Q: Why is my car blowing hot air and cold air at the same time?

asked by on January 18, 2017

The other day i took out my HVAC system from the car trying to fix the LED screen, which I did not fix. After I but the system back into the car and took it for a drive the air started blowing hot and cold. It would blow hot air from the side vents towards the doors and the floor vents. It would also blow very cold from the center vents.

My car has 66000 miles.
My car has an automatic transmission.

Heater is not working Inspection $94.99 - $114.99 Get a Quote

The answer to this depends on whether you have switched on heating, cooling (A/C) or neither. In one scenario, for example, if you have not switched on the A/C system, but the A/C is running as confirmed by a visual check of the A/C compressor, and you are getting cool air obviously there is an electrical problem. The coincidental heating could be due to a blend door malfunction. If the only thing you did was remove electrical or electronic components, it would appear that you have an electrical malfunction in the controls. I recommend you request an HVAC diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing


Experienced Mechanic?

Earn up to $70/hr

What others are asking

1995 Suzuki Escudo 16-valve won't start unless spraying the fluid in intake
It starts with starting fluid. That means that the ignition system is working, so you most likely have a fuel system problem. What you want to do is pressure test your fuel pump. You can get any mechanic to do...
Break problems
Hi there: Your boyfriend has a serious brake issue that should be repaired immediately. The loud noise is most likely coming from the brake pads (https://www.yourmechanic.com/article/symptoms-of-bad-or-failing-brake-pads) grinding on the brake rotors. When he applies the parking brake, it's only applying...
Truck running hot. Already changed water pump, thermostat, and heater hose. No water in my oil. Still running hot
You will need to have your cooling fan clutch checked for lock up. If the clutch is replaced from lack of lock up when it gets hot then have the radiator (https://www.yourmechanic.com/services/radiator-replacement) checked for coolant flow through all the passages....
Lights and gauges quit working, buzzing noise
Hey there, I would start by testing the fuses. This is a common problem on this generation of Mercedes diesels. There is an OVP relay that sits behind the battery which are also a known source of problems. I would...
I have a loss of power when acceleration the car does not drive pass 10 or 15mph I change the plugs and also change the fuel filte
This may be result of a failing or dirty mass airflow sensor (https://www.yourmechanic.com/services/mass-airflow-sensor-replacement). This is a unit that is responsible for regulating the air flow into the engine as it is mixed with fuel prior to being injected into the...
My car had a rough idle, and if I sit at a red light or let the car run in idle for a few minutes my check engine light starts to
A dead misfire on a single cylinder may be deeper than just a spark plug (https://www.yourmechanic.com/services/spark-plugs-replacement). If the compression for that cylinder is very low, the cylinder cannot fire. Low compression would be caused by worn piston rings. Also, if...
Starter removal
Hello. I would need to know which engine that you have in your truck to know the correct removal process for the changing of this starter. If the engine is not cranking, then it may indeed be the starter, as...
Temp gauge goes up and down while driving 2006 Infiniti G35
Hi there - either the recent cooling system work did not thoroughly bleed all the air out of the system, or you still have a bad thermostat (https://www.yourmechanic.com/article/how-long-does-a-thermostat-last) - even the new one. A properly working thermostat should manage coolant...
Do you need to reprogram after replacing throttle body on 04 trailblazer
The Service Manual does not "require" any specific intervention (re-learn procedure). On this vehicle, the PCM will, by default, update itself to new values, just as you idle and drive the vehicle, if such new values are required. Even if...

Related articles

Ten Sports Cars That Double as Good Daily Drivers
The best daily driver is a car that's reliable, usable, and still fun to drive. Popular daily sports cars include the BMW M3, Subaru WRX, and VW GTI.
What Does the Distance Warning Light Mean?
The distance warning light turns on when your car is in danger of hitting another car or obstructing object.
Top Automotive News & Stories: September 24-September 30
Angry Civic Type R, 350 special edition Ferraris, Infiniti variable compression tech, Mercedes' electric future, and more.