AudiWorld Forums - Blowing hot air all the time

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Blowing hot air all the time

Hi I'm new. Bought a 2008 q7 3.0 tdi 2 weeks ago. When i bought it the a/c didn't work. After changing a leaking pipe i had it gassed up and it worked fine but today it will only blow hot air no matter what temperature i set the climate control to. It does get hotter when set to HI but still puts out quite hot air when set to LOW. The econ light hasn't come on which makes me think the a/c is ok. Any common issues i need to know? Cheers, Matthew.

Does the compressor engage/kick in?
Both too LOW and too HIGH refrigerant charge will prevent it from engaging.

Who did the charge up for you? Take it back and have them put gauges on it again and see where it stands.
If it was just a week they should check it and give some ideas. My hope would be 'it worked for a week' and stopped would point to charge level Low/High

On a really hot day it will read HIGH without ever running just because of the outdoor ambient temps raising the pressure. It is a fairly tight window for Low -> PROPER -> High (over charged) That overcharged situation can make you scratch your head because it works every now and then.

Thanks for the reply.
Am i right in thinking if there was a pressure issue the econ light would come on because it senses a fault, like when i bought it and there was no charge in the system?
The air thats coming out the vents is hotter than the ambient air which makes me think its possibly a climate unit issue?

Thanks for the reply.
Whats confusing me a little is the air coming out the vents is hot when set to low, hotter than the ambient air outside? Also before i had it gassed up the econ light was on due to the lack of pressure in the system, i plugged computer in and it confirmed this with a low pressure fault but the econ light hasn't come on which makes me think it could be a faulty climate unit?

Yeah I experienced this exact thing from 'over charge'.
HVAC (and I am not a tech) works with super heating refrigerant. So it is my theory in 'my situation' that the compressor came on for just a little while and tripped the high pressure switch and this caused the refrigerant to get super hot but it didn't run long enough to go into sub-cooling therefore it only spit out super hot air as that is what was in the evaporator coils that the air was blowing over.

Ok here is a simple check you can do to confirm 100% your a/c system is working or not without a/c guages connected. Depending on your engine arrangement, if you can see the 2 aluminium pipes coming from a/c compressor, this will be your (hot) high pressure side & your (cold) low pressure return side. If your cold pipe looks wet & cold to touch then it is working and the same with the hot side to touch.
If they both feel like their the same then your compressor is disengaged.
high pressre cut off will be from either over charged or restriction in the line. Your a/c will never work until the problem is fixed as this is to protect the system.
low pressure cut off will be from an undercharge or a leak. Same thing applies.

the a/c unit in the cab is a HVAC design which means it always has the heater running aswell as the a/c system but the 2 circuits are separeted but an electric door flap, this is how changing the temperature is controlled by allowing the door to open slightly and allow heated air the mix with a/c evaporated air.
If your (DOOR) is jammed open which is very common on hvac syrems this will be causing the vents to blow continuous hot air.
just start by firstly seeing if your a/c system is pumping when the settings are in the low position as described earlier, if the a/c is off then you will need to take it back to the guys that charges the system.
see how you go

Im taking it back to garage that charged it. Ive plugged computer in and the pressure sensor is reading 6.4 bar and im assuming this is the high pressure side. Question is is that the correct pressure?

Hey mate. I would say with the 6.4bar which is about 93psi either your compressor is off or it is extremely low on gas pressure and not high!
pretty much every a/c under charge pressure from the a/c compressor will be somewhere from 120psi upto 200psi whilst running. Things change such as ambient temperatures etc but 93psi would be more like a total sytem pressure charge with the a/c off.
like you said taking it back to them is the best to getting it sorted.

Yes this was the pressure with engine off. Didn't change with the engine running either but according to the real time data the compressor was running at something like 60% but i couldn't tell if the compressor was working to look at. The pipes going in and out the compressor were both the same temperature, like ambient temperature not hot or cold so the gas is definitely not circulating.