Hybrid HWT Diagnostic Tool
Created by Danny G.

Diagnostic Reference Guide

Thermistor Readings

Get Room Temp with Thermometer, Get Water Temp from Controller

  1. Hold MODE and NEXT — you should get TST
  2. Press the DOWN arrow until CP appears
  3. Press Enter and wait for display to show CP ON (Compressor On)
  4. Press Enter, enter reading for DT Temp (Discharge)
  5. Press Enter, enter reading for ST Temp (Suction)
  6. Press Enter, enter reading for ET Temp (Evaporator)
  7. Press Enter, enter reading for AT Temp (Ambient)
  8. Press Enter, enter reading for ST Temp
  9. Press Enter, enter reading for Current (CURR)
  10. Repeat steps again
Element Readings
  1. Hold MODE and NEXT — you should get TST
  2. Press the UP arrow once, UE is displayed
  3. Press Enter, enter UT Tank Temp (Upper Tank Temp)
  4. Press Enter button twice, wait for current to stabilize, enter reading for UE CURR (Upper Element Current)
  5. Hold MODE and NEXT — you should get TST
  6. Press the UP arrow twice, LE is displayed
  7. Press Enter, enter LT Tank Temp (Lower Tank Temp)
  8. Press Enter button twice, wait for current to stabilize, enter reading for LE CURR (Lower Element Current)
Ideal Temperatures
Sensor Range Notes
DT – Discharge Less than 160°F Should increase 10–15°F between tests
ET – Evaporator Less than 70°F
ST – Suction 38°F – 90°F
Next Steps
  • If one temperature reading is excessively high while others fluctuate normally — recheck the affected Thermistor, no further testing required.
  • If all temperatures remain close to AT with no fluctuation — proceed to test the Expansion and Compressor.
  • If DT and ET remain close and decrease in temperature — inspect installation and venting.
How to Test the Capacitor
  1. Remove Controller, locate Capacitor (left corner)
  2. Verify Capacitor has 1 Purple wire and 2 Red wires
  3. Hold MODE and NEXT — you should get TST
  4. Press DOWN arrow until CP is displayed, wait for CP ON
  5. Test across the terminals of the Capacitor for VAC while Compressor is running (highest voltage range)
Capacitor Results
  • If wiring is not correct — update it and rerun the heat pump reading test.
  • If voltage is above incoming power (208/240 VAC) but below 310 VAC — replace the capacitor.
  • If voltage is below incoming power (208/240 VAC) — call back for next steps.
  • If voltage is above 310 VAC — this is considered normal. Continue to test the EXV and Compressor.
Compressor Resistance Testing

Test resistance between the following points and enter readings:

TestPoints
AYellow wire → Red wire
BYellow wire → Purple wire
CRed wire → Purple wire
How to Test the EXV — Keep Power OFF

Locate the 5-pin EXV wiring harness and pull the clip out. On the back of the wire harness plugged into the control board, there are silver contacts that can be used as test points.

Test resistance (ohms) on the following combinations:

CombinationReference Ohms
Orange → Yellow87.6 Ω
Red → Black88.2 Ω
Grey → Black44.7 Ω
Grey → Yellow87.6 Ω
Grey → Red43.9 Ω
Grey → Orange44.3 Ω
Technician Edition
Temps
Thermistors
Heating Elements
Capacitor
Compressor
Compressor To Ground
EXV