A/C blowing on and off

Welcome to 2CarPros.

I need to better understand what is happening. Do you mean you adjust for the AC and it works but the heat comes on and the system goes back and forth? Also, does it do it on both sides of the truck? Last, do you have automatic temperature control or manual?

Let me know.

Joe

It's automatic climate control. Heat or cold or at any speed the fan blows on and off. It blows hard and then very soft. I can see the A/C clutch turning on and off. Not sure if it's just low on Freon, the clutch or the sensor is bad.

Welcome back:

The AC clutch is supposed to cycle, so that sounds normal. Since the fan keeps changing from blowing hard to soft, I have a feeling the HVAC control module is acting up for you. However, even a bad blower motor can do this.

The HVAC control module performs the following functions to maintain the desired air temperature:
- Monitor the following sensors:
- Inside Air Temperature Sensor
- Ambient Air Temperature Sensor
- Lower Left Air Temperature Sensor
- Lower Right Air Temperature Sensor
- Upper Left Air Temperature Sensor
- Upper Right Air Temperature Sensor
- Regulate blower motor speed
- Position the air temperature actuator
- Position the mode actuator
- Position the recirculation actuator
- Request A/C operation

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See pic 1 for HVAC control module.
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Now, if the selected temps remain consistent, it may be the blower motor control processor. Here are directions related to its replacement.

HVAC SYSTEMS - AUTOMATIC
BLOWER MOTOR CONTROL PROCESSOR REPLACEMENT

REMOVAL PROCEDURE


pic 2

1. If equipped, remove the sound insulator panel.
2. Disconnect the electrical connector at the blower motor.


pic 3

3. Disconnect the electrical connector (4) from the blower motor control processor (2).
4. Remove the blower motor control processor retaining screws (3) from the HVAC module (1).
5. Remove the blower motor control processor (2) from the HVAC module (1).

INSTALLATION PROCEDURE

pic 4

1. Install the blower motor control processor (2) to the HVAC module (1).
2. Install the blower motor control processor retaining screws.

Tighten the screws to 1.6 N.m (14 lb in).

NOTE: Refer to Fastener Notice in Service Precautions.

3. Connect the electrical connector (4) to the blower motor control processor (2).


pic 5

4. Connect the electrical connector at the blower motor.
5. If equipped, install the sound insulator panel.

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Now, since I made this extremely confusing, and I'm sorry for that, here is what I suggest. If the module, processor, or one of the HVAC temp sensors is failing, there will be a diagnostic trouble code stored in the system. This will not be typical P type code that any scanner can read, but requires a more sophisticated scanner. I would recommend having the system checked before we just start throwing parts at it. The procedures are not the easiest and parts are not the cheapest. I would hate to tell you to replace a module and be wrong. I hope you understand.

Let me know your thoughts.

Joe

Thank you. I found a place that said they would diagnose it for free.

Great! Let me know what they find and what codes are retrieved. That way I can tell you if what they say makes sense.

Take care,
Joe