It's mid July.
The teprature out here in the desert has been swelling at daily average of 98°+.
Question:
Why is there a contsant flow of hot, 85° air eminating from my foot well all day long - even after the temps have dropped down into the 70s' late in the evening.
Please don't tell me it's a clogged heater core (or something like that):(

I have a pre-facelift 04 R53 w/auto air.
I've also have had a Fault code: *08 "HKA: Fan - Inside Temperature Sensor" for sometime now.
No complaints here/from me during the winter months - but....

Any ideas what would be the cause for this hot air blowing from the foot well?

 

From what I have seen when I disassembled the heaterbox there is nothing physical like a valve that stops hot coolant flowing into the heatercore. There is a flap that manages the airflow passing both the heatercore and the evaporator. So basically the heatercore is always hot and the evaporator is always cold, it's on or off, nothing in between. These two airflows are then mixed by the amount of "open" by that flap.

Since you have the auto ac I assume that flap, unlike the manual, is controlled by a little motor which in turn is controlled by the air temp sensor behind the radio/ ac panel. This is guess work as I am no electrician.

If this is the case three things could go at fault: the flap isn't working probably, the temp sensor is bad or your ac needs a refill. Number 2 seems the most likely as you have a fault pointing to it.

 

Another thing to do is move your controls, with some systems the electrical contacts loose connectivity, but when you move them back and forth it allows the connection to reset and the function to work.

Motor On!

 

i'm assuming you have the auto hvac?

there are two temp sensors on the control panel. one on left, one on right. they look like small vents. Those read temp in the cabin. The temps in the cabin effect how the system runs / sets.

you can run a diagnostic on the control panel. it will give you fault codes. I can dig it up for you if you'd like to try that

the mixing flap controls the temp of the air, as LukasH mentioned.

if your flap does not close off the "hot path" all the way you will feel hot / hotter air.

are you feeling that hot air through the front facing vents also?

 

Thanks guys.
All points made seem valid.
@LukasH - Yes. I can definitely admit on 2wo points:
1_I hardly if ever in the past 21 years have I used my AC. And I've lived in the Southern regions of thpe US, where it's hot most of the year. Point being, as I've been told, "not running the AC once in a while is bad for the AC components" (?) - Therefore - I can tell that my refrigerant is low. = my AC blows cool/cold but not artic cold.
2_Yeah. I really should finally replace that inside temp sensor. It's been about a year or so ago since that fault popped up.
@JABowders , Yes. I agree. Even though I have the HKA ; I have also noticed that if I adjust the temp and adjust to certain controls that my AC seems to respond better at producing colder air. Perhaps even quelling some of the hot air eminating from the foot well (?).

 

​​​​@ssoliman - I must have missed your reply.
Very good points/info as well!
Yes. When I first start the car, If the ambient is above 70° or so, warm/hot air does blow from the upper vents for a minute+ . If I toggle the recirculation on and off, cooler but not super cold air eventually comes out. Usually if I haven't been running the AC while driving and then turn it on, it will also blast hot air from the upper vents. Aside from the interior temp sensor needing replacement I'm pretty sure the refrigerant could use a boost.
The lower kick panel by the gas pedal at the bottom of the center console is very warm/hot to the touch as well.

 

+1 on Checking the refrigerant. I'm also thinking the little actuator that opens and closes the "flap" may not be working, you might be able to get your head down there and look up the outlet with a flashlight to see if it is functioning when you press the button for floor air.

Additionally ... on the other side of the firewall you have the exhaust manifold so (in the engine compartment) take a look in and around the back of the engine (exhaust side) that there isn't anything there to restrict air flow. (I have a 1975 MG Midget, and I have the heater totally isolated and after about 2 hours of driving the engine heat builds up and starts to cook my right foot and leg because of lack of airflow)

Motor On!

 

yes sir. sounds like it might be two separate items.

one fix the ac charge / system pressures (low and high).

two make sure the air mix flap is doing its job.

the are three "flaps". one for recirculation or fresh air. one for temp (directs air to heater core or evap), and one for vents (top, bottom, mid). your temp flap is suspect. But i'd start with system pressures

 

here is thread were i had a similar issue. see post #11 and #12 for the control panel diagnostic

https://www.northamericanmotoring.co...t-working.html

 

Awesome! Thanks for the link to the discussion.

Ok - so I didn't dare perform the diagnostic on the main control panel since I'd remembered reading a thread about some not being able to clear the screen/get out of diagnostic mode which was a nightmare for them.

Anyway -:being as unmotivated by the 100° temps to go cramming my head in the footwell - I'd remembered that my Foxwell 510 Elite came equipped with the active test mode for checking/activating the HKA/AC doors and flaps. Happy to say that all including the footwell door functioned perfectly, opening an closing properly
*I will eventually have to pull the trigger ($140) or a new inside temp sensor (hopefully I can find one cheaper) and a full AC evac and recharge (haven't used AC in a long time).
*The couple of times that I tried to pull a used interior temp sensor from a salvage yard 04 & 05 - They appeared to be different than the original one that I currently have in my pre-facelift 04.

 

Fyi this is totally normal as the pipes to the heatermatrix are right behind them.

 

*normal* - Thank you for that!
I was hoping there wasn't something wrong or a more involved repair.

 

Also, if I'm not mistaken there are foam seals around the heater core to prevent hot air leaking where it shouldn't. May be worth a look, not hard to get the heater core out and new cores come with new seals iirc.

 

My advice; if it ain't broken don't fix it.

After replacing my evaporator, which involves taking the heatermatrix out, the heatermatrix was leaking. The rubber seals are quite hard to sit right and the clamps are impossible todo with just two hands.
I had to replace those seals by purchasing kit 64116910914, which also come with a new air seal for the heatermatrix.

Part #3

 

Check with AllMagautoparts out of Florida for the “inside temp sensor” …

 

Allmag = +1
Just about the only search that matches what I currently have installed in my HKA. 'Would prefer new but. Preowned @$39 from a used parts site I trust.