What You'll Learn

• How to determine whether to test in cooling mode or heating mode based on season and thermostat settings
• How to select the correct measureQuick workflow for a heat pump service call
• How to run a Test In / Test Out paired workflow on a heat pump
• How probe placement and diagnostic targets change between cooling mode and heating mode
• How to diagnose reversing valve problems using mode-dependent superheat and subcooling patterns
• How to handle defrost cycle interruptions during heating-mode testing
• How to evaluate auxiliary heat staging and when strip heat activation indicates a problem

What You'll Need

• Device: iPhone (iOS 15+) or Android phone (Android 10+) with measureQuick v3.5+
• Account: Premier Services subscription (required for Guided Workflows)
• Tools: 9+ physical probe channels (temperature clamps, pressure probes, psychrometer, manometer). See Outdoor Probe Placement and Heat Pump Heating Diagnostics for placement details.
• Knowledge: Familiarity with the AC Service Workflow (see G2) and heat pump installation workflow (see G3). Understanding of superheat and subcooling (see E3).
• Time: 15 minutes to read; 45-90 minutes for a complete Test In / Test Out service call

Why Heat Pump Service Differs from A/C Service

A heat pump uses the same refrigerant cycle as an air conditioner, but it reverses direction to provide heating. On a service call, you must account for the current operating mode before you start.

In cooling mode, the outdoor coil is the condenser and the indoor coil is the evaporator. In heating mode, that flips: the outdoor coil becomes the evaporator and the indoor coil becomes the condenser. Superheat and subcooling measurement locations reverse with it. If you set up probes or select a workflow based on the wrong mode, the diagnostic targets will be inverted and every pass/fail result will be unreliable.

Heat pump service also introduces failure modes that do not exist on standard A/C systems: reversing valve failures, defrost board malfunctions, and auxiliary heat staging problems. The Test In / Test Out paired approach from the AC Service Workflow applies here, with additional diagnostic checkpoints for these heat-pump-specific issues.

DR Richardson (Owner, Elephant Energy) found that measureQuick's data-driven approach was critical for verifying heat pump performance during extreme cold, reporting that "not a single customer lost heat on the coldest night of the decade" thanks to the combination of commissioning data and remote monitoring. Kyle Ricciardi (Owner, AC Authority) notes that guided workflows save time on every service call: "The first day I used guided workflows, I shaved off 10 minutes of a full project."

Step-by-Step Guide

Step 1: Determine the Operating Mode

Before selecting a workflow or placing probes, confirm which mode the heat pump is running in.

Check the thermostat:

• Set to COOL or AUTO with cooling active = cooling mode
• Set to HEAT or EMERGENCY HEAT = heating mode
• Set to AUTO with heating active = heating mode

Verify at the equipment:

• In cooling mode, the suction line (large copper line between outdoor and indoor unit) is cold, and the liquid line (small copper line) is warm
• In heating mode, the suction line is cold at the outdoor unit, and the liquid line leaving the indoor coil is warm

If you are unsure, clamp a temperature probe on each line at the outdoor unit. The cold line is always the suction side (evaporator outlet), regardless of mode.

Tip: On a service call, test in whichever mode the customer is using. If the complaint is "no heat," test in heating mode. If the complaint is "not cooling," test in cooling mode. If the system has problems in both modes, run separate tests for each mode within the same project.

Step 2: Select the Correct Workflow

Open measureQuick. Create a new project or open the existing one for this customer.

For cooling mode:

1. Tap New Test
2. Select A/C or Heat Pump Service / Maintenance
3. In the system profile, set System Type to Heat Pump
4. Set the workflow phase to Test In

This is the same workflow you use for standard A/C service. The heat pump distinction is in the profile, not the workflow selection.

For heating mode:

1. Tap New Test
2. Select Heat Pump: Heating
3. In the system profile, confirm System Type is Heat Pump and Mode is Heating
4. Set the workflow phase to Test In

The heating workflow applies reversed diagnostic targets automatically. Do not use the A/C or cooling workflow when testing in heating mode.

Workflow selection screen showing Heat Pump Heating Test option in the Heating Projects section

Step 3: Profile the System

Use the AI System Profiler to scan the outdoor unit nameplate (see AI System Profiler). Verify these fields after the scan:

• Manufacturer and model - confirms equipment identity
• Refrigerant - R410A is most common; R22 on older units; R454B or R32 on newer installations
• Tonnage - from the outdoor unit rating plate
• Metering device - heat pumps typically use TXV on both coils, but older systems may have a fixed orifice on one side
• SEER/CTOA - confirm the efficiency range

If you are in heating mode, also confirm:

• Supplemental heat type - electric strip heat or gas furnace backup
• Expected temperature rise - from the manufacturer's specifications

Tip: If the customer's complaint involves one mode but not the other, still profile the full system. The profile carries across both cooling and heating tests within the same project.

Step 4: Deploy Probes

Probe placement depends on the operating mode.

Cooling mode probe placement (same as standard A/C):

Heating mode probe placement (reversed refrigerant context):

The physical probes are the same instruments. What changes is which line carries suction gas and which carries subcooled liquid. If you are confused about which is which in heating mode, temperature tells you: the cold line at the outdoor unit is always suction.

[Diagram] Heat pump heating mode probe placement. The cold line at the outdoor unit is always the suction line (evaporator outlet), and the warm line is the liquid line (condenser outlet from the indoor coil). Suction pressure connects at the outdoor service port; discharge pressure connects at the indoor side. Temperature clamps go on the suction line leaving the outdoor coil and the liquid line leaving the indoor coil. Static pressure taps remain in the same duct positions as cooling mode.

Step 5: Run the Test In

Start the system and allow it to stabilize. The stabilization period depends on the mode:

• Cooling mode: 10-15 minutes, same as A/C
• Heating mode: 15-20 minutes. Heat pumps in heating mode produce lower temperature differentials than A/C systems in cooling, and stabilization takes longer, especially at lower outdoor temperatures

Watch the stability indicators on the Diagnostics screen. Do not evaluate results until readings settle.

Heating mode caution: If the outdoor temperature is below 40F, the system may enter a defrost cycle during your test. Defrost temporarily reverses the system to cooling mode to melt ice from the outdoor coil. During defrost:

• Pressures and temperatures shift dramatically
• The outdoor fan may stop
• Auxiliary heat may activate to maintain indoor comfort
• The cycle lasts 2-10 minutes

Wait for defrost to complete and the system to return to normal heating operation. Allow another 5-10 minutes of stabilization after defrost before capturing your Test In readings.

Once readings are stable, review the Diagnostics screen. Tap each subsystem to examine the detail views (see Understanding Diagnostic Screens). Document the current condition.

Save the Test In. The app records the workflow phase as test_in.

Diagnostics screen during heat pump heating Test In, showing pass/fail indicators for heating-mode subsystems

Step 6: Diagnose and Repair

With the Test In complete, you have a documented baseline of the system's current condition. Identify the failures and perform repairs.

Common heat pump service findings and their diagnostic signatures:

Refrigerant charge problems:

• High superheat (piston systems) or low subcooling (TXV systems) = undercharge
• Low superheat or high subcooling = overcharge
• Same interpretation in both modes; the measurement location changes, but the diagnostic logic is identical

Reversing valve issues:

• A stuck or leaking reversing valve produces different symptoms depending on which mode you test in
• If the valve leaks internally, refrigerant bypasses the valve, reducing efficiency in one mode more than the other
• Symptom: normal superheat/subcooling in cooling mode but abnormal readings in heating mode (or vice versa). If charge diagnostics pass cleanly in one mode but fail in the other with no other explanation, suspect the reversing valve.

Defrost board problems:

• Excessive defrost cycles (every 10-15 minutes) waste energy and prevent the system from maintaining heating output
• Insufficient defrost (ice buildup on outdoor coil) restricts airflow across the outdoor coil, increasing suction superheat and reducing capacity
• Check the outdoor coil for ice accumulation. If ice persists after a defrost cycle, the defrost sensor, timer, or control board may be faulty.

Auxiliary heat staging:

• Electric strip heat (emergency heat) activating when the heat pump compressor is running normally indicates a staging problem
• Common causes: thermostat configured for too narrow a differential, outdoor lockout temperature set too high, or a control board forcing auxiliary heat unnecessarily
• Check the supply air temperature rise. If the rise exceeds what the heat pump alone can produce (typically 15-25F depending on outdoor temp), auxiliary heat is contributing.

Airflow issues:

• Static pressure over 0.5" WC indicates duct restriction, same as A/C service
• In heating mode, low airflow across the indoor coil (now acting as the condenser) raises head pressure and subcooling

Step 7: Run the Test Out

After completing repairs, restart the system and allow it to stabilize again. Use the same stabilization guidelines from Step 5.

1. Create a new test within the same project
2. Select the same workflow you used for the Test In
3. Set the workflow phase to Test Out
4. Verify the system profile matches the Test In (the app carries the profile forward within the project)
5. Confirm probes are still in position and transmitting

Once stable, review the Diagnostics screen. Compare Test Out results against the Test In baseline.

Save the Test Out. The app records the workflow phase as test_out.

What to look for in the comparison:

• Failed subsystems from the Test In should now pass (or move closer to target)
• Refrigerant charge readings should be within the acceptable range
• Supply/return temperature differential should match expectations for the mode
• Vitals Score should improve from Test In to Test Out

[Visual Reference] Test In and Test Out results displayed together after service. The Test In baseline shows the original condition (e.g., failed refrigerant charge, low Vitals Score). The Test Out shows post-service improvement: subsystems that previously failed now pass, refrigerant readings are within target, temperature split has improved, and the Vitals Score is higher. The paired comparison documents the value of the work performed.

Step 8: Document and Close

The project now contains a paired Test In / Test Out record. This documentation serves multiple purposes:

• Proves the system condition before and after your work
• Supports warranty claims if the equipment is under manufacturer warranty
• Provides a baseline for future service visits (the next technician can compare against today's Test Out)
• Generates customer-facing reports with the Vitals Score improvement

If the system has problems in both cooling and heating modes, run a second pair of tests in the other mode. Save all tests within the same project. Each test records its mode (cooling or heating) and workflow phase (test_in or test_out) independently.

Heating vs Cooling: Quick Reference

Low Ambient Heating Performance

As outdoor temperature drops, heat pump heating capacity and efficiency decrease. This is inherent to the technology, not a system fault.

Approximate performance expectations:

At low outdoor temperatures, auxiliary heat is expected to supplement the heat pump. If the customer reports "not enough heat" and the outdoor temperature is below 25-30F, check whether auxiliary heat is activating as designed before diagnosing a heat pump problem.

Variable-speed heat pumps perform better at low ambient than single-stage units. They maintain higher capacity by increasing compressor speed as outdoor temperature drops. For variable-speed systems, confirm the unit is modulating upward in response to the load before concluding there is a capacity deficit.

Transcript Insights

Jim Bergmann describes the heat pump service context in his Part 4 walkthrough: "in there maybe you're on a maintenance, maybe you're on a service call, but either way you're going to want to inspect components down in there." The service workflow applies whether the call is reactive (customer complaint) or proactive (maintenance visit).

On the importance of proper commissioning as the prerequisite for effective service diagnostics, Jim notes in the Cooling Commissioning walkthrough: "commissioned correctly, you really can't do much of a good diagnostic, right? I mean, it's all about, does each system sort of operate properly." A system that was never properly commissioned will show diagnostic failures on a service call that may not indicate a new problem, but rather an original installation deficiency.

From the Benchmarking video, Jim explains why benchmarked systems make return service visits more efficient: "this is really the most powerful feature of measureQuick because it baselines your company, so everybody knows exactly how a piece of equipment is supposed to operate." When a previous technician benchmarked the system during commissioning, the return service visit starts with known targets rather than generic defaults.

Customer Insights

• Aaron Gregg (Service Manager, Jacob's Ladder Heating and Cooling, 3 service techs): "It's just like having the senior tech right there beside you telling you why your superheat is too high." His junior techs use the diagnostic flags during heat pump service calls to identify issues they would otherwise miss. He also uses remote streaming to help junior techs from another job site.

• Chad Simpson (Owner, Simpson Salute, ~100 employees): "He was three months in the field and diagnosed that as well as one of our 20-year vet technicians would have." For heat pump service, where the reversed cycle adds complexity, the guided workflow keeps entry-level technicians on track.

• Matt Krewer (Service Manager, Town & Country Services): "We found things that other companies overlooked because they just didn't have the setup. That gave us a lifetime customer." He specifically notes that whole-system grading (rather than single-part replacement) catches issues like reversing valve problems and airflow restrictions that would otherwise be missed.

Video Walkthrough

• YouTube: (13 min). Walks through the heat pump heating gauge-up workflow, including probe deployment, stabilization timing, and diagnostic evaluation. Demonstrates the distinction between the non-invasive test and the full gauge-up test for service visits

• YouTube: (1,390 views, 8 min). Covers heat pump mode detection and full diagnostics, including non-invasive techniques for maintenance visits where gauging up is not warranted

• YouTube: (80 min, HVAC Design Partners). Covers heat pump commissioning standards, reversing valve verification, and real-world TrueFlow testing. Relevant to service calls where you need to compare current performance against commissioning baselines

• YouTube: (21,950 views, 1:41). Short demonstration of heating mode probe placement at the outdoor and indoor units

• YouTube: (14 min). Step-by-step walkthrough of heating mode workflows, including probe placement and diagnostic target interpretation

• YouTube: (18,992 views, 53 min). Advanced diagnostic techniques applicable to heat pump service, including fault isolation and result interpretation

• YouTube: (9,324 views, 18:40). Variable-speed heat pump testing, profiling, and diagnostic interpretation for service calls

• YouTube: (6:40). Shows how a prior commissioning benchmark provides locked-in targets for return service visits, so technicians know "exactly how a piece of equipment is supposed to operate" without re-deriving targets

Tips & Common Issues

I am unsure whether the system is in heating or cooling mode

Clamp a temperature probe on each refrigerant line at the outdoor unit. The cold line is the suction side. In cooling mode, the large (suction) line going to the indoor unit is cold. In heating mode, the line leaving the outdoor coil is cold. If the outdoor fan is running and the coil is rejecting heat (you feel warm air), the system is in cooling mode. If the coil is absorbing heat (air feels cool or cold), the system is in heating mode.

Defrost cycle interrupted my test readings

This is normal below approximately 40F outdoor temperature. Wait for the defrost to finish (2-10 minutes), then allow 5-10 minutes for the system to restabilize in heating mode. Do not capture final Test In or Test Out readings during or immediately after a defrost cycle.

Superheat is normal in cooling but high in heating (or vice versa)

This pattern points to a reversing valve leak. When the reversing valve does not seal completely, hot discharge gas bleeds into the suction side. The leak may be more pronounced in one direction than the other, producing acceptable readings in one mode and abnormal readings in the other. Measure the temperature of the reversing valve body; a significant temperature gradient across the valve body during operation suggests internal leakage.

Auxiliary heat runs constantly even when the heat pump compressor is operating

Check the thermostat staging configuration. Many thermostats allow you to set the temperature differential that triggers auxiliary heat (often called "compressor-to-aux differential" or "second stage lockout"). If this differential is too narrow (1-2F), the strips will activate during normal operation. A typical setting is 2-3F differential with a 15-30 minute delay before auxiliary heat engages. Also check the outdoor lockout temperature; if it is set above the current outdoor temp, auxiliary heat may be forced on by design.

The Vitals Score did not improve after repairs

Confirm that the system has fully stabilized (15-20 minutes in heating mode). If the score is still low, check each failing subsystem individually. A common oversight: repairing the refrigerant charge but not addressing an airflow restriction (high static pressure). Both must pass for the Vitals Score to reflect a healthy system.

Should I test in both modes on every service call?

Not necessarily. Test in the mode relevant to the customer's complaint and the current season. If the complaint is heating-specific, test in heating mode. If you discover a reversing valve issue or a charge problem that may affect both modes, running a second test in the other mode documents the full picture. For maintenance visits with no specific complaint, testing in the seasonal mode (cooling in summer, heating in winter) is standard practice.

The system is a dual-fuel hybrid (heat pump + gas furnace)

Run two separate workflows. Test the heat pump in its current mode using the appropriate heat pump workflow. Test the gas furnace using the Gas Furnace workflow. Save both test sets within the same project. See Hybrid System Workflow for the full procedure.

How do I handle a variable-speed heat pump on a service call?

Force the system to full design capacity before capturing measurements. Use the manufacturer's test mode or set the thermostat to maximum differential. Variable-speed heat pumps modulate to match the load, so readings at partial capacity will not match design targets. See Equipment Types in measureQuick for test mode procedures.

Reference Material

Download: Field Checklists Combined (PDF)

Related Articles

Prerequisites (complete these first):

• AC Service Workflow - Test In / Test Out paired approach
• Heat Pump Installation - Heat pump profiling and mode-specific setup

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

• Hybrid System Workflow - Dual-fuel heat pump + gas furnace testing
• Reading Diagnostic Flags
• mQ Assist (AI Diagnostics)
• HVAC Vitals Score - Understanding and presenting the composite score

Related in the same domain:

• AI System Profiler
• Equipment Types in measureQuick
• Superheat & Subcooling in measureQuick
• Heat Pump Heating Diagnostics - Probe requirements for heating mode
• Understanding Diagnostic Screens

Need Help?

Contact measureQuick support: support@measurequick.com