Climate control problem

Hi Eric Powers,

Try the following to see if you are able to retrieve any trouble codes.

General troubleshooting information:

How to retrieve a diagnostic trouble codes.

The heater control panel has a self -diagnosis function. To run the self -diagnosis function, do the following:

1 . Turn the ignition switch off.

2 . Turn the fan switch off, the temperature control dial on max cool and the mode control dial on vent.

3 . Turn the ignition switch on (II), then press and hold the re-circulation control switch. Within ten seconds while holding the switch down, press the rear window defogger switch five times. The re-circulation indicator blinks two times, then the self -diagnosis will begin. If there is any problem in the system after self -diagnosis is finished, the re-circulation indicator will blink the diagnostic trouble code (DTC) 7 through 13. When problems in the evaporator temperature sensor circuit are detected (codes 14 and 15), the A/C indicator will blink the DTC. If no DTC's are found, the indicator will not blink.

Canceling the self diagnosis function:

4 . Turn the ignition switch off to cancel the self -diagnosis function. After completing repair work, run the self -diagnosis function again to make sure that there are no other malfunctions.

Max cool position function:

5 . When the mode control dial is in the max A/C position, the heater control panel will automatically select the re-circulation mode and turn the A/C on. The re-circulation switch and A/C switch are disabled and cannot be turned off in this mode. If the control panel fails to function as described, replace it.

Your appreciation is received with thanks.

The system does not use any vacumn lines for dontrols. If the heater and AC does not function as desired, the most likely problem would be the air mix motor. They could be intermittently malfunctioning.

Air max control motor test:

1 . Disconnect the 7P connector from the air mix control motor.

Note: Incorrectly applying power and ground to the air mix control motor will damage it. Follow the instructions carefully.

2 . Connect battery power to the No. 1 terminal of the air mix control motor, and ground the No. 2 terminal; the air mix control motor should run, and stop at Max Hot. If it doesn't, reverse the connections; the air mix control motor should run, and stop at Max Cool.

3 . If the air mix control motor did not run in step 2, remove it, then check the air mix control linkage and door for smooth movement.

"Â If the linkage and door move smoothly, replace the air mix control motor.
"Â If the linkage or door sticks or binds, repair them as needed.
"Â If the air mix control motor runs smoothly, go to step 4.

Fig. 61: Checking Air Mix Control Linkage & Door
Courtesy of AMERICAN HONDA MOTOR CO., INC.

4 . Measure the resistance between the No. 5 and No. 7 terminals. It should be between 4.2 to 7.8 kohm.

5 . Reconnect the air mix control motor 7P connector, then turn the ignition switch ON (II).

6 . Using the backprobe set, measure the voltage between the No. 3 and No. 7 terminals. 6 .

Max Cool-about 1 V
Max Hot- about 4 V

7 . If either the resistance or voltage readings are not as specified, replace the air mix control motor.

To remove the air mix motor, you would have to remove the underdash fuse/relay box.

We need to inspect the temperature sensors that the HVAC system uses to determine duct temperature using a scan tool. When they are failed they actually go to an open circuit. When they do this, they read -40 degree.

I have seen this frequently on newer vehicles that have actual duct temperature sensors on each side. Not so much on older vehicles but the theory is the same. If the sensor is off then when you put the dial to full cold the module moves the actuator to full cold. However, when you move the dial to a warmer position if the temp sensor is open and reading -40, it will start blowing full hot to try to get the temperature up.

If the temperature sensors are not reading incorrectly then it is most likely the control module. However, I would hate for you to replace it without checking the sensors first.

Let me know and we can go from there. Thanks.

The vehicle has an EVAP temperature sensor and it also uses the ambient temperature sensor as you stated.

I am not sure what issue they are going to find inside the unit. Clearly I could be wrong but in my experience it is not inside the unit.

I understand that they searched for codes but they need to hook up the tool and actually read what the sensor is telling the control module. Basically, the control module still gets a valid temperature which is normally -40 when it is an issue, so it will not set a code.

Yes the control module on your vehicle is the panel. Also, to confirm the unit does in fact use the temperature sensors, the EVAP temperature sensor is a direct feed to the module. The unit gets ambient temperature through other modules.

It is true that it effects both but his thinking is off so, it is not true for this issue. If the sensor is reading incorrectly at -40 like I am thinking then why would it blow cold if it already thinks it is -40? The reason it blows cold on full cold is because that is an override to all sensors. When you command max cold with the temperature setting, it just blows as cold as possible regardless of sensor readings.

However, when you begin to move off max cold the temp sensors dictate how it should mix the air to achieve the desired temperature. If the sensor is reading -40 and you want the temp to be around 60 degrees (which is about the commanded temperature on low setting) then the HVAC control module would think it needs to drastically warm up the air to get to that setting which means it would blow max hot. It would do this for all other settings as well because it is trying to get to the temperature setting that you have selected.

Based on what I am hearing, I would recommend taking it to another mechanic as this one sounds like he is guessing or doesn't understand how the system works. In either event, the likeliness that it will get solved is low. If he has a scan tool that can monitor the temperature sensors then this is not difficult to check. If it is telling the HVAC control module the proper temperature then this is not the issue. However, if the HVAC module is reading the temperature as anything that is incorrect then we need to go down this route.