AC blows warm air intermittently

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05-07-2015, 01:55 PM

Blake P

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AC blows warm air intermittently

Over the past couple days during my ~40 mile commute I have noticed the air conditioner in my Q7 blowing warm air intermittently. It will be blowing nice cold air then all of a sudden it will blow warm (probably outside temp) air for a couple minutes, then back to cold air. 2 days ago when I first noticed it, it happened twice during my commute. Yesterday it only happened once. I dropped it off at Audi this morning and they said the freon was a little low so they filled it up, but said there were no error codes or anything else that was obviously wrong with it. My first thought when it started blowing warm air was the condenser since my A4 once took a rock to the condenser that put a small hole in it and required replacement. The difference was that once my A4 started blowing warm air it never cooled down again. I searched the forum and didn't find any similar issues in here, but figure maybe one of you has had this issue in the past and didn't document it. Any advice would be appreciated.

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05-07-2015, 02:48 PM

Kris Hansen

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I would suspect low refrigerant as well. Keep an eye on it, but the recent recharge should do the trick I'd say. The systems are designed to shut off the compressor when the refrigerant levels are too low, I believe based on pressure.

It will also cut the compressor based on temperatures as well.

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05-14-2015, 03:11 PM

idua7

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I have similar issue with my 2015 Q7 and it's in the shop right now because of this. It would blow cool air in the front and warm air in the back after 15-20 minutes driving. I have been taking it back and forth to the Audi shop 4 times already but nothing has been done beside refilling freon because they can't find any "ERROR CODE".
I even dropped off my vehicle at Audi when it was blowing warm air in the back but still they could not find anything wrong beside saying freon is little low given the car is only few month old.
I still experience this issue after they refilled the freon.
They were trying explain to me how the A/C system works when it reached the setting temperature, but failed to explain why it blows cool air in the front and warm air in the back with auto setting.

Any suggestion what's next step for me if they are unable to find the root cause?

Thanks.

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05-14-2015, 08:48 PM

lx4life

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Are you sure the car is not just adjusting the temp in the car by adding warm air since it might be too cold. Just a thought.

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05-14-2015, 10:44 PM

Blake P

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Quote:

Originally Posted by Kris Hansen

The freon recharge appears to have solved the problem. They pressure tested the system and found no leaks, so hopefully that's the end of it.

Quote:

Originally Posted by idua7

Damn, keep us posted.

Quote:

Originally Posted by lx4life

Are you sure the car is not just adjusting the temp in the car by adding warm air since it might be too cold. Just a thought.

This is one of the possibilities my SA initially suggested, but I'm pretty sure that wasn't the case.

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05-15-2015, 02:16 AM

smith2010Q7

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Quote:

Originally Posted by idua7

If there is a complaint at only the evaporator in rear heating & A/C unit on vehicles with two evaporators, first perform cooling performance testing at front A/C system => [ Test Requirements ] See: Front A/C System Performance, Checking\Test Requirements. If cooling performance at front is OK, check cooling performance at rear A/C system. If, during cooling performance testing on rear A/C system, it is detected that performance is not sufficient and then no cause for the complaint can be found, check line connection between evaporator in question and exit of line connection at distribution point of refrigerant lines in left front wheel housing (for example, for constriction). If the fault cannot be found, bring vehicle to a workshop that has the necessary tools and in which the work can be performed accordingly by qualified personnel.

¤ There is no sensor that measures air temperature downstream of evaporator installed in rear heating & A/C unit, compressor performance control is performed therefore only via the measured value of Evaporator Vent Temperature Sensor (G263) which is installed in front heating & A/C unit. Under certain unfavorable conditions, it may occur therefore because of this that the temperature set on the rear heating & A/C unit is not attained during normal regulated operation even though the A/C system is OK. Also it may occur that for example, on an A/C system on which the specified outflow temperature has already been attained in the front heating & A/C unit and maximum cooling output is requested at rear A/C system, the rear outflow temperature is a few degrees °C higher than when a high cooling output is requested at front A/C system (if necessary increase front cooling output via setting at front).

Vent temperature on the evaporator, depending on the outside air temperature (measured air temperature on left rear vent temperature sensor and right rear vent temperature sensor)
B Ambient temperature
C Permissible tolerance range
The air temperature measured by left rear vent temperature sensor and right rear vent temperature sensor must be the same or a maximum of 5 °C (41 °F) higher after 5 minutes than the specified vent temperature at evaporator, depending on ambient temperature (see diagram).

¤ If the A/C system is OK and the same temperature is reached on both evaporators (inside the front and rear A/C), then the temperature on the front evaporator is displayed in the measured values block for the Climatronic control module (measured value from the Evaporator Vent Temperature Sensor (G263) ).

¤ The air travelling from evaporator to vents is heated slightly by heat radiated by heater core in heating & A/C unit and by leaking air which flows by at temperature doors through the heater core.

If the required values are not reached in either display fields, then check the measured values from the left rear vent temperature sensor and right rear vent temperature sensor and the activation of the Right Rear Temperature Door Motor (V314) and Left Rear Temperature Door Motor (V313) using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding". If the fault cannot be found, bring vehicle to a workshop that has the necessary tools and in which the work can be performed accordingly by qualified personnel (there is a fault in the refrigerant circuit).

If the values required are obtained only on one side, check measured value of sensor, Left Rear Vent Temperature Sensor (G405) or Right Rear Vent Temperature Sensor (G406) , which has the measured value not in the permissible range. If measured value is OK, check function of control motor and temperature door operation for the side where the measured value is not OK (Right Rear Temperature door Motor, refer to => [ Right Rear Temperature Door Motor (V314) ] See: Service and Repair\Removal and Replacement\Rear HVAC Components\Right Rear Temperature Door Motor (V314) or Left Rear Temperature door Motor, refer to => [ Left Rear Temperature Door Motor (V313) ] See: Service and Repair\Removal and Replacement\Rear HVAC Components\Left Rear Temperature Door Motor (V313)) using Vehicle Diagnosis, Testing and Information System VAS5051 in the "Guided Fault Finding" function. If no malfunctions can be determined here, check air duct in rear heating & A/C unit, refer to => [ Air Duct In Rear Heating & A/C Unit ] See: Air Door\Description and Operation\Air Duct In Rear Heating & A/C Unit.

Q7 Right Rear Temperature Door .pdf

Q7 Left Rear Temperature Door .pdf

Q7 Air Duct In Rear Heating & A:c.pdf

Now the manual said check with VAG which that's what the tech did, my opinion when checking doors to see if they open I like to removed the trim panel and make sure everything is hook up correctly. I also like to check to see if they move. The VAG is reading the motor not the door inside, so if the motor is ok then the door might not be. Now still being under warranty Audi cannot replace a part unless a code is present. In the TSB it will say recharge.

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05-15-2015, 11:35 AM

idua7

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Just got back from the Audi dealer and as expected nothing wrong was found. I was not convinced and we did a couple tests with the lead technician. It's a little cold here this morning in SoCal, the outside temp is around 56 degree.

Here are the test results:

1st test on my Q7:
A/C set to 67 for all zones (auto mode). After about 15 minutes, the front was blowing at 75 degree and the back at 82 degree. At the beginning they seemed to blow at the same air temperature, we didn't feel much different.

2nd test on another Q7 (2012 model):
A/C set to 67 for all zones. After about 20 minutes, the front was blowing at 68 degree and the back at 75 degree.

The big difference between the tests is on the first test, it blew warmer air and stronger on the side rear vents and you can feel the warm air a couple feet away, whereas in the second test, the rear didn't blow the same air temperature as the front but not as warm and strong as from the first test. You have put your hand up close in order to feel the air.

It looks like the second Q7 was able to attain closer to the setting temperature than in my Q7. The lead technician think it’s working normal in my Q7 and described the front and back A/C systems as Smith provided above and stated that the air has to travel around car and through different components before blowing to the rear vents and therefore, it’s warmer in the back. In another word, I have to set the temperature in the front much lower than I want to get cool air in the back.

I’m very disappointed if this is how Audi designed their cars. Have any of you experienced this condition in your Q7? Even my kids are well aware of this problem and often asked why it’s blowing warm air.
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AC blows warm air intermittently

AC blows warm air intermittently

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