AC turns on when I switch to defrost, even though the dial is at max heat.

jay_fyp

Veteran Member
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Oct 29, 2004
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New Jersey
TDI
2015 Golf TDI 6MT 2004 Jetta TDI (PD) 5mt R.I.P - 2013 Golf TDI 6mt - 2004 Golf TDI (PD) 5MT
Anyone have this issue? It's in the 30s here now so naturally I have the dial set on heat. If I go to switch it from any of the directions onto defrost (front window defrost) it switches the AC on, indicated by the AC light. Annoying at most, I really don't want to take it to the dealer but I may have too.
 

40X40

Experienced
Joined
Feb 12, 2006
Location
Kansas City area, MO
TDI
2013 Passat SEL Premium
VW did not do this in the past, but they have apparently changed their approach to combating humidity in the cabin.

The AC removes humidity....

Bill
 

MontrealTDI

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May 10, 2013
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Montreal
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2013 Golf Wagon TDI w/DSG
It is completely normal that the AC switches on when you select the defrost setting. AC dehumidifies the air so it helps clear your windows from fog. Once the windows are clear, you can switch off the AC. Operating as designed.
 

jay_fyp

Veteran Member
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2015 Golf TDI 6MT 2004 Jetta TDI (PD) 5mt R.I.P - 2013 Golf TDI 6mt - 2004 Golf TDI (PD) 5MT
VW did not do this in the past, but they have apparently changed their approach to combating humidity in the cabin.

The AC removes humidity....

Bill
It is completely normal that the AC switches on when you select the defrost setting. AC dehumidifies the air so it helps clear your windows from fog. Once the windows are clear, you can switch off the AC. Operating as designed.
Awesome, did not know this was a "feature". I always knew the defrost with AC on helped defrost windows quicker but never new VW designed it into an actual function on these models. Thanks for the quick responses. Learned something new and glad I don't have to get anything fixed.
 

Diesl

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Dec 3, 2012
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Chicago
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'78 Golf Diesel (long gone); 2012 Jetta Sportwagen TDI w/ DSG
Can I turn AC off and still get the electric heater? Does the vent selection knob have to be all the way set to defrost (12 o'clock)? Does it only come on with the temperature knob all the way up?
And is there really an electric heater?
 

Cooper

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MA
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2011 JSW (traded in 5/2015)
It's just with the knob all the way on defrost. It can be turned off, if desired. It really is needed, though. May get fogging without defrost on.
 

kalobg

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Location
Salt Lake City, UT
TDI
2013 JSW
My '06 Passat always turned on the AC with defrost. This feature probably varies with the level of electronics for the ECEM. I've had cars where you cannot disable the AC with the HVAC set to defrost so it's a nice "feature" on our cars. As has been said before, it is the optimal way to defog the windshield.

If the car is warm with the heat set to 100% and turn on the AC, do you notice a real change? The temperature is about the same to my hand thermometer. The same situation happens with the defrost--the heat temperature is about the same as it would be without the AC, but the AC is condensing the moisture from the air to stop the window from fogging.
 

darkscout

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May 28, 2006
Location
Michigan
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2003 Golf
I'm pretty sure my Mk2 did it as does my Mk3.

I'm not sure how the Mk6 dials are but on my Mk3 I'll crank it all the way to defrost and then set it back 1 tick. So it's 95% defrost but it's enough to turn off the AC.

Keep in mind it's also a good idea to keep everything in the AC system flowing year round. Kind of like how they turn on generators once a week just to make sure they still work. It gets the parts lubed and circulated around.
 

tom28

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Sep 19, 2013
Location
Charlotte, NC
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2011 Golf
VW did not do this in the past, but they have apparently changed their approach to combating humidity in the cabin.

The AC removes humidity....

Bill
This happened in my 2000 Jetta GLX.

And, even better, it blew cool air out the front vents. Which was awesome. I hate my face getting hot.
 

disco biscuit

Well-known member
Joined
Dec 25, 2012
Location
Texas
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2010 Jetta TDI DSG
Almost all vehicles made do this now. This is the first one I came across that let's you turn it off.
 

03_01_TDI

Banned
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Dec 10, 2003
Location
Denmark
TDI
Na
My 07 civic did it as well. But you could program it to not be automatic. I like full control and turned it off. If I want the AC compressor to kick in I will push the button.

Hopefully vagcom can turn this setting off from auto on.
 

VeeDubTDI

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Can I turn AC off and still get the electric heater? Does the vent selection knob have to be all the way set to defrost (12 o'clock)? Does it only come on with the temperature knob all the way up?
And is there really an electric heater?
Yes, there is an electric heater (1,000 watts) and it is completely independent of the air conditioning.
 

vanbcguy

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Feb 22, 2013
Location
Vancouver, BC
TDI
'93 Passat - AHU mTDI with GTB1756VK
I remember the manual for my 1980 Dodge full size van mentioning this very feature. Definitely something auto makers have been doing for a while.
 

tom28

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Location
Charlotte, NC
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2011 Golf
Yes, there is an electric heater (1,000 watts) and it is completely independent of the air conditioning.
How do you get this 1,000 watt heater on? I had dang near no heat this morning going to work. And worse, I got stuck in traffic and the engine actually started cooling off (dropped from its normal 190 degree position). It didn't recover until quite some time after I started moving again.

My toes finally defrosted about an hour after I got to work.

And it wasn't that cold. About 28.
 

Cogen Man

Veteran Member
Joined
Jun 4, 2011
Location
Kingston, Ontario, Canada
TDI
2011 Golf TDI DSG.
How do you get this 1,000 watt heater on? I had dang near no heat this morning going to work. And worse, I got stuck in traffic and the engine actually started cooling off (dropped from its normal 190 degree position). It didn't recover until quite some time after I started moving again.

My toes finally defrosted about an hour after I got to work.

And it wasn't that cold. About 28.
Turn temperature setting to full heat and blower speed to 2 or more. If you have good hearing you may even hear the 1000 watt heater click on. In the winter at a stop light a diesel will drop in coolant temperature. The nature of the beast. My 2011 Golf will show 190*F at the beginning of the stop light and after about 3 minutes waiting for the green my Scangauge II drops to about 175*F give or take. The cluster temp gauge doesn't drop at all because of the buffer they build into it.
 

VeeDubTDI

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If you have Climatronic, it will activate the electric heater automatically.
 

tom28

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Sep 19, 2013
Location
Charlotte, NC
TDI
2011 Golf
Turn temperature setting to full heat and blower speed to 2 or more. If you have good hearing you may even hear the 1000 watt heater click on. In the winter at a stop light a diesel will drop in coolant temperature. The nature of the beast. My 2011 Golf will show 190*F at the beginning of the stop light and after about 3 minutes waiting for the green my Scangauge II drops to about 175*F give or take. The cluster temp gauge doesn't drop at all because of the buffer they build into it.

Yeah.... I did this yesterday. There was no heat. :(

While I was sitting in traffic the temp gauge dropped to almost half way between 0 and 190 degrees. After about a mile of constant moving, it had returned to normal.

I don't have climatronic.
 

Tweak3D

Veteran Member
Joined
May 19, 2010
Location
Graham, WA
TDI
2010 JSW
Yeah.... I did this yesterday. There was no heat. :(

While I was sitting in traffic the temp gauge dropped to almost half way between 0 and 190 degrees. After about a mile of constant moving, it had returned to normal.

I don't have climatronic.
I think it should also be noted that the electric heater will not come on at idle or just above idle, so you typically have to keep moving or it won't work. Also, if its cold enough that you are losing engine temp, you may want to look into a radiator block to use during the late fall and winter months. Will help with heating issues as well as give better fuel economy by keeping the engine warm.
 

nexus665

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Nov 14, 2012
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Austria
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Golf 4 1.9 ALH MY2002
May also be a faulty thermostat - the needle should never drop back in normal usage, not even when you idle for a while after it has warmed up! The gauge needle only drops back when your coolant is pretty far below normal already - it's got a very large area where it'll say "190°F" or "90°C" (over here in Euroland), even though it's from 76°C to 112°C that it shows 90°C in my case.

Regards
 

Windex

Top Post Dawg
Joined
Apr 1, 2006
Location
Cambridge
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05 B5V 01E FRF
Important to note that regardless of if the car automatically turns on the AC to dehumidify the air (as above, this is normal operation in many cars), to leave the RECIRC OFF. if recirc is used in an effort to keep heat in the cabin, humidity will stay in the cabin and fog up the windows.

Defrost = RECIRC off.
 

Cogen Man

Veteran Member
Joined
Jun 4, 2011
Location
Kingston, Ontario, Canada
TDI
2011 Golf TDI DSG.
I think it should also be noted that the electric heater will not come on at idle or just above idle, so you typically have to keep moving or it won't work. Also, if its cold enough that you are losing engine temp, you may want to look into a radiator block to use during the late fall and winter months. Will help with heating issues as well as give better fuel economy by keeping the engine warm.
My auxiliary electric dash heater works at idle ? Not really hot but warm air. It's one of the things I love about this diesel in the cold winter months. Also the seat heater. Toasty buns. :D
The rad or grill block is also a good suggestion. I've used the 1/2" foam pipe insulation. This year I'm going to try some acid flange cover wraps we use at work on acid piping flanges. They measure about 4"X20". Two side by side will cover the lower grill on a 2011 Golf. They have nice acid resistance tie ropes to secure them.
 

VeeDubTDI

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I think it should also be noted that the electric heater will not come on at idle or just above idle, so you typically have to keep moving or it won't work.
Mine does, but it's a Passat with Climatronic so it may behave differently.
 

tom28

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Joined
Sep 19, 2013
Location
Charlotte, NC
TDI
2011 Golf
May also be a faulty thermostat - the needle should never drop back in normal usage, not even when you idle for a while after it has warmed up! The gauge needle only drops back when your coolant is pretty far below normal already - it's got a very large area where it'll say "190°F" or "90°C" (over here in Euroland), even though it's from 76°C to 112°C that it shows 90°C in my case.

Regards
Well, to be clear - it was 22 degrees, F. And I did have heat once the engine came up to temp. It was the first cold day that I'd ever driven the car. Normally it stays on 190 and never moves.

I have a ride-along tomorrow with a VW tech about my radio issues. So, I'll bring it up to him.

May just have to buy electric boots or drive the Outback on crazy cold days. The OB has heat on the engine by the time I get out of my neighborhood.
 

Tweak3D

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Joined
May 19, 2010
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Graham, WA
TDI
2010 JSW
Mine does, but it's a Passat with Climatronic so it may behave differently.
hmm interesting. I don't recall the exact rpm, but I believe its 1200 or so and it was suppose to prevent heavy load on the alternator at idle. I can tell in mine that when its cold you get no clicking from the relay until you start moving. As soon as the RPM's drop under 1200 (pending temp isn't high enough yet) you hear it click off and stay off until the RPM's move back up.
 

tom28

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TDiSkater

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Apr 10, 2011
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Northern Suburbs Chicago
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2011 JSW DSG Salsa Red
This thread kind of reminds me of my wife and her problems with winter AC use. She sees my AC light on my car now and starts yelling at me that it's cold and should be off.

I explained that all cars turn AC on to defrost windows in the winter, under certain conditions. She looks me in the eye and says AC is for cooling in the summer PERIOD. Then calls my car a name. This is not an argument I can win, but at least she doesn't touch the controls anymore.
 

VeeDubTDI

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hmm interesting. I don't recall the exact rpm, but I believe its 1200 or so and it was suppose to prevent heavy load on the alternator at idle. I can tell in mine that when its cold you get no clicking from the relay until you start moving. As soon as the RPM's drop under 1200 (pending temp isn't high enough yet) you hear it click off and stay off until the RPM's move back up.
That's an interesting observation. How many amps is your alternator? The Passat's alternator is 180 amps and the electric heater triggers a fast idle mode (you can view this HVAC fast idle command in VCDS), which is around 950 RPM instead of the normal 800 RPM (plus or minus).
 

Cogen Man

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