Is there a tech writeup somewhere that lists the conditions under which the AC compressor runs or does not run? For example, if the AC is toggled on via the hard key (on the auto controller as opposed to manual) and the heater is on, say it's 40* outside, when will the controller kick the compressor on/off? I am assuming there are times it does run when the heater is on, like defrost for example. Are there other conditions?

If the AC hard key is toggled off, will the compressor not under the above circumstances?

TIA.

 

Since you did not specify which climate control system you have I'll assume you have EMTC. From the WSM for EMTC (Electronic Manual Temperature Control):

A/C Request

When an A/C request is received by the PCM, the A/C clutch relay is engaged when all of the following conditions are met:

• Excessively high or low refrigerant pressure from the A/C pressure transducer is not detected.
• Ambient air temperature is above approximately 32.0°F (°C).
• Evaporator temperature is above approximately 33.8°F (1°C).
• Engine coolant temperature conditions are within normal parameters.
• Wide Open Throttle (WOT) condition is not present.
• Engine torque conditions are within normal parameters.
• Battery state of charge conditions are within normal parameters.

Compressor control and the evaporator temperature are a function of many parameters, not just a straight on/off, to avoid freezing the evaporator. The PCM monitors multiple temperature sensors for correlation including, but not limited to, AAT, CACT, CHT, ECT, IAT, MAF, MAP, and MAPT (as applicable). The PCM runs this logic after an engine off and a calibrated soak period of 6 to 8 hours. This soak period allows the Ambient Air Temperature (AAT) sensor and the other temperature sensors to stabilize and not differ by greater than a calibrated value, typically 18ºC (32.4ºF). If a temperature sensor input is found to be reporting a temperature imbalance the PCM does not allow the A/C clutch to engage. For more information on PCM sensors, refer to Powertrain Control/Emissions Diagnosis (PC/ED) manual.

The PCM monitors the discharge pressure measured by the A/C pressure transducer. The PCM interrupts A/C compressor operation in the event the A/C pressure transducer indicates high system discharge pressures. It is also used to sense low charge conditions. If the pressure is below a predetermined value for a given ambient temperature, the PCM does not allow the A/C clutch to engage.

 

Amazing, thank you. My bad for not specifying that I have a ‘19 Lariat crew with the “auto” dual-zone controller. When I refer to the auto key, I mean the momentary toggle on the auto controller.

i am asking this because I intend to piggyback a secondary air to water cooling system for my intercooler on the factory climate control system. The way in which I combine this with my existing conventional air to water aftercooler is largely dependent on the way the factory climate control system functions.

i appreciate the info.

 

The DATC (Dual Automatic Temperature Control) basically operates under the same parameters.

 

Air to water, or air to gas, as in an A/C intercooler? Or are you misting the intercooler? Or...? Need details...

 

It's essentially a brazed plate heat exchanger which is using the refrigerant loop to cool down his supercharger coolant.
The now colder coolant flows through the superchargers intercooler to create a better cooling affect than a traditional air to water system.
A few different aftermarket companies out there that have kits. It's a pretty cool concept. Basically what Dodge Demon's use from the factory.

Here's a schematic I drew a while back: The one Sharkhunt is planning to go with is a different make than mine but again similar concept.

 

Thanks for the detailed information.

Seems like the "manual" system isn't very manual after all. There seems to be a lot of computer logic used to operate the manual HVAC. I always thought that my A/C seemed to operate differently depending on temperature. When it's a mild day the A/C works but doesn't seem as cold as I know it can get even on full cold. However on a hot day it blows ice cubes. I theorized that when the computer sees mild temperatures it reduces compressor output because it doesn't have to get as cold to maintain a comfortable cabin temp and it saves fuel. However on a hot day it runs the compressor wide open for the evaporator to get as cold as possible.

 

What Ecks said, I am doing something very similar to what he is doing but with a different manufacturer and slightly different routing.

Information so far has been pretty clear regarding the conditions of when the compressor is activated versus when commanded by the climate control.

The other information I am looking for includes the conditions when the auto dual zone controller will command the compressor activation other than the obvious “because you have it set to cool” - I.e. defrost, dehumidify, that kind of thing.

 

Didn't the Raptor or Mustang do something similar? I remember reading a number of years back about Ford putting a secondary A/C evaporator on the intake manifold of an upcoming model for short cooling bursts.

Used to be, they would just go off high side pressure and throttle demand. That works pretty good, but can not account for frozen evaporators, high energy draw, or fast temperature swings on mild days. That last one, I often have an issue with. I like a nice 69º at all times. When it's in the mid 60's out, doesn't take much time for the a/c to take out the sun load heat. I'd end up fiddling with the temp setting several times on past vehicles as I'd overshoot the temp repeatedly. I've noticed the 150 appears to take about the same time dropping the temp when it's in the 70's as when it's in the 80's, and just a little longer in the 90's. I actually like this as I now fiddle with the controls less.

Of course, this may occur due to differences between the vehicles that have nothing to do with climate monitoring and controls.