Strange Heater/AC Operation, v70 1998 Topic is solved

[MrAl]

Hello there,

I found out that i have a strange operation of the heater and AC when the selector control switch is in the 'defrost' position. Very strange, let me try to explain, then explain why this appears to be so strange.

First, when i turn the selector switch to "defrost", the air conditioner comes on. I know this because i see that tiny tiny green light on the AC switch light up rather than the tiny tiny orange light. This happened just this morning when i went out and it was a little cold out so i was turning the heat on and trying to get the defroster to work. I dont think i got it to work right yet, but i had no problem with the windshield after operating the wipers so i was on my way.

Ok, so i get home later, and look in the manual for the v70 1998. What i find is even stranger, and i quote right from the manual:
"When the function selector is in the defrost setting (position), the A/C will automatically be ON if the recirculation is not on and the blower control is not in position 0."

That's the exact quote except for the "(position)" which i added for clarity.

So what exactly does this mean? Does it mean i have to set the blower control to zero (position 0) to get the defroster to work? And does it mean i ALSO have to have "recirculation" on?

EDIT:
I found out that i was reading the wrong section of the manual for the v70, but the RIGHT section says that THE AC WILL BE ON REGARDLESS OF THE SETTING OF THE AC UNIT. WHAAAAAAATTTTTTT ?????????

I mean how crazy is this car? When we turn the defroster on the AC *MIGHT* come on with one model, and with the v70 it comes on all the time in that position, why the heck would they even think that should be necessary in ANY circumstance? Is there some time when we put the defroster on that we want the AC to come on automatically? [Notice: Sarcasm ON] Yeah, when i am driving down the road in the dead of winter and the windshield starts to fog up a little and i turn the defroster on, yeah, i want to make sure it is GOOD and cold in the passenger compartment of the vehicle! HAAA! Thanks Volvo

Thanks for any information on this, and hopefully some explanation why they would make the controls work that way.

[scot850]

The A/C reduces the amount of humidity in the car and so 'de-frosts' the windshield quicker. The A/C temperature is still controlled by the temp settings so no, you are not getting cold air blasted in! That is why the A/C kicks in automatically when de-frost is selected and it works quicker when set to re-circ as it recycles the warm air.

Some cars A/C does not kick in at lower temps. Can't remember is it was a Volvo or not in the dim and distant past, but it said the A/C would not operate below 10C.

Neil.

[abscate]

In these cars the AC evaporator proceeds the heater core. When you select defrost - correct, with Electronic Climate Control, ECC, the AC comes on automatically. The heater core capacity far exceeds the cooling capacity of the AC, so the AC removes the damp from the air, and then the heater brings up the temperature.

Its much faster to defrost with cooler, dryer air than with warmer moist air - which is why this is done.

the A/C will automatically be ON if the recirculation is not on and the blower control is not in position 0."

Lets go Boolean on this one.

AC comes on as soon you select DEFROST unless either of the following conditions are met.



Recirculation is ON (meaning stale air in car)

or

Blower is OFF (fan speed 0)

[BEJinFbk]

An obscurred windshield is the result of cold glass and condensed moisture.
A/C removes moisture. All modern climate control systems engage the A/C
in defrost mode in most conditions.

[sleddriver]

You can defrost w/o engaging the A/C by turning the air control knob one position to the right of "high noon".

[abscate]

One thing I dont know is if defrost mode overrides the no-AC under 0 Centrigrade condition ?

It might be below freezing air is dry enough to defrost without AC

[MrAl]

Hi again,

Thanks for the replies with the explanations. That does help understand this however i still have to wonder a little.

I had cars for years where the AC never came on when i used the heater/defroster, and the windows cleared pretty darn well. Never had a problem with that. But if the AC helps that is interesting, however i can actually feel cold air coming out of the vent. In winter time i dont want that. Still, i will try turning the recirculation on and see if that helps, and also try that 'one position to the right of high noon".

Also, using the AC like that will use more gas right?
Is there no way to defeat that AC coming one, or does turning on 'recirculation' make the AC turn off?
Or does that "one position to the right of high noon" actually turn the AC off and still allow defrosting?

Oh yeah BTW, the cutout is 32 degrees F, where the AC wont come on in any position, at least according to the manual anyway. Earlier today it was maybe 50 degrees F outside, so no where near 32 deg F, but it was still cold in the car without the heater on.

Thanks again.
Maybe the guy who designed the defroster thought that "defrost" translated into "the frost' and so he thinks it should add frost to the windshield "de plane, de plane"

[BEJinFbk]

One thing I dont know is if defrost mode overrides the no-AC under 0 Centrigrade condition ?

It might be below freezing air is dry enough to defrost without AC

I don't generally use the defrost mode, but I can state that I just made
a run at 21 F and the A/C came on when I activated defrost. No sign of
cold air, just the fan going to full speed, the green A/C light coming on
and a lot of hot air being directed at the windshield.

[abscate]

Another mystery solved by Alaskans! Thanks BEJ!

The OCD are free to write to Volvo and tell them their manuals should state this exception.

Al..when cars went electronic this mode (AC with defrost) pretty much became the norm. Using the 12 o'clock plus one notch will defeat the AC enable, though on a P80. On a later P2 defrost is a button which makes defeating it harder.

AC on defrost is perfect for this fall weather when dip down to 0C in the morning and have moisture inside the window.

Compared to the lousy gas mileage you are getting on warmup, the extra AC gas on defrost is a drop if water under the Brooklun bridge, one more car on the Fort Lee bridge, one more fan at a Springsteen concert.

[MrAl]

Hi,

Ok thanks for the new replies. Next time i go out there i'll try to get it working in a way that seems ok for winter and maybe i'll even bring a temperature probe out there to see what kind of temps i am getting and where i am getting them.

One other thing i notice is the defroster air flow doesnt seem all that 'strong'. I can feel a little air but it doesnt seem like it is as much as it should be for such a large windshield. I'm pretty sure the little Hyundai i had had a stronger air flow for the defroster. I'll double check that too though.

Very interesting how cars have changed over the years. For the next future addition i guess there will be a big hammer that comes out and hits you over the head while you are driving so you dont feel the cold as much and your head feels so good when you get out of the car