What You'll Learn

• How to select heating mode in measureQuick and why the correct mode selection is critical
• How diagnostic targets reverse between cooling mode and heating mode (indoor coil becomes the condenser, outdoor coil becomes the evaporator)
• How to interpret superheat and subcooling readings when the refrigerant cycle is reversed
• How to handle defrost cycle interruptions and low-ambient measurement challenges
• When to test in heating mode vs. cooling mode on a service call

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 Heat Pump Heating Mode Probes for placement specifics.
• Knowledge: Familiarity with the Heat Pump Service Workflow (see G4) and superheat/subcooling fundamentals (see E3)
• Time: 10 minutes to read; 30-60 minutes for a heating mode diagnostic in the field

Why Heating Mode Testing Matters

Heat pumps now represent 47% of the residential HVAC market (full-year 2025 data, measureQuick V12 database). Nearly half of the systems technicians encounter can operate in heating mode, and many service complaints occur during winter. If you only test in cooling mode, you miss heating-specific faults: reversing valve leaks, defrost board failures, auxiliary heat staging problems, and low-ambient capacity shortfalls.

Heating mode reverses the refrigerant cycle. The indoor coil, which acts as the evaporator in cooling mode, becomes the condenser. The outdoor coil, which rejects heat in cooling, now absorbs heat from the outdoor air. Every measurement location and diagnostic target changes with this reversal. Selecting the wrong mode in the app produces inverted pass/fail results for every subsystem.

DR Richardson (Owner, Elephant Energy) found that data-driven commissioning and testing in heating mode was critical for Colorado's climate: "Not a single customer lost heat on the coldest night of the decade."

Step-by-Step Guide

Step 1: Confirm the System Is Operating in Heating Mode

Before opening the app, verify the heat pump is running in heating mode at the equipment.

At the thermostat:

• Set to HEAT or AUTO with heating call active
• The system should be producing warm supply air

At the outdoor unit:

• The outdoor coil is absorbing heat, so air blowing off the coil feels cool or cold (the opposite of cooling mode)
• The suction line (leaving the outdoor coil) is cold to the touch
• The liquid line (leaving the indoor coil) is warm

If you cannot determine the mode by touch, clamp a temperature probe on each refrigerant line at the outdoor unit. The cold line is always the suction side, regardless of mode.

[Visual Reference] Outdoor heat pump unit in heating mode with pipe clamp temperature probes attached. One clamp is on the suction line (the cold line leaving the outdoor coil, carrying low-pressure gas back to the compressor). The other clamp is on the liquid line (the warm line carrying subcooled liquid from the indoor coil to the outdoor metering device). In heating mode, the cold line at the outdoor unit is always the suction side.

Step 2: Select the Heating Mode Workflow

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

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 (or Test Out if you have already completed repairs)

Do not use the A/C or cooling workflow when the system is in heating mode. The heating workflow applies reversed diagnostic targets automatically. If you select the wrong workflow, subcooling and superheat targets, supply/return temperature expectations, and pressure ranges will all be inverted.

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

Tip: If you started from the cloud and the system has an existing project, the equipment profile carries forward. Verify the mode is set to Heating before proceeding.

Step 3: Understand the Reversed Refrigerant Cycle

In cooling mode, superheat is measured at the indoor coil (evaporator outlet) and subcooling at the outdoor coil (condenser outlet). In heating mode, those locations swap:

The diagnostic logic does not change. Low superheat still means the evaporator is flooded (possible overcharge or TXV stuck open). High superheat still means the evaporator is starved (undercharge, restriction, or low airflow across the evaporator). What changes is which coil is which.

measureQuick handles this reversal automatically when you select the Heat Pump: Heating workflow. The app relabels measurement points and recalculates targets for heating mode. Your job is to place probes on the correct lines and confirm the app is in the right mode.

Step 4: Deploy Probes for Heating Mode

Probe placement follows the same physical logic as cooling, but the thermal context is reversed.

You need 9+ physical probes for a valid Vitals Score in heating mode, the same threshold as cooling.

[Diagram] Heating mode probe placement at the outdoor unit and indoor unit. Outdoor (evaporator): suction line temp on the cold line leaving the outdoor coil, discharge line temp on the compressor output, outdoor ambient temp 3-5 ft away in shade, low-side pressure at the suction service port. Indoor (condenser): liquid line temp on the warm line leaving the indoor coil, supply air temp at the first supply register, return air temp at the return plenum, high-side pressure at the discharge service port. Static pressure taps in the supply and return ducts, same positions as cooling mode. 9+ physical probes required for a valid Vitals Score.

Step 5: Allow the System to Stabilize

Heat pump heating mode requires longer stabilization than cooling mode. Allow 15-20 minutes for readings to settle, compared to 10-15 minutes in cooling.

At lower outdoor temperatures, the compressor works harder and the refrigerant cycle takes longer to reach steady state. Watch the stability indicators on the Diagnostics screen. Do not save Test In or Test Out data until all readings are stable.

Jim Bergmann notes in the measureQuick training series: "It takes about seven to eight minutes to actually get stabilized" under normal conditions, but heating mode in cold weather can take longer.

Step 6: Handle Defrost Cycle Interruptions

When outdoor temperatures drop below approximately 40F, the system will periodically enter defrost mode. During defrost:

• The reversing valve temporarily switches to cooling mode to send hot refrigerant through the outdoor coil and melt accumulated ice
• The outdoor fan stops
• Pressures and temperatures swing dramatically
• Auxiliary heat may activate to maintain indoor comfort
• The cycle lasts 2-10 minutes

Do not capture or evaluate readings during a defrost cycle. Wait for defrost to complete, then allow another 5-10 minutes of stabilization before saving data.

If defrost cycles are occurring every 10-15 minutes, that may indicate a defrost board or sensor problem rather than normal operation. Normal defrost intervals range from 30-90 minutes depending on conditions and manufacturer settings.

Step 7: Evaluate Heating Mode Results

Once readings are stable, review the Diagnostics screen. Key heating-mode evaluation points:

Refrigerant charge:

• Subcooling is now measured at the indoor coil (condenser). Target range depends on metering device and manufacturer specs.
• Superheat is now measured at the outdoor coil (evaporator). For TXV systems, this should be in the 5-15F range. For piston systems, superheat targets vary with outdoor ambient temperature.

Temperature differential:

• Supply air should be warmer than return air. A typical heat pump produces 15-25F temperature rise across the indoor coil, depending on outdoor temperature and system capacity.
• At low outdoor temperatures (below 25-30F), the temperature rise from the heat pump alone decreases. Auxiliary heat may supplement.

Airflow:

• Static pressure over 0.5" WC indicates duct restriction, same as in cooling mode
• Low airflow in heating mode raises head pressure at the indoor coil (now the condenser), increasing subcooling and reducing efficiency

Save the Test In when you are satisfied that readings are stable and representative.

When to Test in Heating Mode vs. Cooling Mode

• Customer complaint is heating-related: Test in heating mode
• Customer complaint is cooling-related: Test in cooling mode
• Maintenance visit, no complaint: Test in the seasonal mode (heating in winter, cooling in summer)
• Suspect reversing valve problem: Test in both modes within the same project to compare
• Charge verification after repair: Test in the mode you used to diagnose the problem. If the system was low on charge, the charge deficit shows in both modes, but the targets differ.

Note that commissioning (verifying a new installation) should always be done in cooling mode per ACCA and manufacturer standards, because cooling mode provides more accurate charge assessment. Heating mode testing is for service calls and maintenance visits where the system is already in heating operation.

Video Walkthrough

• YouTube: (13 min) - Walks through the full heat pump heating gauge-up workflow, including probe deployment and diagnostic evaluation in heating mode

• YouTube: (30 min) - Explains why commissioning is done in cooling mode and when heating mode testing is appropriate for service visits

• YouTube: (80 min, HVAC Design Partners) - Covers heat pump standards, reversing valve verification, and real-world testing across modes

• YouTube: (25 min) - Discusses heat pump heating workflows and hybrid system considerations

Tips & Common Issues

My readings look wrong after selecting heating mode

Confirm you selected Heat Pump: Heating and not the A/C or cooling workflow. If the workflow mode is wrong, all targets are inverted. Exit the test, create a new one with the correct workflow, and start over.

Superheat is very high at the outdoor coil in cold weather

At low outdoor ambient temperatures, suction pressure drops and superheat increases naturally. This does not always indicate an undercharge. Compare your readings against the manufacturer's heating mode performance tables for the current outdoor temperature. Variable-speed systems may ramp compressor speed to compensate, which affects expected superheat.

The system enters defrost during my test

Wait for defrost to complete (2-10 minutes), then allow 5-10 minutes of restabilization. If you already saved a Test In during defrost, the data is unreliable. Run a new test after the system returns to steady-state heating.

Supply air temperature is lower than expected

Check whether auxiliary heat is activating. If it is not, and outdoor temperature is below 25-30F, the heat pump may simply be at the limit of its capacity. This is normal physics, not a fault. If auxiliary heat should be running but is not, check the thermostat staging configuration and the auxiliary heat contactor or relay.

Should I test in both modes on every visit?

Only if you have reason to suspect a mode-specific fault (reversing valve leak, defrost board failure). For routine maintenance, test in whichever mode the system is currently operating.

Related Articles

Prerequisites (complete these first):

• Heat Pump Service Workflow - Full Test In / Test Out service procedure for heat pumps
• Heat Pump Heating Mode Probes - Probe placement specifics for heating operation

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

• Cold Weather Charging - Charging refrigerant when outdoor temps are below 55F
• Reading Diagnostic Flags - Interpreting pass/fail and flag indicators
• HVAC Vitals Score - Understanding the composite score in heating mode

Related in the same domain:

• AC Service Workflow - Standard cooling mode service procedure
• Superheat & Subcooling in measureQuick - Fundamentals of charge assessment
• AI System Profiler - Equipment identification from data plate photos
• Understanding Diagnostic Screens - Navigating the diagnostics view

Need Help?

Contact measureQuick support: support@measurequick.com