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What is acceptable air conditioner outlet temperature?

I have a 1996 Nissan Maxima. It was about 95 degrees today (measured with my own thermometer not what the weather report says), and my air conditioner outlet temperature was reading about 50 degrees. that would be temperature differential of about 45 degrees. I had the fan on second lowest out of 4 settings and on recirculation.
<br/> Does that seem reasonable?
<br/> I had the car for about 4 years now, and the air conditinoner had been all right when I first bought it, but it has been progressively getting warmer. Today, when the outside temperature was registering 95, the car interior would not get cooler than 80. Even when I drove for 20 minutes on the freeway.
<br/> Is there an easy way to check whether the air conditioner is working properly?


  • edited July 2010
    Approx. 40 degrees F is what you're shooting for.

    Have a qualified mechanic check it out.

    Older cars will loose refrigerant over time and require a "recharge" at some point.

  • edited July 2010
    I've read manuals that stated a 45 degree temperature drop is normal and acceptable; however, I don't buy that at all.
    My feeling is that the outlet temps should be down in the high 30s/very low 40s at a minimum on a 90 degree day.
    Some years back on my now gone Mercury I had the A/C on that one putting out 25-30 degree air on a 100+ degree day although I consider this one more of an anomaly.

    The best thing that can be done is to connect a full gauge set and see what's going on with the pressures on both the high and low sides. If the pressures are fine then one should consider the possibility of a blend door not functioning correctly.

    You might also raise the hood and look at the evaporator outlet fittings, the accumulator, etc. for condensation. If there's any humidity to speak of you should see these parts sweating and there should be a constant condensation drip under the car if the A/C is functioning even halfway like it should.
  • edited July 2010
    Me being from GM have been trained to figure in the humidity but the practice draws much "flack" here. Use a few degrees above what low side temp is.. Take a look at gague head you will see that temp/pressure is roughly porportinal for both R12 R134A.
  • edited July 2010
    I agree that low side system pressure is a good indicator of the outlet air temps. If someone has 50ish PSI on the low side then they have a problem in my opinion.

    The car is 15 years old and odds are that it's a bit down on the refrigerant charge due to leakage.
  • edited July 2010
    My 1999 Camry got down to about 42*F on a 95*F day system on recirc and full fan.
  • edited July 2010
    My '97 Escort hits 40 pretty much regardless of the temps (max I get is about 100).

    I recently had a general purpose shop (my mistake) evacuate & recharge my Silhouette AC - they assured me that with such a large system (front & rear w/ about 3lb refrigerant) the 50 degrees from the vent on a 90 degree day was about as good as it would get. Bunk. I'm going to get it to the local specialists. I think you should too.
  • edited July 2010
    Personally I don't think a 45 degree drop is unreasonable. The temp out the vent will be dependent upon the ambient temp. The system only removes heat, and its capacity to do so is finite, meaning that as the ambient temp rises so too does the vent outlet temp.

    One thing it also does that makes it seem more efficient is that it removes moisture also. The dried cabin air doesn't seem as hot, becuause it has better capacity to absorb moisture from your skin which is how your body dissipates heat.
  • edited July 2010
    NOone in the AC biz uses how much drop you get as a parameter in judging AC performance. Not how GM, or BMW taught me, where did this method come from?

    It is not part of the ASE cert. test I took and passed, or the refridgerant handling class or the Community College class, or the GM FSM.

    And your perception of how good a job is done has the humidity of the air around you as one of its parameters.
  • edited July 2010
    Checking the vent outlet temp is part of the job according to the factory service manuals on the cars that I've been involved with although I don't consider it to be the first priority.
    First thing is to connect the gauges and see what the high/low pressures are. Checking outlet temps should be saved for a test run down the road after everything is buttoned up.
  • edited July 2010
    Some of us (myself included) seem to have missed an important point:
    "I had the car for about 4 years now, and the air conditioner had been all right when I first bought it, but it has been progressively getting warmer."

    Since the performance of the system seems to have deteriorated, an automotive AC shop visit is in order. Only hands-on can the performance of the system be evaluated.
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