still warm rear air con

[marinabrid]

i suppose I'm lucky the front air con is still cold,  the rear air con only works in recirculation mode,  today i put a air con cleaner bomb through the car,  turned the recirc on and left it 10 mins running on full. the front is still cold  i was hoping for the rear roof vents to be cold also    but no   still getting warm air only through them even with the rear setting on low, any more ideas welcome on this topic.

[Chrispb]

Have you felt the rear aircon refrigerant pipes when running? like the front system one should be icy cold the other warm/hot.
The rear system also has an expansion valve that may be blocked.

[marinabrid]

have been under car,  have traced the air con pipes from the rear to near the centre of car where they disappear ,  they are the same temp   so for some reason the problem must be from the front end thats stopping the cold air getting to the back  do you think ?

[insanitybeard]

Or like Chris says a blocked rear expansion valve is preventing circulation of the refrigerant gas around the rear air con circuit.

[marinabrid]

i suppose that then is a job for the expert at a high price,  where is this valve and whats it look like ?

[Chrispb]

The valve is adjacent to the rear evaporator I am not an expert on aircon so get an opinion from a specialist, but I do know the valve can cause this problem.

[insanitybeard]

I believe it's number 10 on this diagram.

[marinabrid]

thanks a lot for the pics  think i will just be happy with the front cool.

[marinabrid]

just looking at the pics,  if this valve was faulty and stopping the gas getting in   would one of the supply pipes be cold  up to the valve,   as it is both pipes are the same temp that go to the unit. 

[Chrispb]

Probably not as your not getting a flow, personally I would get an opinion from a specialist in your area.
Gas will need removing if your thinking of changing valve.

[insanitybeard]

No, I don't think the pipes would be getting hot/cold in that part of the circuit- as Chris says if the valve is blocked then the air con gas isn't circulating ('flowing') through that part of the circuit properly- therefore it's not passing through the expansion valve at the rate it should (or indeed at all), or expanding and 'absorbing heat' via the rear evaporator. Because of this, the pipes won't be getting cold on one side of the evaporator, nor hot on the other. It's a little bit like a radiator with an airlock- the water can't flow through it, so it stays cold, as do the pipes.

[marinabrid]

would any fault show in the vcds check,  nothing shows as a code in the Auto HVAC section,  there is another block called HCVS REAR  but for some reason the controller won't reply

[Mirez]

HVAC Rear isn't used on the Galaxy as the rear unit hasn't got it's own controller, its all done from the front unit.

[SilverBeast]

I believe the liquid flowing to the valve would be warm.  It's the expanding (when it turns from liquid to gas) that takes the heat put of the air, so the return pipe would be cold, not the feed.  If it's blocked the liquid wouldn't be flowing any way so I would expect both pipes to be around Ambient anyway.  I believe the back system is in parallel to the front, if the back is blocked all the refrigerant will flow through the front - it might even let it get even colder if you want!

[marinabrid]

Thanks for all the input chaps i don't think for the way i use the car its worth spending perhaps a lot of cash  when the front works,   its useful though to know how it works.

[insanitybeard]

I believe the liquid flowing to the valve would be warm.  It's the expanding (when it turns from liquid to gas) that takes the heat put of the air, so the return pipe would be cold, not the feed.  If it's blocked the liquid wouldn't be flowing any way so I would expect both pipes to be around Ambient anyway.  I believe the back system is in parallel to the front, if the back is blocked all the refrigerant will flow through the front - it might even let it get even colder if you want!

Interesting you say that, I've just had a little read up on the principles of operation of an air con system, my understanding of the particulars was a little back to front! I knew it involved adiabatic cooling, but I wrongly assumed the pressurised gas flowing into an expansion valve would be cooler than the expanded gas coming out of it..... I'm better educated now! 

[marinabrid]

afraid im lost on it !  not much understanding of air con at all 

[Chrispb]

Possibilities are that there could be debris in your system either from a failing air dryer or compressor, the colour of the old  oil is a good indication of how the system is (according to my local aircon chap) if the oil is clear that's good, if it's black it's contaminated.
Of course it may just be the valve is faulty but it could be blocked with debris.

[SilverBeast]

Interesting you say that, I've just had a little read up on the principles of operation of an air con system, my understanding of the particulars was a little back to front! I knew it involved adiabatic cooling, but I wrongly assumed the pressurised gas flowing into an expansion valve would be cooler than the expanded gas coming out of it..... I'm better educated now! 

Could be wrong (It's not unkmown! ).  I'm only going on the basis of what happens at work.  We have liquid nitrogen and liquid C02 tanks that are fed into our temperature chambers. When it is released via a solenoid into the chambers it can expand, which allows it to turn back into a gas.  This is what removes the energy from the air, hence cooling the chamber.  It does mean the chambers end up filled with Nitrogen or CO2 gas though.  They can get down to less than -40C though!

[SilverBeast]

The diagram at the top of the page on this site http://berryhilltesting.co.uk/about-us/air-conditioning/ seems to explain it fairly well.