Some 2024-2026 Silverado EV, Sierra EV; 2025-2026 ESCALADE IQ, OPTIQ, Equinox EV, HUMMER EV; and 2026 ESCALADE IQL models may have inadequate cabin heating or cooling along with a Service High Voltage System and/or Maximum Charge Level is Limited message on the Driver Information Center. DTCs P0534 (Air Conditioning Refrigerant Charge Low) and B3A6F (Air Conditioning Refrigerant Flow Performance) may be set.
The conditions may be due to an internally failed evaporator check valve, where the valve internals may dislodge and affect thermal performance. Here’s a check valve without (left) and with the internal components (right) shown. (Fig. 6)
Fig. 6
To diagnose this issue, shift the vehicle to Propulsion mode and, using GDS, confirm the ambient air temperature sensor signal is above 15°C (59°F), which will indicate the vehicle is operating in cabin cooling mode.
Next, run only the first-row HVAC. Turn off the second- and third-row (if equipped) HVAC controls. Set the temperature to Low, the blower speed to Max, and the air distribution to Vent mode.
Verify the compressor is running by checking that the air conditioning compressor motor speed signal is above zero. Also verify that the evaporator EXV is open, indicated by the air conditioning evaporator electronic expansion valve feedback signal being above zero.
Check Parameters
If the compressor is running, run the test for five minutes and check the following parameters:
- Air conditioning refrigerant temperature sensor 5 signal is within +/- 5°C (41°F) of the ambient air temperature sensor signal.
- Air conditioning refrigerant temperature sensor signal is below 0°C (32°F).
If these parameters are met, the evaporator check valve is either installed backwards or broken and must be replaced. If the parameters are not met and DTCs P0534 and B3A6F are still set, refer to the diagnostics in the appropriate Service Information.
TIP: Take care when handling the check valve. Internal parts of the check valve may have fallen out. Look for all internal parts of the check valve (Fig. 7) If any check valve internals are missing, the A/C receiver/dehydrator bottle will require replacement along with a system flush.
Fig. 7
A/C Receiver/Dehydrator Bottle
On 2025 Equinox EV and OPTIQ models with a failed check valve, see Bulletin #26-NA-163 first. If the vehicle has not received the updated A/C receiver/dehydrator bottle, follow the procedures in the bulletin. A new check valve is included with the A/C evaporator line assembly. When installing the new A/C receiver/dehydrator, align it as shown. (Fig. 8)
Fig. 8
When installing the new dehydrator bottle to the bracket, align the bottle as shown for ease of installation. Do not fully tighten any connections until all lines have been aligned.
For more details, including part numbers, refer to Bulletin #26-NA-229.
– Thanks to Mark Shearer and Kayla Battaglia
