Hi I purchased a new Yeti last May and today for the first time i've felt moved to hit the "Max" defrost windows button due to the low temperatures. The thing is when I do this the AC button also lights up. Surely this isn't right? Also takes a long time for the windows to defrost as the air takes a while to heat up but I guess this is maybe due to the efficiency of the diesel engine right?

Thanks, Mike P.

the ac is on to demist the windows quicker

Hi and welcome,

as gadgetman states the A/C helps take the humidity out the cabin to speed up demist and yes deisels and particularly the Monsters takes for ever to warm up in cold weather, hence on my current Yeti I have the heated screen following my experience with a previous early production 140 SE.

Regards,

TP

All correct and perfectly normal. Also common on lots of other cars.

Hi I purchased a new Yeti last May and today for the first time i've felt moved to hit the "Max" defrost windows button due to the low temperatures. The thing is when I do this the AC button also lights up. Surely this isn't right? Also takes a long time for the windows to defrost as the air takes a while to heat up but I guess this is maybe due to the efficiency of the diesel engine right?

Thanks, Mike P.

Its a Demist not a Defrost button.

Last year I purchased a ceramic heater in Maplins that plugs into the cigarette lighter to help defrost the windscreen. It's not by any means perfect and you won't be blown away (no pun intended) by its efficiency but it's certainly quicker than waiting for the Yeti's heater to clear the windscreen. I mounted it on one of those non slip sat nav dash mats as I didn't fancy drilling holes in my dash.

Hello Mike

The fact that the A/c turning on when you hit the windscreen defroster is proof that the system is working fine .

The A/C system generates heat in a matter of seconds,opposed to the heat generated by a cold engine which will take ages as you know.

Thanks everyone for your replies, all makes sense now. This is a brilliant forum, wish i'd known about it before.

Mike.

The A/C system generates heat in a matter of seconds,opposed to the heat generated by a cold engine which will take ages as you know.

The A/C system does not generate heat.

The A/C system does not generate heat.

Air conditioning is the removal of heat from indoor air for thermal comfort.

In another sense, the term can refer to any form of cooling, heating, ventilation, or disinfection that modifies the condition of air.

An air conditioner (often referred to as AC or air con.) is an appliance, system, or machine designed to change the air temperature and humidity within an area (used for cooling as well as heating depending on the air properties at a given time), typically using a refrigeration cycle but sometimes using evaporation, commonly for comfort cooling in buildings and motor vehicles.

Says Wikipedia.

An a/c unit does generate heat - this is the rejected heat that allows you to have chilled air (compared to ambient); normally this heat is dumped to the atmosphere via the condenser. I am aware of some domestic a/c systems that can run as chillers or heaters, effectively running backwards in heating mode (ie, using the 'rejected' heat and dumping the chilled air). I wasn't aware that automotive a/c systems ran in this mode though. If they did then the dehumidifying aspect would be lost (since the dehumidifying happens as air is chilled, not as it is heated).

None of which has any relevance to the point, which is that the Yeti's A/C light being on does not result in hot air coming out of the demisting vents.

Well, there is relevance if oriki's post is inferred to mean that the waste heat from the a/c is used to heat the cabin air, thus providing almost instant heat compared to the long wait for the coolant to provide any heat through the cabin heater matrix.

I personally don't believe it does, hence you are correct, but that was relevance of the debate.

Many cars activate a/c when max demist is selected and I had always assumed it was for the dehumidifying aspect. I tend to flick the a/c off manually when it does this anyway.

Which is why it is good to have heated windshield.

Or at least I thought so until the temps here hit -15 to -18'C. The heating is not efficient enough in such cold environment (both front and rear heating) - it takes roughly 10 mins to defrost windows. Still better than without it but somehow I expected the heating to be quicker.

Last year I purchased a ceramic heater in Maplins that plugs into the cigarette lighter to help defrost the windscreen. It's not by any means perfect and you won't be blown away (no pun intended) by its efficiency but it's certainly quicker than waiting for the Yeti's heater to clear the windscreen. I mounted it on one of those non slip sat nav dash mats as I didn't fancy drilling holes in my dash.

Is there any risk of heating up the glass too quickly and inducing thermal shock to the glass causing it to crack

I'm thinking of the people who misguidedly pour hot water from a kettle onto the windscreen :S

Is there any risk of heating up the glass too quickly and inducing thermal shock to the glass causing it to crack

I'm thinking of the people who misguidedly pour hot water from a kettle onto the windscreen :S

This shouldn't be an issue with a heated screen as thermal shock damage is caused by sudden differential heating of localised areas of the screen. Because the elements warm the glass up slowly over a large area, there should be no risk. If you pour hot water on the screen, you induce tremendously irregular areas of heat in the glass, and it is this that causes the damage - literally thermal shock.

Edited 3 February, 201214 yr by speedsport

Same goes for the ceramic heater. 100 deg C water onto a -5 deg C screen is rather different to a gentle and gradual warming from a heater.