RL1990

I’ve had my truck for a few years but I just noticed that the A/C does blow colder when you use Max A/C.

Normally on full cold and recirculate the lowest the temp goes is about 39-40 according to a vent thermometer. Which is considered good and shows adequate performance. But if I turn on Max A/C it will go to 34-35.

The manual just says use for maximum cooling and recirculated air. All this time I thought it was just a shortcut for turning on max fan and recirculate. I used to use it only when it was really hot just cause it said Max A/C not thinking it made a difference just desperate to cool it down. But most of the time I just crank the fan all the way up without using it. Recirculate is automatically turned on anyway.

Turns out it also allows the evaporator to get colder before cycling the compressor and that 5 degree difference is noticeable.

My guess is the higher temperature without Max A/C is to eek out a little more MPGs while still providing adequate performance. But you need to use Max A/C for...maximum A/C performance just like the setting says. Very sneaky Ford.

Maybe this is old news but I just figured it out. It’s a “well duh” moment for me that I thought I would share.

deapee

That’s a really good tip. Do you have any sources for the info you provided?

idrive

iTrader: (3)

I have to RESPECTFULLY disagree.

SoPoSassquatch

It'd absolutely make sense to allow the suction to drop lower before cycling the compressor if it's a manual engagement. Should only be using it when the load is very high so you don't need the same protections you do for defroster.

Cool!

RL1990

Just the old style probe thermometer you stick in the vent. The air is a about 4-5 degrees colder on Max. The reasoning is just a guess in my part because Ford is trying every trick in the book to improve fuel economy.

SoPoSassquatch

It'd absolutely make sense to allow the suction to drop lower before cycling the compressor if it's a manual engagement. Should only be using it when the load is very high so you don't need the same protections you do for defroster.

Cool!

jwmustang

All vehicles do that.
The reason its colder is because its cooling the air thats in the vehicle and not the outside air before it gets sucked into the vehicle. If the vehicle was sitting in the sun for a while its best to open the windows to let the heat out then the ac wont have to cool 130 to 150 deg temps.

A/Ox4

iTrader: (1)

If you want to grab a few more temps, you can modify the coolant system with a few simple steps.

Here is a video I made on the idea, but this was when I had a 7.3L Powerstroke. The idea is the same. Ford included this feature on some Rangers and all Excursions.

Flamingtaco

Checking vent temp does not tell you what the compressor is doing. You have to put a gauge on the lines to see that.

Turning off recirculate is naturally going to result in lower vent temps as you are no longer adding warm outside air to the intake.

Doing what you suggest requires replacing a cheap pressure switch with more costly pressure sender and sensing circuit. That doesn't fit with the fact that the system already inherently only uses as much energy as is requested.

As the cabin cools, the temperature of the air moving through the evaporator drops, transferring less heat back into the refrigerant. resulting in lower refrigerant pressure.

Compressor cycling determined by a low pressure switch... as the cabin cools, and therefore refrigerant pressure drops, the system reaches the low limit earlier, resulting in less compressor run time.

Same for the ambient temp... as outside temperature increase/decreases, system pressure does the same (due to less/more cabin heat transferred to the environment due to the difference in temp between the refrigerant in the condenser and the outside temp).

The system already works on demand and as needed with cheap, simple switches.

35º at the vents is a bit low, the air at your core is going to be 32º or colder, and core freeze can occur. I'd check the line pressures and make adjustments to get it closer to 40ºF. I presume you made these checks on an 80ºF or hotter day.

D2Abbott

Our trucks utilize an expansion valve to regulate system pressure as opposed to a "CCOT, Cycling Clutch Orifice Tube" type system that cycles the compressor clutch to regulate system pressure.

When MAX A/C is selected:

• the air inlet door closes, preventing outside air and allowing only recirculated air.
• the recirculated air indicator is illuminated (recirculated air forced on).
• the air distribution doors operate simultaneously to direct airflow to the instrument panel registers. A small amount of airflow from the floor duct is present.
• the temperature door moves to the full cool position. The air temperature is adjustable.
• the A/C button is illuminated.
• the A/C compressor operates if the outside temperature is above approximately 0°C (32°F).
• the blower motor is commanded to the highest speed, but can be manually adjusted if desired.