75ZT Community

When you switch the air-con on in our cars, I notice the recirculation mode comes on automatically and I was wondering whether that's as it should be.

For example, the outside temperature this afternoon was 26 degrees according to the car's system and my in car thermometer was registering 44 degrees.

Is it not a better idea then, to have outside air directed into the car initially to assist in rapidly bringing the interior temperature down to ambient before switching to recirculation mode?

Surely, a complete air change or two should bring the temperature down more rapidly than relying on the air-con alone?

Or am I missing something?

This function seems to me to be so that the aircon is recycling a fixed volume of ever cooler air to decrease the temperature to the that set on the ATC (Automatic Temperature Control) as fast as possible, before it starts sucking very warm air in from outside and having to cool that as well.

Just a stab in dark - consider the volume of in-car air. To allow exterior air to combine with interior air (exterior being considerably warmer than the air-con fluid (Freon?) would tend to slow down the overall drop in temp under recirculated air because in recirculating the air, it is recirculating partially chilled air. So, in terms of thermal efficiency....

Mick wrote:This function seems to me to be so that the aircon is recycling a fixed volume of ever cooler air to decrease the temperature to the that set on the ATC as fast as possible, before it starts sucking very warm air in from outside and having to cool that as well.

Agreed Mick but wouldn't it help to have the interior air replaced by air at ambient to sort of kick start the process?

Jumper wrote:Just a stab in dark - consider the volume of in-car air. To allow exterior air to combine with interior air (exterior being considerably warmer than the air-con fluid (Freon?) would tend to slow down the overall drop in temp under recirculated air because in recirculating the air, it is recirculating partially chilled air. So, in terms of thermal efficiency....

Again, see your point but still wondering if an initial rapid change of air to ambient might not be more effective to start with?

raistlin wrote:

Mick wrote:This function seems to me to be so that the aircon is recycling a fixed volume of ever cooler air to decrease the temperature to the that set on the ATC as fast as possible, before it starts sucking very warm air in from outside and having to cool that as well.

Agreed Mick but wouldn't it help to have the interior air replaced by air at ambient to sort of kick start the process?

Open the windows.

It also has to work for heated aircon so I presume having one mode of operation suits all conditions.

Mick wrote:It also has to work for heated aircon so I presume having one mode of operation suits all conditions.

Makes sense

Yesterday after lunch, I returned to a baking car with an outside temp of 32c. As always I leave all 4 doors open for a few minutes before turning the aircon on, just to give it a helping hand. It seems to cool down far faster and I don't have to endure hot seats and an unbearable atmosphere whilst the cooling takes place. I have air conditioning custom installed at home (Fujitsu) and I've found it chills down far quicker if I do the same thing. On hot days now, while I'm out I also have all the blinds and curtains drawn as well. The humidity was also very high here yesterday (a combination I detest) and to return to a fresh, air-conned environment (timer) was a pleasure and noticeably different from the one, I'd just left in the car - much cleaner somehow?

Yes this is intentional, all cars I know do it this way. The recirc mode will come on until the interior has cooled a certain amount. I guess that someone has done some testing and worked out this is the best way since it being software controlled you could do anything you want for no extra cost.

Just to let you know in case you hadn't noticed - If you switch off the Recirc the A/C still operates even though the AUTO light has GONE OUT, the same as changing the Fan Speed & Direction of Airflow - the A/C only stops functioning once you have pressed the ECON Button.
Basically, the A/C is operating as a NON-Climate Control until you hit the ECON Button.

There is also the blast factor to take into account. In a tightly confined space such as a car cabin, with, critically, your face about a foot from the vents, you get the initial impression of cold air in your face giving the illusion if you like of a different environment. So as your face and hands are (hopefully) the only areas with exposed skin, the effect works to your benefit.

a plug for Pauls ultimate remote when returning to the car in this hot weather, one press and windows and roof open releasing all the built up heat and cooling the seats down before you get in, also useful if you want to put a coat or bag on the back seat whilst the window is down,I then start the car and wait a few secs for the aircon to get going before closing the windows.