HVAC blows warm under hard acceleration
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Super Member
Joined: Dec 2007
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2005 S500 Designo
HVAC blows warm under hard acceleration
So the HVAC system in my car does two funky things.
1. Under hard acceleration the whole system tends to blow hot/warm air where it previously is running cool.
2. Opening any window or the sunroof while driving causes warm air to blow in the footwell. I believe this happens regardless if the car is set to recirculate.
I fixed the thermistor in the top (welded in some wire). The outside air temperature indicator is accurate.
1. Under hard acceleration the whole system tends to blow hot/warm air where it previously is running cool.
2. Opening any window or the sunroof while driving causes warm air to blow in the footwell. I believe this happens regardless if the car is set to recirculate.
I fixed the thermistor in the top (welded in some wire). The outside air temperature indicator is accurate.
Super Member
Joined: Aug 2005
Posts: 591
Likes: 9
From: Covington, WA
'96 SL600, '05 S55 AMG, '06 C230
Regarding scenario #1, this is not unusual for any vehicle, depending on how long the hard acceleration is occurring. Full-throttle events cause a drop in system vacuum, which can cause AC valves to momentarily disengage. If the outside air is radically different than the cabin air, and the cabin air fan(s) is running at a higher speed, one may sense a momentary change in air temp. I would check the overall AC circuit pressure to reassure myself that the system is fully capable. Otherwise, IMHO, it's the nature of the beast.
Cheers,
Jeff
Cheers,
Jeff
Thread Starter
Super Member
Joined: Dec 2007
Posts: 980
Likes: 224
2005 S500 Designo
Interesting. I figured the car might disengage the compressor, although I wouldn't expect an immediate loss of cooling. Our old Volvo S90 does the same thing, although recently it's gotten much more pronounced.
Any idea on opening a window causing air to blow warm from the lower vents?
Any idea on opening a window causing air to blow warm from the lower vents?
Super Member
Joined: Aug 2005
Posts: 591
Likes: 9
From: Covington, WA
'96 SL600, '05 S55 AMG, '06 C230
Regarding scenario #2, I would suspect, perhaps, a weak AC directional valve. Perhaps with the windows and/or sunroof open, there is a mean-free path for air to be blown through the cowl inlet, through a weak AC valve, into the footwell(s), and out open window. With the windows and sunroof closed, the cabin is allowed to pressurize slightly, thus restricting the amount of 'fresh' (aka warm) air entering the cabin. Look for a broken or loose vacuum line. I had this problem on an old Corvair a bazillions years ago.
Cheers,
Jeff
Cheers,
Jeff
Thread Starter
Super Member
Joined: Dec 2007
Posts: 980
Likes: 224
2005 S500 Designo
Mr. Jeff I suspect something along those lines (free air flow).
Problem is, how do I even begin to start working on this?
If it's too complicated, it's really not a huge problem, and I can let it slide.
Problem is, how do I even begin to start working on this?
If it's too complicated, it's really not a huge problem, and I can let it slide.
