A/C Mystery Ford Focus '12

I have a mystery for you. I have a '12 Focus and for no apparent reason the A/C will turn off and warm air enters the car for 1-3 minutes and then returns to normal cold A/C air. It doesn’t matter if it’s on “max A/C” which will circulate the air inside the car or just the coldest setting on the A/C, high fan, low fan, it just happens. What usually happens is that I’m driving 40 or 45, then have to slow down (stoplight, etc.) and speed up again, during the slow down is when the A/C turns off and warm air enters the car. As soon as I’m driving 45 again for a minute it usually kicks back to cold air. OR, while driving on the freeway at 60 - 70mph after about 15-20 minutes it all of a sudden stops cooling and I get warm air in the car. It’s been checked by 2 different dealers already 4 times and they never found anything wrong with the A/C System. It did have an actual leak a few weeks ago and that got repaired but it still has this mysterious behavior. Does anyone have any idea what is causing this strange behavior? Given it’s already almost 110 degrees here in Phoenix, you can appreciate the importance of consistent A/C!

Don’t know what the dealers checked concerning the a/c …but…
2 more ideas.
If the a/c system itself checks out, have them check the radiator fans.
Are they coming on as they should ? If not , the computer defense mechanism will turn off the additional load drawn by the a/c.

Another angle;
The a/c evaporator ambient temp switch.
If the evaporator is getting TOO cold , it will shut off the compressor while it thaws a bit.
Either a bad switch or it really is getting too cold and frosting up.

The compressor is controlled by the powertrain control module (PCM) aka computer. It gets inputs from a number of sensors such as engine vacuum (MAP sensor) and the cooling system temperature (ECTS) and probably 8 or so more. If any of them go outside there parameters, it will shut off the compressor.

When the AC shuts off, is your engine temp gauge a little high? That could be the source of the problem. One solution for this would be an aux transmission cooler as the transmission contributes a lot of heat to the radiator.

When it happens on a surface street, see if you can duck into a parking lot and pop the hood to see if the compressor is running.

Thanks all, I will check your suggestions or have the dealer check it again. Might take a couple of weeks to get around to it but if I find the source/ problem I’ll update it here.

Plus, if ambient temps are to blame…Phoenix, or should I say , the city is to blame
In-city conditions accentuate the already high air temps .

ADD to the 100 plus air temp ;

  • Radiant heat being produced by all the asphault and concrete paved surfaces absorbing and reflecting u.v. energy.
  • Traffic ; produces it’s own heat index when you add all the vehicles in close proximity to each other.
  • the slowness of all those vehicles grouped together in light-to-light or bumber-to-bumper conditions.
    The temperature just two feet up from the ground is a very different animal than the air temp reported by the weather man.
    These conditions are often the cause of overheating otherwise not a problem for the individual vehicle.