Every diagnostic calculation in measureQuick depends on the system profile. The profile tells the app what kind of equipment is installed, how it was designed to operate, and what targets to evaluate against. When the profile is accurate, the diagnostics are accurate. When it is wrong, the diagnostics are wrong.
There are a small number of adjustable parameters in the system profile and diagnostic screens. Each one controls a specific part of the diagnostic math. This article covers each parameter: what it does, where to find it, what the default is, when to change it, and what goes wrong if it is set incorrectly.
Getting these parameters right matters. As Jim Bergmann explains: "the design temperature difference or condenser temp over ambient was ambient plus 30 degrees" for older equipment, but modern high-SEER systems operate at lower temperature differences. From the mQ V12 database of 115,706 quality-filtered cooling tests, 56.0% of piston systems fail the charge evaluation. Some portion of those failures reflect genuinely undercharged or overcharged systems, but incorrect profile parameters (wrong SEER, wrong metering device, wrong refrigerant) also contribute to false diagnoses.
Refrigerant type determines the pressure-temperature (P/T) relationship curve used for all saturation temperature calculations. Every superheat and subcooling value in the app depends on this setting.
In the system profile setup screen. Refrigerant type is one of the first fields you set when creating or editing a profile.
No default. You must select the refrigerant type for the system you are testing.
| Refrigerant | Typical Application |
|---|---|
| R410A | Standard residential A/C and heat pumps (2010-present) |
| R22 | Legacy systems (pre-2010 installs, declining in field) |
| R454B | Newer replacement for R410A (2025+) |
| R32 | High-efficiency systems, common in ductless/mini-splits |
Always confirm the refrigerant type matches the equipment data plate. Do not assume R410A on every system. R22 systems are still in service, and R454B is entering the market.
Every saturation temperature calculation will be incorrect. Superheat and subcooling readings will be off by several degrees, sometimes by 10F or more. The app will flag charge faults that do not exist, or miss real charge problems. This is the single most damaging parameter to get wrong.
Tip: Check the outdoor unit data plate. The refrigerant type is printed there. If the system has been converted (for example, R22 to a drop-in replacement), confirm what refrigerant is actually in the system, not what the data plate says.
System capacity in tons. Tonnage feeds the airflow target calculation: the app multiplies tons by your CFM/ton setting to determine how much airflow the system needs.
In the system profile, under equipment specifications. If you use the AI System Profiler (see D1), it reads tonnage from the model number. If you build the profile manually, you enter it directly.
Populated from the model number when using the AI Profiler. No default for manual entry.
Residential systems: 1.5, 2, 2.5, 3, 3.5, 4, 5 tons.
Verify the tonnage matches the actual equipment. Pay attention to oversized evaporator configurations: a 3-ton condenser paired with a 3.5-ton evaporator coil is a 3-ton system for diagnostic purposes (the condenser sets the capacity). See High Efficiency/Oversized Evaporator for these scenarios.
Airflow targets scale directly with tonnage. A 3-ton system at 400 CFM/ton expects 1,200 CFM. If you enter 2 tons, the app expects 800 CFM. Your airflow diagnostics will be incorrect, which cascades into capacity calculations and the Vitals Score.
The airflow rate per ton of cooling capacity used to calculate the system's target CFM. This is the design intent for the duct system, not a measured value.
In the system profile. Look for the Design Airflow or CFM/ton field. In the Brian Feenie demo walkthrough, this appears at approximately 6:15 on the system profile screen.
400 CFM/ton.
300-500 CFM/ton.
Adjust based on climate and system design:
| Climate/Condition | Recommended CFM/ton | Reason |
|---|---|---|
| Hot and humid (Gulf Coast, Southeast) | 350 CFM/ton | Lower airflow drops supply air temperature, increasing dehumidification |
| Moderate/mixed | 400 CFM/ton | Standard design assumption for most residential systems |
| Hot and dry (Southwest, arid) | 425-450 CFM/ton | Higher airflow maximizes sensible cooling where humidity is not a concern |
| Manufacturer-specified | Per spec | Some equipment manuals specify a CFM/ton value; use it |
The app calculates target airflow as: Target CFM = Tonnage x CFM/ton.
If CFM/ton is set too high, the app expects more airflow than the system was designed to deliver. The airflow subsystem will flag a false failure. If CFM/ton is set too low, the app will accept inadequate airflow as passing.
The airflow target also feeds into superheat and subcooling target calculations. Wrong airflow assumptions compound into wrong charge diagnostics.
Tip: When in doubt, leave it at 400 CFM/ton. This is the industry standard assumption and produces reasonable diagnostics for the majority of residential systems. Only adjust it when you have a specific reason.
The Seasonal Energy Efficiency Ratio of the system. In measureQuick, the SEER rating drives the CTOA (Condensing Temperature Over Ambient) calculation. Higher SEER equipment operates with a lower temperature difference between the condensing temperature and the outdoor ambient air.
In the system profile, under Efficiency Standard. In the demo walkthrough, this appears at approximately 6:17. You select a SEER range, and the app shows the corresponding CTOA.
Varies by system. The AI Profiler attempts to determine SEER from the model number. For manual profiles, you select it.
| SEER Range | CTOA |
|---|---|
| 6-9 SEER (Older than 1991) | 30.0 F |
| 10-12 SEER (1992-2005) | 25.0 F |
| 13-16 SEER (2006-present) | 20.0 F |
| 17+ SEER (2006-present) | 15.0 F |
These are the four discrete buckets the app uses. CTOA is the expected difference between the condensing temperature (saturation temperature at the high-pressure side) and the outdoor ambient temperature. A 10-12 SEER system running with 95F outdoor air should have a condensing temperature around 120F. A 17+ SEER system in the same conditions should condense around 110F.
Set SEER to match the outdoor unit's rated efficiency. This is printed on the data plate or available from the manufacturer's specifications. Do not guess. If you cannot determine the SEER rating, err toward the lower end (13-14 SEER for older equipment, 14-16 for post-2015).
Wrong SEER means wrong CTOA. Wrong CTOA shifts the expected condensing temperature. This directly affects the subcooling calculation and the charge diagnostic.
Example: A 20 SEER system has a real CTOA of about 18F. If you set the profile to 13 SEER (CTOA 30F), the app expects a condensing temperature 12F higher than reality. The app will interpret the actual (correct) condensing temperature as too low and may flag an undercharge that does not exist.
This is one of the most common sources of false charge diagnoses in the field.
The expected temperature difference between the condensing saturation temperature and the outdoor ambient air temperature. CTOA is the bridge between efficiency rating and charge diagnostics.
In the system profile, linked to the SEER selection. When you select a SEER range, the app calculates and displays the corresponding CTOA. On the demo walkthrough, this appears at approximately 6:21.
Derived from the SEER rating you select. See the SEER-to-CTOA table above.
In most cases, let the SEER selection drive the CTOA automatically. Only override the CTOA directly if you have manufacturer documentation that specifies a different CTOA for the exact unit you are testing. Some manufacturers publish CTOA values in their engineering data that differ slightly from the SEER-based approximation.
Same impact as wrong SEER: the expected condensing temperature shifts, producing incorrect subcooling targets and false charge diagnoses. If the CTOA is too high, the app expects a higher condensing temperature and may miss an overcharge. If the CTOA is too low, the app expects a lower condensing temperature and may flag a false undercharge.
The type of metering device in the system determines the primary diagnostic approach for refrigerant charge evaluation. As Jim Bergmann demonstrates in his walkthrough: "I set the type of metering device - thermostatic expansion valve, piston, capillary tube, electronic expansion valve, or automatic expansion valve." measureQuick supports all five types, though residential systems are predominantly TXV or piston.
In the system profile, under Metering Device. In the demo walkthrough, this appears at approximately 6:23.
No default. You must select the metering device type for the system.
Always match the actual metering device in the system. Check the indoor coil (evaporator) data plate or installation documentation. If you see a TXV body on the liquid line entering the evaporator coil, select TXV. If there is no TXV and the system uses a piston or capillary tube, select Fixed Orifice/Piston.
Setting TXV when the system has a piston means the app evaluates charge by subcooling and largely ignores superheat as a charge indicator. On a piston system, subcooling alone does not reliably indicate charge state, so the app may miss a charge problem.
Setting piston when the system has a TXV means the app evaluates charge by superheat. A functioning TXV actively controls superheat, so the superheat will appear normal regardless of charge level, and the app will report the charge as acceptable when it may not be.
This parameter changes the entire diagnostic logic. Getting it wrong can produce a clean diagnostic report on a system with a significant charge problem.
Tip: When in doubt, physically inspect the evaporator coil. A TXV has a sensing bulb clamped to the suction line near the evaporator outlet. A piston system has no bulb; the metering device is inside the coil distributor.
The expected subcooling value for the system, in degrees Fahrenheit. Subcooling is the temperature difference between the actual liquid line temperature and the condensing saturation temperature. The target represents proper charge level for TXV-equipped systems.
In the system profile under charge parameters. In the demo walkthrough, charge parameters appear at approximately 6:35.
Varies by equipment. The app uses a standard default based on the system profile. Typical residential defaults fall in the 8-14F range.
Change it when you have the manufacturer's specified subcooling target for the exact condenser you are testing. This is printed on the condenser data plate or in the installation manual. Common manufacturer targets:
| Manufacturer/Situation | Typical Subcooling Target |
|---|---|
| Most residential condensers | 10-12F |
| Some Carrier/Bryant models | 8-10F |
| Some Lennox models | 12-14F |
| Per data plate | Use the exact value printed |
Always use the manufacturer's specified value when available. It accounts for the specific condenser coil design and intended refrigerant volume.
If the subcooling target is set too high, the app expects more subcooling than the system is designed to produce. A properly charged system will appear undercharged, and a technician following the diagnostics will add refrigerant, overcharging the system.
If the subcooling target is set too low, the app accepts less subcooling than the system needs. An overcharged system may appear acceptable.
Each degree of subcooling target error shifts the charge diagnostic by roughly one degree of measurement tolerance. A 3-4F error in the target can flip a pass to a fail or vice versa.
The expected superheat value for the system, in degrees Fahrenheit. For piston/fixed orifice systems, superheat is the primary charge indicator. For TXV systems, superheat is controlled by the valve and is less relevant to charge diagnostics.
In the system profile under charge parameters, near the subcooling target.
For piston systems, the app calculates the target superheat from operating conditions: outdoor ambient temperature and indoor wet bulb temperature. This is the standard charging chart method. The calculated target typically falls between 5F and 25F depending on conditions.
For TXV systems, the app uses a nominal superheat reference (typically 10-12F) since the TXV controls superheat mechanically.
For piston systems, the calculated target is usually correct. Override it only if the manufacturer publishes a specific superheat target that differs from the standard charging chart calculation for the conditions you are testing in.
For TXV systems, superheat adjustment is rarely necessary because the TXV regulates it independently of charge level.
On a piston system, a wrong superheat target produces the same kind of cascade as a wrong subcooling target: the charge diagnostic evaluates against the wrong benchmark, and the pass/fail result may not reflect actual charge state.
On a TXV system, the superheat target has less diagnostic impact because charge is evaluated through subcooling. However, a significantly wrong superheat target can still affect supplementary diagnostic flags.
| Parameter | Location | Default | Typical Range | When to Adjust | Risk if Wrong |
|---|---|---|---|---|---|
| Refrigerant Type | System Profile | None (must select) | R410A, R22, R454B, R32 | Always verify against data plate | All saturation temps wrong; false charge diagnosis |
| Tonnage | System Profile | From model number (AI) or manual entry | 1.5-5 tons | Verify against data plate; use condenser rating for oversized evap | Airflow targets and capacity calculations wrong |
| Design Airflow (CFM/ton) | System Profile | 400 | 300-500 | Humid climate: 350; dry climate: 450; per manufacturer spec | Airflow pass/fail and charge targets shift |
| SEER Rating | System Profile (Efficiency) | Varies | 13-25+ | Match outdoor unit rated efficiency | Wrong CTOA; false charge diagnosis |
| CTOA | Derived from SEER | Auto-calculated | 15-30F | Only if manufacturer specifies a different CTOA | Expected condensing temp shifts; charge diagnosis wrong |
| Metering Device | System Profile | None (must select) | TXV or Piston/Fixed Orifice | Always match actual equipment | Entire diagnostic approach wrong; misses real charge faults |
| Subcooling Target | Charge Parameters | 8-14F (varies) | 8-14F | When manufacturer data plate specifies a target | Over/undercharge diagnosis off by target error margin |
| Superheat Target | Charge Parameters | Calculated from conditions (piston) | 5-25F | Rarely; only if manufacturer specifies differently | Piston charge diagnosis off; less impact on TXV systems |
These parameters do not work in isolation. They form a chain of dependent calculations:
Getting any single parameter wrong shifts the diagnostic output. Getting two or more wrong can produce results that appear internally consistent but are entirely misleading. This is why profile verification (see Profile Verification) is a critical step before interpreting diagnostics.
YouTube (HVAC School): (18,030 views, 1:55). Covers how compression ratio, capacity, and efficiency interact with system profile parameters. Includes discussion of static pressure, refrigerant behavior, airflow, and system profiling
YouTube (HVAC School): (15,014 views, 1:41). Common charging errors that result from incorrect profile parameters, covering refrigerant selection, metering device, system profiling, and probe placement
YouTube: (4,695 views, 9:22). Explains how parameters feed into the diagnostic calculations and what the app does with each setting
YouTube: (9,324 views, 18:40). Demonstrates parameter adjustment for high-efficiency systems where SEER, CTOA, and CFM/ton deviate from standard residential defaults
YouTube: (18,992 views, 53 min). Jim Bergmann discusses parameter tuning for accurate diagnostics, including CTOA selection and metering device implications
YouTube: (15,726 views, 45 min). End-to-end commissioning walkthrough that includes system profile setup and parameter selection
Check your SEER rating and CTOA first. This is the most common cause of false charge flags. If the SEER is set too low for a high-efficiency system, the app expects a higher condensing temperature than the system actually produces. Correct the SEER, and the charge diagnostic will update.
The AI Profiler reads the model number from a photo. It correctly identifies tonnage and refrigerant type in most cases, but it may not always determine the exact SEER rating or metering device type. Verify those two parameters manually after the profiler runs. See Profile Verification.
Check the outdoor unit data plate. If it only lists EER (not SEER), you can approximate: SEER is typically 1.1-1.2x the EER for single-stage equipment. If the data plate is unreadable, look up the model number on the manufacturer's website or the AHRI directory (ahridirectory.org). As a last resort, estimate based on equipment age: pre-2006 equipment is likely 10-13 SEER; 2006-2015 is likely 13-16 SEER; post-2015 is likely 14-20+ SEER.
Physically inspect the liquid line where it enters the evaporator coil. A TXV has a valve body (brass or steel, larger than the liquid line) and a sensing bulb clamped to the suction line near the evaporator outlet, usually insulated with tape or foam. A piston system has no external valve body; the metering device is a small brass fitting or disc inside the coil's distributor assembly. If you still cannot determine the metering device, check the evaporator coil's model number and look up the specifications.
For piston systems, the calculated superheat target depends on outdoor ambient temperature and indoor wet bulb temperature. Verify that both of these readings are accurate. If the outdoor temperature probe is in direct sunlight or near the condenser discharge air, it will read high and shift the superheat target. If the indoor wet bulb reading is incorrect (probe not in the airstream, or in a dry location), the target calculation will be off.
When the system is installed in a hot, humid climate where the design intent is to maximize dehumidification. Lowering CFM/ton drops the supply air temperature, pulling more moisture out of the air. Common in the Gulf Coast states, Florida, and similar climates. Some equipment manufacturers specify 350 CFM/ton for their humidity-optimized systems. Do not drop below 300 CFM/ton; this risks evaporator coil icing.
Start with refrigerant type. Confirm it is correct, then move to metering device, then SEER/CTOA, then airflow. Fix them in that order, because each downstream parameter depends on the ones above it.
Prerequisites (complete these first):
Follow-up articles (next steps after this one):
Related in the same domain:
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