? Does the A/C operate on "defrost" setting to dry the air?

[NewbieBaby]

My past cars/trucks had this heating system logic: when the window defrost is activated, and independent of whether the heat was on or not, the AC system operated in order to pre-dry the air before/after passing over the heating exchanger but before the forced air was blown onto the window. This acted to remove interior window fog almost immediately.

In my A4 Golf, I have the impression that when the duct selection dial is set to blow on the windshield inside (selector at 12:00), that the AC system does not seem to be operating to dry the air before it is blown onto the windshield surface. The performance of my 02 Golf in this regard is that interior fog removal is quite slow compared to other cars I am familiar with. I have consulted the Bentley manual, but no system logic is discussed.

Does anyone know if the VW's AC should be operating to dry the forced heating air while the the defrost setting is selected?

Thank you for your time.

[ October 27, 2002, 11:24: Message edited by: NewbieBaby ]

 

[weedeater]

You have to push in the A/C button.

 

[dieseldorf]

Originally posted by weedeater:
You have to push in the A/C button.

<font size="2" face="Verdana, Helvetica, sans-serif">...assuming the ambient temp is above ~40F, the A/C compressor will run to de-humidify the passenger compartment.

 

[SoTxBill]

on my 96 passat, no, on my 01 jetta yes... the logic is built in..

 

[PackRat]

My A3 doesn't. The only cars I have seen that did run the AC automatically with the defrost were US cars where there was no separate AC button. Like the "old tyme" GM selector "MAX AC, AC, BI-LEV, VENT, HEAT, DEF".

 

[Oo-v-oO]

The A/C in my '98 will not run even if I ask it to if the temperature is too low outside. I thought you were supposed to run the A/C once a month or so at a minimum to help keep the compressor seals lubricated? Not going to happen here in NH! I'm lucky to actually have to use the A/C a few months out of the year.

-Lee

 

[C Brown]

On a simmilar note, I notice on my 97 Jetta, that if you DO turn on the AC, the fans run regardless. This further coolis off your motor, attempting to warm up.
I am currently doing experiments with the normally fitted EGR heat exchanger(TO COOLANT) to vent the heat exchanger exaust to atmo after the turbo, EG (exaust manifold to heat exchanger to vent) with a seperate EGR type valve, to get the benifit of the 170F degree exaust temp at idle. This heat exchanger is directly plumbed into the the heater core. This setup will causes excessive smoke if you leave the EGR output vented to atmo and blip the throttle, due to the lower boost available. I beleive this could help prevent the engine cooling off during in trafic or idle -warm up, if properly controlled to be vented only at idle.

Need to pump the water to the heater core using an electric pump and thru only the EGR heat exchanger, and back to the heater core to get an idea of it's output ablility.

A larger heat exchanger might be better, but any extra heat at idle, can't be a bad thing.

Regards
CB&Stoker

 

[NewbieBaby]

For my question, I think weedeater is correct. In Houston at this time of year(I do not expect to see the colder temperatures and the low temp limit for AC on)the interior window surfaces seem to fog easily. By running the AC (push the button in stupid, is what he probably wanted to say) with the heater on, the window clears up quickly. And for this locale, the cabin temperature seems to controllable to best effect.

Thanks to all for their responses, I think my problem is solved.

 

[TEXAS_TDI]

I'm still using the A/C in my car and in my house.

 

[weedeater]

push the button in stupid, is what he probably wanted to say

<font size="2" face="Verdana, Helvetica, sans-serif">well....

 

[mickey]

'99 New Beetle: I must push the A/C button.

'99 Jeep: A/C runs on defrost.

I prefer to make the decision myself.

-mickey