HVAC Mod

My old Honda had separate on/off buttons for the AC and for recirculation. My new Ford is pretty unsophisticated and doesn't. The AC comes on with AC, Max AC, and Defrost. Recirculate automatically comes on with MAX AC.

I was thinking of adding a switch(es) to turn off the AC and/or turn on the recirculation - basically manual override. This would allow me to shut off the AC when I don't want it on and to turn on recirculate in any HVAC position (vents, floor, defrost, etc). AC on defrost, for example, isn't always necessary.

I'm not sure how to activate recirculation yet, but to deactivate the AC switching the AC pressure switch or the compressor clutch would work. Any reason not to do either of those?

People often want to turn on recirc, but I've never found the need myself. As for AC. a toggle switch in the compressor clutch wire would do the job. Might set codes that will confuse the climate control module, though.

Max AC is the exact same thing as recirculate.

Not at all. Max AC runs the AC, shuts off coolant to the heater core (at least for certain Fords), and recirculates the cabin air. Recirculate just recirculates the cabin air. Recirculate is useful if your commute takes you past a water treatment plant or diesel exhaust, which mine does. I use it all the time.

I use is a fair amount on my Colorado. For the P71, when things get stinky, I just flip to Max and let the compressor run. Off the top of my head, the recirculate door on the P71 is vacuum operated but I won't swear to that. You might want to see what your new Ford uses. Vacuum operation might make using a simple switch a little difficult.

Recirc is usually not 100% recirc though (still pulls in a little outside air), so shutting the system off for a minute in a stinky area can be better.

Realistically, recirc is most useful with A/C to cool things down faster when the car is heat soaked on a hot day.

Apis Mellifera wrote: AC on defrost, for example, isn't always necessary.

Under what circumstances would you use defrost and not want to remove humidity?

APEowner wrote:

Apis Mellifera wrote: AC on defrost, for example, isn't always necessary.

Under what circumstances would you use defrost and not want to remove humidity?

You wouldn't need to if it's already very cold out (the air will be plenty dry after being heated). However, the A/C will already not run in that situation, as the system pressure will be too low for the compressor to cycle on much if at all once it's below 25* or so outside.

You probably want to check that what kind of compressor your car has. A lot of new cars have gone to a variable swash plate instead of a on/off clutch.

Could still be done but as mentioned previously it could cause trouble codes in the HVAC module and possibly the PCM.

When I start my car and it's 115F outside and 140F inside, I want outside air coming into the cabin, because it's cooler than what's in there. Recirc stays off.

As soon as the cabin temperature gets below the ambient temperature, recirc goes on.

My Fiesta has two buttons as stated.

All along I thought max air include recirc. Found out that is doesn't, must use recirc. for quick cool down etc.

Ford says I should run Max AC when ever using AC, more efficient.

EvanR wrote: When I start my car and it's 115F outside and 140F inside, I want outside air coming into the cabin, because it's cooler than what's in there. Recirc stays off. As soon as the cabin temperature gets below the ambient temperature, recirc goes on.

Open the windows for the first minute or so to equalize the temp. After that, recirc will cool faster as it's repeatedly cycling the air in the cabin, rather than cooling hot outside air and then pushing it into the cabin (which pushes some of the already somewhat cooler air out of the car instead of allowing it to get cycled through again and cooled further).

In reply to rslifkin: Leave a 1/4" gap open in your windows when you park. Does wonders for decreasing the heat accumulation inside.

jharry3 wrote: In reply to rslifkin: Leave a 1/4" gap open in your windows when you park. Does wonders for decreasing the heat accumulation inside.

Yes it does, but only when you can trust it not to rain!

Also make it easier to unlock the door by some one other than the owner.