ecu conditions requred to swicth on A/C

[Tony747]

hello peoples,

iv got a 2016 ford ranger px2 manual (T6) with a 3.2l 5cly diesel engine.

my issue is the air conditioning clutch will not activate when it's demanded,
untill he car is driven for a few minutes,

I can manually activate it by grounding the relay,

but during the time it won't turn on, I don't have any power of either side of the a/c fuse

I believe I have narrowed it down to the ecu has to have "condition met" and then signals the pcm to active the a/c circuit..

my question is for someone smarter than me is
does anyone know what conditions need to be seen by the ecu before it actives the a/c circuit

any help is much appreciated

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[airline tech]

(2) inputs the PCM looks at - Outside Ambient and Evaporator Core temp to control the AC Clutch.
If one of those inputs in incorrect, then the clutch will not engage.

Now, being that you say it operates after driving a few miles.
The Outside Air Temp - will update withing a few miles, this may be a factor.

But I suspect you have a Freon Charge issue or a AC Pressure Issue from the Pressure Switch.
As you drive it, you are warming up the engine bay, and this may be triggering the Pressure Switch to pick up the correct pressure reading.
A faulty pressure switch will keep the clutch from kicking in.

 

[Jason B]

What airline tech said.
Low refrigerant will prevent the AC clutch from engaging.

 

[Tony747]

the refrigerant gas has been checked and within factory spec,

sometimes when you first start up the car the air con will work ( randomly, can't seem to work out it's pattern)

and then the other time when it won't switch on when demanded, after a few minutes of driving it will kick in the clutch compressor and it will be fine for hours.( can switch of the car for a short period and it will work as per normal )

it goes back to playing up after the ignition has been off for a few hours.

 

[pinky89]

Hi,

dod you ever work out what the problem was? I have the exact same issue however ford has been unable to work out the problem.

thanks
Jason

 

[airline tech]

It could be a number of factors, but if you are only having issues after it sits overnight or a long period of time.

Leads me to think of a few possibilities:

1. Ambient Temp or EVAP Temp Sensor - improper reading would be the primary sensors but the PCM factors in the other sensors on the truck as well and if it sees a imbalance between the sensors it disables the clutch - so all of these sensor (PIDs) needs to be compared on a cold engine they should all match within a few degrees.

2. Faulty AC Pressure Transducer (Switch) - This reading needs to be compared (Scan Tool - PID vs Manifold Gauge) on a cold engine, if AC System was recharged to a manifold gauge set (Is the AC Pressure Switch) seeing the same pressure as the gauge set- it MAY be reading a lower or higher pressure than the actual system pressure. Variance allowed is 15-PSI between the 2 readings,
The improper low pressure reading of a cold engine (compares the Ambient Temp and a Predetermined programed value) of what the operating low pressure limit should be.

So note how the Temperature Sensors provide the PCM (Temperature Input) data and the PCM uses that data to determine what should the AC Pressure be - The inputs tie together for the AC Clutch operation.

Once the engine has been running - the system pressure increases (heat induced) and the AC System begins to operate.

The above are some likely things to check that the dealer may not be looking at and or seeing if you were to drive to the dealer and have them check the system after the engine has been running.

3. Sticking AC Clutch Relay - not closing when the relay is cold, this is a possibility, but with the issues showing mostly on a cold engine (if this is true) leads me to think a pressure or temp sensor issue that is increasing temp or pressure as the engine bay heats up.
(Rises to the minimum required) Pressure or Temp needed to engage the clutch

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