Exploring the HVAC system in detail (with videos)

[nick88highline]

Now the fourth part in which I go through, in detail, the flow of air through the HVAC box:


View: https://www.youtube.com/watch?v=sJv4m1fw900


This might help to explain some issues, but if not, let me know and I'll focus on those.

 

[Green]

Nick, thank you for your videos!
I asked you this question on YouTube on your Part 3 video as well...Do you find that the pump/actuator functions differently in Auto versus Manual mode? I have the situation where the pump seems to remain open, even in LOW setting, and the air coming out of the rear is as hot as the sun. Are there any sequence of settings that get the actuator to force closure? Any information would be appreciated. Thank you again! Cheers

 

[ADVAW8S]

Now the fourth part in which I go through, in detail, the flow of air through the HVAC box:


View: https://www.youtube.com/watch?v=sJv4m1fw900


This might help to explain some issues, but if not, let me know and I'll focus on those.

Thank you for this, it explains a lot. I will add an observation based on your teaching. I think the reason why the rear gets no heat when on foot, is because the vent for feet blows air to slant portion of driver and passenger footwell. The slant then pushes the air towards the rear passenger. While defrost goes up the window and then heads to back. The other thing I will mention, is I assume the cool open air that does not go over the hot water, is the mixing air. We have the ability to set a temp. I assume the cool air mixes with the hot air and the hot air flap dictates how much hot air is passed into the mixing chamber.

Finally, the missing piece to cabin temp management is the vent closure. I tend to run my cabin on defrost and foot. Then I close the middle vent flaps to eliminate the cool air that gets push to direct face. The side circle vents provide warm air, again pushed to back. In the summer, on real hot days, I run just face and open the side vents. The defrost creates condensation on the front window. I also never have my fan above 2. It's 1 or 2 which I think does a better job of moderating the cabin temp.

 

[Blackwolf]

Thanks Nick, very interesting.

 

[Shopkeep]

Awesome work, bonus points for the Harry Potter wandage.

 

[255/85]

The one problem I can see are all the plastic connections. The shaft splines that the actuators engage with do seem fairly stout but some could have stripped already especially if - as @Badger_4x4 mentioned previously - one or more actuators and/or valve flaps were not zero'd correctly at assembly. You might not be getting flap movement despite seeing actuator rotation. If that's the case then it's full disassembly. Probably cheaper to replace a few actuators with the ones off your spare. Maybe drill a few small holes for your camera at some point too.

The drawings are just fine by the way.

 

[Happyoldgit]

I think I get the gist now. Excellent explanation Nick thank you.

 

[nick88highline]

Nick, thank you for your videos!
I asked you this question on YouTube on your Part 3 video as well...Do you find that the pump/actuator functions differently in Auto versus Manual mode? I have the situation where the pump seems to remain open, even in LOW setting, and the air coming out of the rear is as hot as the sun. Are there any sequence of settings that get the actuator to force closure? Any information would be appreciated. Thank you again! Cheers

My Auto mode does not work (light does not come on), so I don't know how they function differently. I can see the heater valve actuator and that moves around 90 degrees which is what you would expect to open and close it. It does seem that at some point the heater valve is opened and then never closes, which in my opinion, overheats the unit as you would never want coolant temperature air blasted at your face. I've tried all sorts of combinations of controls, startup sequences, resetting the HVAC unit, but it remains the same. I think my HVAC control unit is probably faulty.

 

[Blackwolf]

Are the actuators keyed or indexed to the flap operating shafts in any way? If not I guess they'd have to determine the limits of flap movement and self-calibrate on each boot-up. It occurred to me that if the ECU lost its knowledge of the flap position it might explain some of the odd behaviours.

 

[Industrifoto]

I believe they perform a full movement to calibrate every time you change the settings. Hence, the blasts of warm or cold air through the vents even for minor changes.

Are the actuators keyed or indexed to the flap operating shafts in any way? If not I guess they'd have to determine the limits of flap movement and self-calibrate on each boot-up. It occurred to me that if the ECU lost its knowledge of the flap position it might explain some of the odd behaviours.

 

[CRH]

My Auto mode does not work (light does not come on), so I don't know how they function differently. I can see the heater valve actuator and that moves around 90 degrees which is what you would expect to open and close it. It does seem that at some point the heater valve is opened and then never closes, which in my opinion, overheats the unit as you would never want coolant temperature air blasted at your face. I've tried all sorts of combinations of controls, startup sequences, resetting the HVAC unit, but it remains the same. I think my HVAC control unit is probably faulty.

Can you not get it to a dealer to have it fixed, it's obviously faulty.
Contact IA directly if you are getting nowhere with your dealer

 

[255/85]

Are the actuators keyed or indexed to the flap operating shafts in any way? If not I guess they'd have to determine the limits of flap movement and self-calibrate on each boot-up. It occurred to me that if the ECU lost its knowledge of the flap position it might explain some of the odd behaviours.

They are usually keyed together. You can see the male star-shaped keyway on the heater valve and on the corresponding actuator at 3:50 in the first video. Post #8 links to a couple of BMW actuators that also evidence the female keyways.

In my limited experience I've encountered both types of calibration - factory set and continuous. The ones that continue to recalibrate ad infinitum can cause breakage over time as doors/flaps max out their range of movement (and spike resistance values?) eventually stressing the weakest link in the mechanisn. There are several US companies making repair kits for some of the most problematic vehicles substituting metal for OE plastic components.

 

[Skydance]

My Auto mode does not work (light does not come on), so I don't know how they function differently. I can see the heater valve actuator and that moves around 90 degrees which is what you would expect to open and close it. It does seem that at some point the heater valve is opened and then never closes, which in my opinion, overheats the unit as you would never want coolant temperature air blasted at your face. I've tried all sorts of combinations of controls, startup sequences, resetting the HVAC unit, but it remains the same. I think my HVAC control unit is probably faulty.

Some manufacturers when the auto climate control doesn’t work. You can press a combination of buttons to recalibrate the system. Might to worth a try but taking it to your nearest dealer is the best bet.

 

[nick88highline]

Can you not get it to a dealer to have it fixed, it's obviously faulty.
Contact IA directly if you are getting nowhere with your dealer

Yes, that is what a sensible person would do. Trouble is that at this stage I'm not sure what the "fix" would end up being. Until I'm certain that a revised control unit works then I'll probably hold off. Also, what I failed to mention was that 1% of the time, the AUTO works and the light comes on, so you can guess what would happen at the dealership...

They are usually keyed together. You can see the male star-shaped keyway on the heater valve and on the corresponding actuator at 3:50 in the first video. Post #8 links to a couple of BMW actuators that also evidence the female keyways.

In my limited experience I've encountered both types of calibration - factory set and continuous. The ones that continue to recalibrate ad infinitum can cause breakage over time as doors/flaps max out their range of movement (and spike resistance values?) eventually stressing the weakest link in the mechanisn. There are several US companies making repair kits for some of the most problematic vehicles substituting metal for OE plastic components.

The actuators must be self-calibrating otherwise assembly would be a nightmare, at least in my opinion. I will do a video on the wiring and actuators shortly. Looking inside the actuators is like looking into a fine Swiss watch, except that all the hundreds of cogs are plastic.
I also have a Jeep Grand Cherokee WJ V8 which is infamous for its HVAC flaps which become loose on the shafts resulting in somewhat poor performance.

What I have noticed is that if I don't touch the controls and leave everything "off", ie all controls to the left, the heater coolant valve does not open. As soon as I turn the fan on (without touching anything else and the temp being max cool) the water valve opens and 90 degree coolant comes through and burns my fingers. The valve does not close. Clearly a control issue...I think,

 

[255/85]

Yes, that is what a sensible person would do. Trouble is that at this stage I'm not sure what the "fix" would end up being. Until I'm certain that a revised control unit works then I'll probably hold off. Also, what I failed to mention was that 1% of the time, the AUTO works and the light comes on, so you can guess what would happen at the dealership...




The actuators must be self-calibrating otherwise assembly would be a nightmare, at least in my opinion. I will do a video on the wiring and actuators shortly. Looking inside the actuators is like looking into a fine Swiss watch, except that all the hundreds of cogs are plastic.
I also have a Jeep Grand Cherokee WJ V8 which is infamous for its HVAC flaps which become loose on the shafts resulting in somewhat poor performance.

What I have noticed is that if I don't touch the controls and leave everything "off", ie all controls to the left, the heater coolant valve does not open. As soon as I turn the fan on (without touching anything else and the temp being max cool) the water valve opens and 90 degree coolant comes through and burns my fingers. The valve does not close. Clearly a control issue...I think,

By "off" I assume you mean with the temp control dial turned all the way to the left - i.e. - cold?

What we don't know is whether or not the heater valve always opens at start-up and cabin temp is then controlled by the blend door. Many vehicles work that way and "blend" varying amounts of cool and heated air rather than varying the amount or rate of coolant that gets pumped through the heater core.

Here's a link to one of the repair kits for WJs through 2004, Scroll through the left menu for your year...

Grand Cherokee Heater Repair