rear air con again

[marinabrid]

on earlier post i mentioned my rear dual air con not working, have just done a temp test and may be able to shed some light.

outside temp according to dash is 17c      the temp outside is the same with my kitchen thermometer .      the front vent temp with air con on is 6c

i put the thermo in the rear vent and was staggered to see it 24c,  much higher than outside
so   i have read somewhere about sticking flaps or something   and a way of re setting them ?  or is it a motor ?   there are no faults showing on vag com on the module.
a little puzzled i am now !

thanks in advance   

[insanitybeard]

From which of the rear vents did you measure the temperature?

[SilverBeast]

Have you checked the aluminium air con pipes under the floor of the car on the passenger side.  One should be cold and the other hot - I can't remember which.

The rear air-con basically uses T pieces off the front system to take the high pressure liquid refrigerant (probably the thin pipe) to the rear evaporator.  It goes through a thermostatic expansion valve in front of the evaporator which regulates the flow of liquid to the rear evaporator core where it turns back to gas at a lower pressure and hence gets cold.  The low pressure refrigerant then returns via the thermostatic expansion valve to the front circuit (probably the bigger diameter pipe).

The cabin air (not external air as the rear air-con just recirculates the cabin air) passes through the evaporator and is cooled due to the effect of the liquid refrigerant requiring energy and extracting it from the surrounding air then directed through the five roof vents and three air vents in the LH rear quarter trim panel.

The left hand rear quarter trim panel contains the thermostatic expansion valve, evaporator and all the fans and ducting.  Any flap would also be in there.

[marinabrid]

Hi
i put the probe into the centre row middle vent then the drivers side   both read 24c  this was with the recirc button on  as the handbook says the rear only works with that on.
the two pipes under the car are as before the same temp. both normal air temp
The chap you recommend  silver beast    stu simpson form leeds.  i called him   he thought it sounded like the expansion valve in the rear,  but this was before   i did the temp test today.   it was the fact that it was 24c   in the car    yet only 17c outside made me think that somehow some heater hot water was getting to the rear unit for it to blow out ?
can't say as i know that for a fact , air con is not my best subject !
thought maybe some vent or flap may be stuck open letting the warm water in.

[SilverBeast]

I thought the same about recirculation.

What it means for the rear is that the air drawn in to be cooled is taken from the cabin and is recirculated cabin air, so the air drawn in is at cabin temperature.

The recirculation button on then Climate Control panel just switches the air used for the front heater between being drawn from the outside, or from the cabin.

The Volvo I had before the Galaxy used to disable the air con when the recirculation function was used, I don't think the Galaxy does this though.

[marinabrid]

just reading your reply,.  i see what your getting gat,   if the air inside the car is 24c    then its that what is getting recirculated through the rear system,  but    the car had been running 30 mins with air con on and the front vents blowing cold air at 6c    so the inside of the car was quiet cool even in the rear area,    so the air drawn in wasn't 24c      i will have another measure tomorrow when the forecast for here is 20c   

[Chrispb]

Martin we spoke before about the probability of the expansion valve being the problem with your rear unit, have you had this checked out yet?

[marinabrid]

hi
no not checked,  this area has very few air con places and lots of dodgy ones

i spoke to silver beasts man  stu simpson and he thought the same as you   but he wanted Ã,£250 to travel here and replace the item and recharge.

it was just when i was in car yesterday  that i had the idea to test the vent temps.
the chap thinks also a flap could be stuck allowing warm water in    he said to test it just after start up before any heat was made by the engine   or to clamp the water supply pipes to the rear if it was hot when testing.

[marinabrid]

hi
no not checked,  this area has very few air con places and lots of dodgy ones

i spoke to silver beasts man  stu simpson and he thought the same as you   but he wanted Ã,£250 to travel here and replace the item and recharge.

it was just when i was in car yesterday  that i had the idea to test the vent temps.
the chap thinks also a flap could be stuck allowing warm water in    he said to test it just after start up before any heat was made by the engine   or to clamp the water supply pipes to the rear if it was hot when testing.

just wondered.,  if the   motor flap had stuck somewhere open or closed wouldn't it show a fault code ?

[insanitybeard]

If the air you're getting from the rear blowers is warmer than the ambient air temperature with the controls set to cold then there must be an issue either with a flap or control motor on the rear blower box, or the control panel itself but I'd expect that to throw up a fault code.

If for example a flap in the rear blower box was physically broken then the motor might still be working/moving but not actually actuating anything so you wouldn't get a fault code... I'm not sure how many flaps there are in the rear blower box but only 1 or 2 I would think, one to control the mixing of hot and cold air to control temp and maybe another to change the airflow direction from the floor vent (at the bottom of the nearside rear quarter trim) which blows out hot air- to the roof vents, which blow out cold air.

I think you've always got water (coolant) flowing through the rear heater matrix so when the coolant is up to temperature the matrix will always be hot, but when the controls are set to cold the flaps direct the blown air via an alternative path so you don't get hot air blown out.

P.S, you could always try (if you haven't already) disconnecting the climate control panel up front to see if it resets and makes any difference.

[marinabrid]

think i was barking up the wrong tree.   started up just now, inside car was 17c    air from rear roof vents was 17c with engine cold.   front vents at 6c.
as the engine got hot     the roof vents stayed at 17c ,   when you turn the heat up to 24c    the roof vents stop blowing anyway,  all the hot air then just comes from the lower floor vents at the rear of the car.

so have turned the temp up down pressed all the buttons but still have same result.
its sucking in and blowing out the cabin air temp. so all again points to this expansion valve i think.     i tested the rear floor vent temp when engine warmish and was 32c after a few mins idling, but the roof vents were still 17c   so i don't think any hot water is able to circulate in the area that feeds the roof vents anyway.

does that make sense to the experts ?

[SilverBeast]

You are correct, the roof vents don't blow hot air only cold.

I think I was mistaken in my earlier post as the three floor vents don't blow cold in mine, I think they only blow hot, which makes sense as hot air rises!

I've just rechecked my air temperatures which don't seem to have changed in the three years since the air -con pipe was repaired, with no maintenance performed.

I agree that it appears that it may be the expansion - but I'm no expert - the only other possibility I see is that someone could have disconnected and sealed the pipes leading to the rear for some reason!