What You'll Learn

• How measureQuick classifies diagnostic faults into severity levels
• The difference between minor faults (single measurements slightly out of range) and major faults (significant deviations or compounding issues)
• How fault aggregation works across multiple measurements
• The 19 pass/fail (pf_) subsystems and what each evaluates
• What override flags mean and how they affect reported failure rates
• Why subjective subsystems (condensate, outdoor, indoor, air filtration) should be interpreted differently from measurement-based subsystems
• How to read fault indicators on the diagnostic screen and in reports

What You'll Need

• Device: iPhone (iOS 15+) or Android phone (Android 10+) with measureQuick installed
• Account: measureQuick account with active subscription
• Familiarity: Comfort navigating the measureQuick diagnostic screen (see Understanding Diagnostic Screens)
• Time: 10 minutes to read; ongoing reference during field diagnostics

How measureQuick Classifies Faults

measureQuick does not simply report raw numbers. It evaluates each measurement against target ranges specific to the equipment, operating conditions, and refrigerant type. When a measurement falls outside its acceptable range, measureQuick flags it. But not all out-of-range readings carry the same weight.

The app uses a multi-level severity system:

Flag Colors on the Diagnostic Screen

These flags appear on individual measurements in the diagnostic screen. A single yellow flag on one reading is informational. Multiple yellow flags on related measurements, or any red or black flag, warrants investigation.

measureQuick diagnostic screen showing a mix of green, yellow, and red flag indicators across different measurements

Minor Faults

A minor fault occurs when a single measurement is slightly outside its target range. Examples:

• Subcooling 1-2 degrees above target when all other refrigerant measurements are within range
• Return air temperature slightly below the expected range in mild outdoor conditions
• Supply static pressure at 0.52" on equipment rated for 0.50"

A minor fault on its own may not indicate a real problem. Measurement tolerances, sensor accuracy, and changing conditions (a cloud passing over the condenser, a door opening in the house) can push a reading slightly out of range temporarily.

measureQuick displays minor faults as yellow flags. They serve as awareness indicators, not necessarily action items.

When a Minor Fault Matters

A single minor fault becomes significant when:

• It persists after the system has stabilized (7-8 minutes of run time)
• It appears alongside other minor faults that point to the same root cause
• It contradicts what the rest of the measurements suggest

For example, subcooling slightly high plus superheat slightly low plus suction pressure slightly high - each individually minor - together suggest the system is overcharged. No single measurement crosses a critical threshold, but the pattern is clear.

Major Faults

A major fault indicates a significant deviation from the expected operating range, or a combination of minor faults that together point to a real issue. Examples:

• Superheat at 35F on a system targeting 12F - the evaporator is starved for refrigerant
• TESP at 0.85" on equipment rated for 0.50" - severe airflow restriction
• Discharge temperature exceeding manufacturer limits - compressor stress
• CO levels above safe thresholds during combustion analysis - safety concern

Major faults appear as red flags or black flags on the diagnostic screen. They require action: further investigation, repair, or at minimum, documentation and customer communication.

measureQuick also performs fault aggregation, analyzing relationships between measurements rather than evaluating each in isolation. This is what separates mQ from basic digital gauge readouts. A gauge shows you a number. measureQuick tells you what that number means in context.

As Jim Bergmann demonstrates in the Benchmarking video, measureQuick clears faults when the root cause is addressed. After correcting airflow on a benchmarked system, "there's no system-wide issues detected" because the underlying readings all moved into their target zones.

The 19 Pass/Fail Subsystems

measureQuick evaluates system performance through 19 subsystems, each with its own pass/fail determination. Every subsystem has two associated values in the test record:

• pf_{subsystem}_result: The final pass or fail determination (Pass, Fail, or NULL if not evaluated)
• pf_{subsystem}_override: Whether the technician changed the result (1 = overridden, 0 = app determination accepted)

The subsystems cover:

Measurement-Based Subsystems

These are evaluated using live instrument data:

• Electrical system - voltage, amperage, power factor
• Air distribution - total external static pressure, airflow
• Refrigerant charge - superheat, subcooling, pressures
• Venting system - draft, CO, stack temperature, combustion efficiency
• Gas piping - manifold pressure, gas supply pressure
• Temperature performance - temperature split, supply/return relationships

These subsystems have objective measurement thresholds. When a measurement exceeds the threshold, the subsystem fails. Failure rates from these subsystems are reliable indicators of real conditions in the field.

Subjective Subsystems

Four subsystems are based on visual inspection rather than instrument measurement:

• Condensate - drain line condition, pan condition
• Outdoor unit - physical condition, clearances, cleanliness
• Indoor unit - physical condition, cleanliness
• Air filtration - filter condition, fit, MERV rating appropriateness

These subsystems appear on the diagnostic screen and in subsystem reviews, but they rely on the technician's judgment rather than instrument readings. The override rate for these subjective subsystems is approximately 95% - meaning technicians change the app's default result nearly every time.

This high override rate does not mean the subsystems are broken. It means the app defaults to a conservative position (prompting review), and technicians confirm or adjust based on what they see. When analyzing failure rates across a fleet or a dataset, subjective subsystems should be reported separately from measurement-based subsystems to avoid inflating or deflating overall failure rates.

Understanding Overrides

When a technician changes a subsystem's pass/fail result, the override flag (pf_{subsystem}_override) is set to 1. This means:

• The headline failure rate for any subsystem in reports or analytics is the post-override rate - the rate after technicians have applied their judgment
• The pre-override rate (what the app determined before technician input) reflects the app's raw analysis
• Override is not "cheating" - it is the designed workflow. measureQuick is built so the app provides an initial assessment and the technician confirms or adjusts

For example, the app may flag a refrigerant charge subsystem as "Fail" because subcooling is 2 degrees above the target range. The technician, knowing the system just cycled on and readings have not fully stabilized, may override to "Pass" with the intention of rechecking after stabilization. The override records that decision.

Reading Faults on the Diagnostic Screen

The measureQuick diagnostic screen presents faults at two levels:

Individual Measurement Level

Each measurement (superheat, subcooling, TESP, discharge temp, etc.) shows its own indicator:

• The current value
• The target range
• A color-coded flag (green, yellow, red, or black)

System Level

At the top of the diagnostic view, measureQuick summarizes the overall system status. If no system-wide issues are detected, it displays a clean status. If faults are present, it identifies the most significant ones.

As shown in the Benchmarking workflow, after clearing a low-load fault on the evaporator, the system-wide summary updated to "no system-wide issues detected." The individual fault (low evaporator load) was resolved, and the system-level assessment reflected the change.

Diagnostic screen showing system-level summary with active faults and individual measurement flag indicators

Fault Classification in Practice

Here is how to think about fault levels during a service call:

1. All green flags: System is operating within acceptable ranges. Document the results and generate the report.

2. One or two yellow flags: Note them. Check whether the system has stabilized. If the flags persist after 7-8 minutes of run time, investigate further. If they resolve, they were likely transient.

3. Multiple yellow flags pointing to the same root cause: Treat as a significant finding even though no individual measurement has crossed a critical threshold. Investigate the root cause.

4. Any red flag: This is a real issue. Investigate, diagnose, and communicate to the customer with supporting data from the measureQuick report.

5. Any black flag: Critical. Address immediately, especially for safety-related measurements (CO levels, gas leak detection).

Video Walkthrough

• YouTube (measureQuick): (4,695 views, 9:22). How measureQuick's diagnostic engine works internally, including fault classification and the relationship between individual measurements and system-level assessments

• YouTube (measureQuick): (view count varies). Demonstrates how faults appear and clear during a benchmarking workflow, including the "no system-wide issues detected" state after resolving a low evaporator load fault

• YouTube (third-party): (13,085 views, 80 min). Detailed explanation of flag colors: "black flag that's a critical problem, caution triangle, red flag, yellow flag, but we're really looking to get that green flag."

• YouTube (third-party): . Discussion of fault prevalence: "systems all out there have at least one detectable fault" and how measureQuick identifies them

Tips & Common Issues

I overrode a subsystem by mistake

You can change the override back. Return to the subsystem review screen, tap the subsystem, and set it to the correct result. The override flag tracks the most recent change.

Should I override a failing refrigerant charge subsystem if I am about to add charge?

No. Save the test-in first with the failing result. Then perform your repair (add/remove charge, fix the leak, etc.). Run a test-out after the repair. The test-in/test-out comparison shows the before and after, which is the strongest documentation you can provide to the customer.

Why do subjective subsystems default to a certain result?

measureQuick prompts you to review these subsystems even though it cannot measure them with instruments. The default depends on whether you have entered any observations. If you skip the visual inspection, the subsystem may remain in a "not evaluated" or default-fail state to remind you to check it.

How do faults affect the Vitals Score?

Each failing subsystem reduces the Vitals Score. The score is a 0-100 composite based on how many subsystems pass and how far out of range the failing measurements are. A system with one minor fault will score higher than a system with multiple major faults. For details on Vitals Score calculation, see Understanding the Vitals Score.

Reference Material

Download: Field Checklists Combined (PDF)

Related Articles

Prerequisites (complete these first):

• Understanding Diagnostic Screens - How to navigate and read the diagnostic interface

Follow-up articles (next steps after this one):

• mQ Assist (AI Diagnostics) - Context-aware guidance that considers fault relationships
• Understanding the Vitals Score - How faults translate into the 0-100 system health score
• Component Pressure Drops - Diagnosing specific airflow faults

Related in the same domain:

• Reading Target Zones - Understanding the acceptable ranges that define pass/fail
• Interpreting Refrigerant Diagnostics - Fault patterns specific to refrigerant charge issues

Need Help?

If you get stuck or this article does not answer your question:

• Check the Related Articles section above
• Contact measureQuick support: support@measurequick.com
• Schedule a training session with the measureQuick training team