My 2014 Mazda 5 blows warm vent air when set to the coldest vent setting with the a/c turned off. I was able to get to the hot/cold air mix actuator thinking I had a malfunctioning unit which prevents the door from closing completely but it functioned correctly when I tested it. I even manually closed the vent door completely and there is still warm to hot air so there seems to be a leak in the door which allows warm air to bleed into the vent when cold air is set at max (without the a/c). When the a/c is on, there is no cold air. Has anyone else experienced this? Any solutions besides pulling the dash and removing the HVAC unit?

Now for the proposed solution. The heater hose is easily accessible under the hood so my thought is to cut the hose and add a shut-off valve to prevent coolant from entering the heater core during the summer months. I know this is a redneck solution but I believe it would take care of the problem as I believe the a/c would function better without the heat bleeding in as well. If I periodically open the valve to ensure coolant flows through to keep the heater core flushed, would there be any other potential problems to other cooling components such as the water pump?

 

I have encountered the exact same problem with my 2014 Mazda5 as well and have been searching for a solution with no success. I was considering doing the same as you suggest regarding the shut off valve through the hose. I cannot see any reason why it would promote blockage in the heater core as long as you open the valve occasionally. I will likely try your suggested solution and will let you know if I have success. I am tired of hot air bleeding in when the actuator is not at fault.

 

Welcome to the forum

I would not really advise the valve because your complete HVAC and cooling system are all designed to work together.
What you are describing is still seems door actuator related?
Cutting off the flow as design may not cause any problems but this goes without saying you should factor in the age of your coolant and when the last complete cooling system flush and replacement was done before restricting or cutting off any coolant flow in the system.

I would like to know that actual temperatures you register in the vent area's of the different setting ? A hand held Digital Thermal meter is great for that. Or if you don't have one or want to invest in a very useful tool a kitchen temperature gauge works great. Not hyper accurate but close enough.

I actually paint pone of them and use it always in my top vents in many of my vehicles. Also a couple of places in the engine compartment.

 

Greetings. Thanks for taking the time to respond and I understand your concerns related to the HVAC functioning if a valve was installed. I will check the temp as you suggest and reply once able. I can confirm that the air is hot and is well over 100 degrees F when the A/C is turned off and automatic function is disabled. I concluded it was the cycling of the HVAC system with the automatic function but then realized that the A/C should not have to work that hard. Also, I confirmed that the heater door actuator is not malfunctioning as I originally though that was the issue and had planned to replace. I will be in touch once I have the temp readings. Thank you again for your time.

 

Thinking about your responses leads me back to the HVAC control as it is all one unit . Are you 100% sure that the mechanical vent doors are closing correctly? And that the heater control valve matches the dash setting of heat off?
Not sure what you mean by the AC is working to hard? If you are on recirculation it is going to draw the cabin cooled air back through the HVAC instead of ram air from the outside which could have the AC cycling more often.
But until you do temperature reading this is guess work. Most us Humans can't really tell degree as they are actually and need a gauge to tell us. We know when things are cold and hot and all the feeling in-between.