Lack of A/C Performance in High Ambient Temperatures

The air conditioning system may be blowing warm air on some 2017-2019 Colorado and Canyon models. In some cases, the A/C evaporator may be freezing up. There also may be a lack of air flow from some of the vents.

The lack of A/C performance may be due to the A/C system being used on the coldest temperature setting with the fan control set to the lowest speed setting. (Fig. 14) These conditions typically occur in climates with a high ambient temperature (over 85°F or 29°C) and humidity over 80 percent.


Fig. 14


If these conditions are found, follow the A/C diagnostic procedures in the appropriate Service Information. If the conditions cannot be corrected following the Service Information, a Service Only calibration change has been released in TIS2Web for this specific A/C performance concern.

TIP: Be sure to follow the Service Information A/C Performance diagnostic procedures first before any reprogramming is attempted.


Unique Calibration

If it’s determined that reprogramming is necessary, reprogram the H33 HVAC Control Module with the calibration available in TIS2Web with the SPS description: “Refer to TSB #19-NA-177 – Special Use Only. To reduce evaporator freeze-up in hot, extreme humid environments, such as gulf coast states. Not to be used in any other condition or environment due to some negative effects on cabin comfort.”

Use of this calibration should be accompanied with an explanation that an increase in the temperature cycling of the system will be noted. The air output at the vents will vary higher or lower by a couple degrees as the cabin is cooled and will be most notable when the outside temperature and the set point of the system are similar.

For additional information, refer to Bulletin #19-NA-177.


– Thanks to Matt Singer

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