Android phone, subscribe HERE.

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Most popular videos

See all +
thumbnail

Tips for Cleaning an Air Conditioning Common Drain

thumbnail

Gas Furnace Overview w/ AC Service Tech

thumbnail

Motor Overload and Safeties – Kalos Meeting

thumbnail

A Common Electrical Mistake

thumbnail

5 Traits of Bad HVAC Leaders

thumbnail

Don’t Overfill Refrigerant Recovery Cylinders The Easy Way

thumbnail

How to Replace an AC Condensing Fan Motor

thumbnail

How to Braze Air Conditioning Copper

thumbnail

How to Leak Test an AC With Nitrogen Pressure

thumbnail

How to Properly Pipe a Drain on a Fan Coil

thumbnail

4 Silly Mistakes of The Green HVAC Tech

thumbnail

How to Install an AC Disconnect

thumbnail

Why a Hard Shut Off TXV Closes

thumbnail

The Importance of SST (Evaporator Temperature) and Using a Scale (Kalos Meeting)

thumbnail

Adjusting Gas Pressure on a Standard and Gemini Furnace Valve

thumbnail

How a Heat Pump Reversing Valve Works

thumbnail

Don’t Confuse TD & Delta T

thumbnail

How to Install a Thermostat

thumbnail

How and When to Use a Schrader Core Removal Tool

thumbnail

Why Does The Evaporator Coil Freeze (And How to Diagnose It)

thumbnail

How to Measure Total External Static Pressure (TESP)

thumbnail

Does a TXV Shut under Vacuum?

thumbnail

Prevent this Common Manometer Mistake

thumbnail

Facts About Fusite (Compressor Electrical Pass Through Connections)

thumbnail

See Inside a Biflow/Heat Pump Filter Drier

thumbnail

Flammable Refrigerant Safety Basics – Kalos Meeting

thumbnail

Stuck Contactor Issue

thumbnail

How is 208 volts different than 230/240 volts?

thumbnail

Tips for Hiring & Getting Hired

thumbnail

Open vs. Closed Refrigeration

thumbnail

How is a 3-Phase Motor Different than Single Phase

thumbnail

HVAC Class 11/24/2020 – Electrical Review

thumbnail

How to Measure Gas Pressure – Kalos Meeting

thumbnail

What is Common, Start and Run?

thumbnail

Perfect Flares Every Time w/ NAVAC NEF6LM

thumbnail

Ask Bryan Anything Live Call-in from 11/21/2020

thumbnail

How to Build a Sheet Metal Coil Case From Scratch

thumbnail

What Air Filter is The Best?

thumbnail

Basic Electrical Circuit Terms

thumbnail

The #1 Key to Service Success?

thumbnail

How To Keep Motors Running Cool And Efficient

thumbnail

Talk Through The Refrigerant Circuit Using The “Glass Tube” trainer

thumbnail

Top 10 HVAC Tech Tips for 100K

thumbnail

Installing a Rectangle to Round Transition into an Existing Metal Duct

thumbnail

How Humidity Impacts The Weight of Air

thumbnail

Testing Home Pressure Imbalance w/ Genry Garcia (Spanish)

thumbnail

Some of Bryan’s Favorite New Tools Giveaway Meeting

thumbnail

Bert Teaches The Basic Refrigerant Circuit + Safety

thumbnail

Heat Rise Airflow Calculation

thumbnail

LIVE Apprentice Q&A

thumbnail

Setting a Refrigerant Charge by Subcool

thumbnail

The Toxic SUPER TECH Mindset

thumbnail

Soft Skills Can Be Hard (Disciplines of Growth)

thumbnail

Double Crimp Connection

thumbnail

How to Fabricate a Metal Supply Plenum From Scratch

thumbnail

Delivered Capacity Basics – Kalos Meeting

thumbnail

Sequencer Facts – They Aren’t All The Same

thumbnail

Wire Routing & Float Switch Positioning

thumbnail

Dual Voltage and Part Start 3-Phase Motors

thumbnail

Apprentice Program Day 1 – Using Your Resources w/ Jason Obrzut

thumbnail

Bert Cleans Out His DIRTY Work Van (And You Should Too!) #BERTLIFE

thumbnail

Liquid Line VS. Discharge Line

thumbnail

Tips for Proper AC System Cleaning – Kalos Meeting

thumbnail

EPA 608 Prep – Type 3

thumbnail

Motor Replacement Tips & Tricks – Kalos Meeting

thumbnail

EPA 608 Prep – Type 2

thumbnail

Better Duct Installation Practices – Kalos Meeting

thumbnail

THIS Is How My FIRST WEEK As An HVAC Apprentice Went (I’m Being Trained By WHO?!)

thumbnail

EPA 608 Prep – Type 1

thumbnail

How to Find Refrigerant Leaks – Kalos Meeting

thumbnail

Advanced Ventilation w/ CERV2

thumbnail

Critical System Diagnosis for Residential HVAC

thumbnail

Diagnosing Open & Short Circuits

thumbnail

Installing a Mitsubishi One-Way Ceiling Cassette In An Unfinished Room (You Can See EVERYTHING!)

thumbnail

How to Use a Blower Door (Como usar el Blower Door)

thumbnail

How to Stop Drain Snot (Bacterial Zoogloea)

thumbnail

EPA 608 Core Prep – Part 2

thumbnail

EPA 608 Core Prep – Part 1

thumbnail

A Strange Contactor Issue

thumbnail

GreenSpeed Extreme Install

thumbnail

Symptoms of Low Evaporator Airflow

thumbnail

Preventing Flooding On a Walk-In Call

thumbnail

Symptoms of Overcharge

thumbnail

Diagnosing and Replacing a Run Capacitor

thumbnail

Symptoms of Low Refrigerant Charge

thumbnail

Preventing, Finding & Repairing Refrigerant Leaks

thumbnail

Proper Use of Manometers for HVAC Technicians

thumbnail

UV light and Petri Dish Demo

thumbnail

Tool Talk Live – Probes, Bags, Hand Tools, Power Tools & More

thumbnail

Cleaning BARD units with Venom Packs

thumbnail

Electrical Basic Concepts – RSES NATE Prep

thumbnail

Selling, Upselling, IAQ , Hardstart Kits and More

thumbnail

Cutting & Installing a Rectangle Duct Connection

thumbnail

How to Make a Leak Free Canvas Duct Connector

thumbnail

Cooling Commissioning Measurements Walk Through w/ MeasureQuick

thumbnail

How to Checkout Blower Settings Using a Manometer

thumbnail

Recovery Best Practices & Giveaway

thumbnail

Introduction to the Fieldpiece Joblink Manometer Set

thumbnail

HVAC SCHOOL MONEY TALK – Don’t Make This Common Mistake

thumbnail

Testing out a High Performance HVAC Installation

thumbnail

Commercial Refrigerant Retrofit Options in a Crisis Economy #LIVE

thumbnail

HVAC Myth Busting #2 – Volts Go Down, Amps Go Up

thumbnail

Rectorseal RSH 50 Installation

thumbnail

Setting Up Residential Demand Ventilation with Laser Egg

thumbnail

Residential Zoning Talk #LIVE

thumbnail

DUCTLESS Control and Humidity Hack with Cielo Breez

thumbnail

HVAC Myths and Controversy #1

thumbnail

Rectorseal Surge Protector Installation

thumbnail

HVAC Contractors Guide to COVID-19

thumbnail

Commercial Install Review

thumbnail

DIY Cloth Mask with HEPA Pocket

thumbnail

How to Make an Indoor Air Cleaner the Cheap and Easy Way

thumbnail

Electrical Diagnostic Thinking

thumbnail

Human Comfort Basics – RSES NATE Prep

thumbnail

Introducing Venom Packs

thumbnail

5 Install Mistakes that Kill Systems

thumbnail

UV Part 2 – Honest UV Facts from a Manufacturer

thumbnail

UVC Air Purification – Live Podcast Part #1

thumbnail

How to Make a Metal Duct Transition in the Field

thumbnail

Reversing Valves (RSES NATE Prep)

thumbnail

Sunday Coil Cleaning #BERTLIFE

thumbnail

Liquid Line Solenoid on Long Refrigerant Lines

thumbnail

Condensing Unit Install Practices (RSES NATE Prep)

thumbnail

HVAC Motor Types (RSES NATE Prep)

thumbnail

Relative Humidity in the Supply Air Stream

thumbnail

Advanced Combustion Analysis (HVAC) w/ Jim Bergmann

thumbnail

Advanced MeasureQuick Diagnosis w/ Jim Bergmann

thumbnail

How to Flow Nitrogen While Brazing

thumbnail

Compressor Tear Down (Don Gillis / Trevor Matthews)

thumbnail

Compressor Facts and Troubleshooting (Don Gillis / Trevor Matthews)

thumbnail

CO2 101 (with Don Gillis)

thumbnail

Nikki Kreuger – The Dripping Point

thumbnail

Inside a Scroll Compressor

thumbnail

Troubleshoot a Grounded (Shorted to Ground) Compressor

thumbnail

Using Power Factor to Check Capacitors Under Load

thumbnail

Straight Cool Air Conditioning Schematic (Carrier)

thumbnail

Charging During Low Outdoor ambient w/ Charging Jacket

thumbnail

Recovery Machine Speed Race 🏁NAVAC NRDD Digital vs. Appion G5 Twin

thumbnail

Is There Mold in my Ducks! 🦆(Ducts)

thumbnail

Inside a Sequencer

thumbnail

A thermostat miswire and distracted diagnosis #BERTLIFE

thumbnail

Cleaning large coils with CoilPro

thumbnail

Smelly Ductless #SOLVED

thumbnail

Inductive Reactance in Real Life

thumbnail

50K Subscriber Special & Behind the Scenes Tour

thumbnail

Compressor Won’t Run Diagnosis

thumbnail

A Blower and Heat Strip Dangerous Mistake

thumbnail

How to adjust a TXV, TEV or TX Valve

thumbnail

5 HVAC/R Terms That Sound Worse Than They Are

thumbnail

Fieldpiece Joblink Firmware Update Demo

loading

To continue you need to agree to our terms.

The HVAC School site, podcast and daily tech tips
Made possible by Generous support from