[Shredstone]

I found a post about a year old with this same question, but no real answer. Dual climate controls can sometimes produce really different temps on each side, even with the same settings. Are there sensors in the car trying to measure whether the driver or passenger side needs more heat or cooling?

[IceGoaliePaul]

You turn the knob up one degree and it blasts hot air at you. You turn it down one degree it blasts cold air.

I think it must have some kind of infrared heat sensor as today the ambient temperature was showing as 35F with temperature set to 70F but it was blowing cold air. I think my body temperature was likely warm as I had just played hockey so it decided cooling was needed even though everything else was cold.

I wish they had a climate control app on the infotainment screen so you could tell exactly what was going on and ideally set it to different modes like controlling the outlet temperature or just a heat percent like old dumb car heating systems. Whatever it does now often isn't what I want.

[crosive]

theres a temp sensor by your right knee that reads what is in the car itself (for the driver). I'm unsure where the passenger one is for the dual systems.

you set a temp, the climate control tries to get that sensor to the temp you set. It also has a sensor in the air stream to tell what temp the air is blowing, so it can determine if it needs to change it to match what it needs. There is also an option in the display that lets you change how hard the air will blow on it's lowest setting.


of the 2 camaros I've had, they haven't been off hardly at all. I can set it to 72-74 depending on my mood, and it works fine everytime, even if my wife has her side on 78-79.

however, you can influence that sensor with your own body heat if you are huddled up around it.

[Petrol Head]

There are two sensors, on most cars they’re in similar locations in the lower half of the dashboard usually by the driver/passenger knees.

It works just about the same as the thermostat in your house. In the old days there was a mercury switch and the temperature slide switch was a rheostat. Today they use RTDs (resistance temperature sensors). There’s a damper inside the HVAC vents that adjust and mix the right amount of hot air from the heater core and cold air off the A/C evaporator that will continually adjust based on current readings (ambient cabin temp on driver or passenger side) of the RTD and temp settings for driver and passenger.

Only difference between your home thermostat and the car’s is you have to manually switch from heat to A/C in your home. The car will run the A/C in all conditions unless you override it and turn it off or do not run the climate control in full auto mode.

This is due to the fact that a car is a tightly enclosed environment susceptible to humidity.

[ctrlz]

Originally Posted by Petrol Head

you have to manually switch from heat to A/C in your home...

Live the dream, baby!
Enable auto changeover in the service menu. Most 'stats are capable these days.

[crosive]

Originally Posted by Petrol Head

Only difference between your home thermostat and the car’s is you have to manually switch from heat to A/C in your home.

no I don't. however, there is a 2 degree variability between the heat and cooling.

that won't cut it in the car to me.

if you set it to one temperature and let it heat or cool to it's desire, you'll wear equipment out because of the constant auto switching. you have to have a bit of hysteresis otherwise you'll never get it the way you want it, and neither will it.

[Petrol Head]

Originally Posted by ctrlz

Live the dream, baby!
Enable auto changeover in the service menu. Most 'stats are capable these days.

Yes you’re right there are new smart thermostats that will change over automatically. But they won’t be running the furnace and A/C at the same time.

Your car does.

[Petrol Head]

Originally Posted by crosive

no I don't. however, there is a 2 degree variability between the heat and cooling.

that won't cut it in the car to me.

if you set it to one temperature and let it heat or cool to it's desire, you'll wear equipment out because of the constant auto switching. you have to have a bit of hysteresis otherwise you'll never get it the way you want it, and neither will it.

Not sure what you mean. I have 167,000 miles on my 2009 Accord V6 and I’ve used nothing but auto mode on the climate control at 72 degrees. For 10+ years. I don’t think I’ve even touched the climate buttons other than the front or rear defrost.

[crosive]

Originally Posted by Petrol Head

Not sure what you mean. I have 167,000 miles on my 2009 Accord V6 and I’ve used nothing but auto mode on the climate control at 72 degrees. For 10+ years. I don’t think I’ve even touched the climate buttons other than the front or rear defrost.

I meant if you set the temp to e.g. 72 degrees and it had an auto mode that went from hot to cold, it would be constantly going back and forth fighting itself. You'd have to have a range, e.g. 69 heat and 72 cold so it's not just swapping all the time.

No car does this. No house does this. I mentioned it because if a car did do this, you'd still need the hysteresis of a few degrees, and nobody would be comfortable with that. I wouldn't be.

[ctrlz]

Below is from the repair manual. It doesn't quite work like home HVAC. Cars often keep the A/C running all the time to remove humidity. They just route cooled air across the heater core to rewarm it. There are a lot of sensors in play here. Both left and right side of the cabin have upper and lower duct temp sensors plus there is the center sun load sensor. The A/C has an evap temp sensor and a refrigerant pressure sensor. Those are the basics. All the actuators for the dampers also have position sensors.

DESCRIPTION AND OPERATION > AUTOMATIC HVAC DESCRIPTION AND
OPERATION > HEATING AND A/C OPERATION

The purpose of the heating and A/C system is to provide heated and cooled air to the interior of the
vehicle. The A/C system will also remove humidity from the interior and reduce windshield fogging.
Regardless of the temperature setting, the following can affect the rate that the HVAC system can
achieve the desired temperature:
Recirculation actuator setting
Difference between inside and desired temperature
Blower motor speed setting
Mode setting
When the A/C switch is pressed, the HVAC controls sends a signal to the HVAC control module via
LIN-Bus. The HVAC control module evaluates this signal and sends an A/C request signal to the ECM via
CAN-Bus. The ECM checks all preconditions before releasing and if all conditions are met sends a
release signal back to the HVAC control module. The ECM will provide a ground for the A/C compressor
relay enabling it to close its internal contacts to send battery voltage to the A/C compressor clutch coil.
The A/C compressor clutch will be activated. The performance of the A/C compressor is regulated via a
variable A/C compressor solenoid valve. The HVAC control module supplies battery voltage to the A/C
compressor. When the A/C switch is pressed, the HVAC control module provides a pulse width
modulation (PWM) signal to the A/C compressor solenoid valve in order to command the performance of
the A/C compressor.
The following conditions must be met in order to activate the A/C compressor:
Battery voltage is between 9-18 V
Engine coolant temperature is less than 124°C (255°F)
Engine speed is greater than 600 RPM
Engine speed is less than 5500 RPM
A/C high side pressure is between 269-2929 kPa (39-425 PSI)
Throttle position is less than 100%
Evaporator temperature is greater than 3°C (38°F)
ECM does not detect immoderate torque load
ECM does not detect insufficient idle quality
The ambient temperature is above 1°C (34°F)
The sensor information is used by the ECM to determine the following:
The A/C high side pressure
An A/C system load on the engine
An immoderate A/C high side pressure
The heat load at the A/C condenser
The air streams into the passenger compartment through the heater core and the evaporator core. The
air temperature actuator drives the mixed air door to direct the airflow. If the interior temperature should
be increased, the mixed air door is put into the position in which more air streams through the heater
core. If the interior temperature should be decreased, the mixed air door is put into the position in which
more air streams through the evaporator core.

DESCRIPTION AND OPERATION > AUTOMATIC HVAC DESCRIPTION AND
OPERATION > RECIRCULATION OPERATION

The recirculation switch is integrated into the HVAC control. The selected recirculation switch position is
sent to the HVAC control module via LIN-Bus. The HVAC control module controls the air intake using the
recirculation actuator. In recirculation mode the recirculation door opens in order to circulate the air
within the vehicle. In fresh air mode the recirculation door is closed in order to route outside air into the
vehicle.

DESCRIPTION AND OPERATION > AUTOMATIC HVAC DESCRIPTION AND
OPERATION > AUTOMATIC OPERATION

In automatic operation, the HVAC control module maintains the comfort level inside of the vehicle by
controlling the A/C compressor clutch, the blower motor, the air temperature actuators, mode actuator
and recirculation actuator.
To put the HVAC system in automatic mode, the following is required:
The auto 1. switch must be activated.
The air temperature switch must not be in either the full 2. hot or full cold position.
Once the desired temperature is reached, the blower motor, mode, recirculation and temperature
actuators automatically adjust to maintain the temperature selected. The HVAC control module performs
the following functions to maintain the desired air temperature:
Monitors the following sensors:
Ambient air temperature sensor
Duct air temperature sensors
Ambient light/sunload sensor
Regulate the blower motor speed
Position the air temperature actuators
Position the mode door actuator
Position the recirculation actuator
Request A/C operation
Control of the A/C compressor
When the warmest position is selected in automatic operation the blower speed will increase gradually
until the vehicle reaches normal operating temperature. When normal operating temperature is reached
the blower stays on high speed and the air temperature actuators stays in the full heat position.
When the coldest position is selected in automatic operation the blower stays on high and the air
temperature actuators stay in full cold position. The mode actuator remains in the panel position and the
recirculation actuator will remain in the recirculation position.
Under cold ambient temperatures, the automatic HVAC system provides heat in the most efficient
manner. The operator can select an extreme temperature setting but the system will not warm the vehicle
any faster. Under warm ambient temperatures, the automatic HVAC system also provides air
conditioning in the most efficient manner. Selecting an extreme cool temperature will not cool the vehicle

any faster.

[Need4Camaro]

Question. I've always been told that running the heat with the A/C is bad for your A/C system. Is there any truth to that?

[Petrol Head]

Originally Posted by Need4Camaro

Question. I've always been told that running the heat with the A/C is bad for your A/C system. Is there any truth to that?

Nope. In fact that is how your front defogger works, and has always worked since they started putting air conditioning compressors in cars. When you engage the front defog it engages the A/C compressor, and turning it up hot is actually the most efficient and effective way to remove fog and moisture from inside the car.

In days before rear defrost was standard, if you had air conditioning in the car and turned the defog up and the temp to warm or hot it would defog everything pretty well.

[ctrlz]

Originally Posted by Need4Camaro

Question. I've always been told that running the heat with the A/C is bad for your A/C system. Is there any truth to that?

I don't think so, as this is now pretty commonplace, particularly with higher end auto-climate systems. It just happens behind the scenes. Even my 1990 Accord had a recommendation to (manually) run the A/C with heat in winter to assist in defogging the windows.

[Petrol Head]

Originally Posted by ctrlz

I don't think so, as this is now pretty commonplace, particularly with higher end auto-climate systems. It just happens behind the scenes. Even my 1990 Accord had a recommendation to (manually) run the A/C with heat in winter to assist in defogging the windows.

See my post right above yours