HVAC Air stops flowing from vents after 30 min. of travel.

ID Status Date Year Make Model Transmission Type A/C Controls Public/Private
#15560 In Progress 2013 Chevy Table public

2013 Chevy Tahoe LTZ, automatic controls. I have replaced the blower motor and blower motor resistor. After roughly 30-60 minutes on the road air stops flowing from the vents. I can hear the blower working, my assumption is that the blend creator is closing off the doors. If I turn the system off for 30 minutes and turn back on (while still traveling) air will flow. Should I just replace the blend actuator? I feel like I’m just throwing parts at it.

Sparky

It sounds like the evaporator core may be icing over. The next time it happens pull over, leave the engine running, open the hood and check for heavy frost on the a/c refrigerant lines. Especially near the firewall on the passenger side of the vehicle. If they are frozen, locate the A/C compressor relay in the underhood fuse box. Using a screwdriver handle or other blunt and slightly heavy tool to tap on the relay to see if the compressor turns off. If it turns off and the frost starts to clear the relay is the likely cause of the problem and should be replaced. Generally there will be more relays in the fuse box with the same part number on it. Locate a relay for a less important system such as the washer pump or horn and swap it with the a/c relay to see if the problem corrects.

If tapping on the relay makes no difference, remove the relay and note whether the compressor turns off. If it turns off, slowly reinstall the relay while carefully feeling for a click in the relay as the compressor turns back on. If there is no click and the compressor turns on the relay is stuck internally and swap it as noted above. If there is a click in the relay as the compressor engages, then there is something wrong with the control side of the system.

Has the a/c control panel been replaced  in the recent past?

The A/C Panel has not been replaced that I’m aware of. I’m hoping to recreate this incident today and check for evaporator core icing.

Happened this morning about 20 minutes into my trip. I pulled off the highway and the condenser was completely white and frozen over. I switched the condenser and fog light relays. On my next trip it cut out again but not as bad as before. Maybe just low on Freon?

Sparky

Refrigerant level is not the problem. You see that in residential systems but not automotive. There is a control issue that is keeping the compressor engaged and allowing the evaporator core to ice over. You can’t force/flow air through solid ice.

The reason I asked if the control panel may have been replaced is because your truck uses a evaporator core thermistor that signals the computer to turn the a/c compressor relay off before the evaporator ices up. New control panels sometimes have to be programmed before this system works correctly. So that would leave us with a likely fault with the evaporator temperature sensor/thermistor. Have you owned the truck since new or at least long enough that you know the system has operated correctly in the past?

I have owned the truck over 3 years. This issue did not occur early in ownership, but has occurred in the past year or so. It doesn’t affect us much as our daily travel rarely exceeds 30min of travel. So, we only notice it whole traveling out of town. I appreciate your responses and will look into the evaporator temperature sensor/thermistor.

Sparky

In the meantime I would recommend turning the compressor off for a minute or two every ten to twenty minutes of use. Leave the blower on just turn the compressor off (snow flake button).

You will need the use of a scan tool that is capable of reading the evaporator sensor data. I am not sure about you vehicle but some vehicles have that listed in the engine computer data while others only list it in the HVAC data.

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