Problem Fixed. I had my CX9 AC switching from cold to normal air between trips intermitently abour 2 to 3 timea a week and sometimes goes ok for weeks. The dealer did not find any codes. This went on for 6 monthe. After extensive search over months I found the problem and it was infront of my eyes. The Outside ambient temprature sensor located in front of the rediator. I saw a negative reading right under the RPM on the dashboard. It was sifnaling the compressor to go off. Replaced and now all ok

 

Nice work!

Yes they go out more often then not. Unless you look at your local weather and compare the dash temperature with the value of the weather report most would never catch that.
Surprising to read the service department did not catch and or think to check that sensors that also effects the HVAC system if it is faulty.

 

Mostly because When I take it to service, ac is ok. It does not switch while driving only between start of car and not all the time. The surprise is that it has no codes or code history.

 

It's not uncommon for the ambient air temperature to give false reading and not show a DTC. Yet it does affect a few ECU controlled system on a Mazda. The area it is mounted is generally environment protected but it does get very dirty depending on some operating locations and weather. These go bad so often that most well-known retail auto parts carry many part numbers and brands in stock.