I have the same problem, 2003 G35.

SOURCE: 2003 Infiniti G35. Radio turns off, air conditioner full blast.

Hello, The problem with the A/C controls and center console functions lies in the power circuit of the stereo unit. The solution for this is to replace the head unit via the dealership (very expensive) OR rebuild/repair your original unit. Unfortunately this is not a fix you can do at home - it does require electronic bench work.

Please feel free to contact me for more information. Our company does offer this repair service nationwide. I'm sure we can save you both time and money.

Kind regards,
Robert Cruz
[email protected]
877-4-RADIO-MD

SOURCE: 2003 Infinity G35, while driving

A/C and radio are one unit. The cheapest way out is with an aftermarket radio install kit . Look on ebay

SOURCE: I have a car 2003

Both heat and air conditioning system turns on and you cannot control climate control or the radio.But you can operate it by push buttons on steering wheels.------------ There are many other users too,facing this problem.there was a service bulletin by the Infiniti car service centers.Its a recall for this car. INTRODUCTION On some model year 2003 G35 Sedans manufactured through August 21, 2002, the audio and temperature controls may not operate as expected. When using the audio equipment or the temperature controls, the unit may become inoperative. In some cases, this can be corrected by turning the ignition switch off and back on again. In other cases, the unit remains inoperative and requires service by an Infiniti technician. To prevent this condition, Infiniti has initiated a Voluntary Service Campaign to replace the audio finisher circuit board on these vehicles. Use Infiniti Net to confirm if a specific vehicle is affected by this service campaign (P3104). IDENTIFICATION NUMBER Nissan has assigned identification number P3104 to this campaign. This number must appear on all communications and documentation of any nature dealing with this campaign. NUMBER OF VEHICLES POTENTIALLY AFFECTED The number of vehicles potentially affected is approximately 23,600.2/16 DEALER RESPONSIBILITY It is the Infiniti dealer's responsibility to check Infiniti Net for the campaign status on each vehicle falling within the range of this Voluntary Service Campaign (P3104) that enters the service department. This includes vehicles purchased from private parties or presented by transient (tourist) owners and vehicles in an Infiniti dealer's inventory. NOTE: The vehicle may also be affected by the 2003 G35 Sedan Headlamp Adjuster Voluntary Safety Recall Campaign (R2022). ----------------- For further help,click on this link directly:--- http://technoanswers.blogspot.com/2011/01/itb03-007b-infinity-service-bulletin.html ----------------- The dealer will repair it for free. as per infiniti service bulletin. This will help.Thanks.Helpmech.