Heater switches from floor to max defrost

[seasprite]

Hey all, got a weird issue. Driving to work today the heater kept switching from floor to max defrost without me touching the temp. control. It did this a few days ago as well but finally quit when I turned the heater off, then back on after a few seconds.
Tried the same thing today but kept cycling between floor and max defrost. Since the temp. control was turned up high as it would go I turned the temp. dial back one click on the way home from work and had no issues.
When I got home I hooked up Forscan and no codes.
So any of you guys have an idea whats going on? I know the switch for max defrost is momentary switch so not sure whats triggering it. Loose plug ? Something momentarily shorting or even a bad switch?

We have a big nasty snow storm heading our way so I probably won't do to much right now. Got all your preps ready for the storm @ airline tech

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[airline tech]

Hmm - Might just be a Glitch, but as far as Max Defrost
In Max Defrost - the system automatically drives both sides to (HI) and the Blower (To Max)
it will also (Turn-On) Rear Defog & Heated Mirrors, so if this was in (Auto) in may have been confused (if you had both temps) driven to (HI)

As far as the (Mode) where it actually blows from is derived by the various temp sensors in the system. (In Auto Mode) this is why in the summer - it mostly will vent to the panels and in the winter is mostly will vent to the floor.

So - Was the (Max-Defrost) switch lighting up - In this event? or was the system simply switching vent outputs?

I would do a FCIM - Self-Test (Reset) or Pull Fuse #12 (BCM) to reset the system in case it's just a glitch.
There are 4 Temp Sensors that are associated with the system
1. Outside (OAT) - You can see this on the Sync Screen (Reading Correct?)
2. Humidity Temp Sensor - Mounted By (Right Knee) - The small inlet vent
3. Panel (Air Discharge) Temp Sensor (Mounted in the ducting of the Driver's Panel Vent)
4. Floor (Air Discharge) Temp Sensor (Mounted in the ducting of the Driver's Floor Vent)

You can only see the temperature readings with a Scan Tool (PIDs) other than the (OAT) any one of these temp sensors could cause the system to cycle the mode door actuator (in a lost state)

I would have to play with mine as I am thinking that by selecting (HI) with the temp selection it automatically selects (Max Defrost) and the (Max Defrost) button selection just automatically selects the (HI) temp for you (a short cut) to get it into (HI) - when dealing with (Automatic) system logic.

I will try this tomorrow as I am going to gas up before the weather gets crappy.

There are 3 other factors at play:
1. In Max-Defrost the (Air-Inlet) door will open (drawing in outside air) the air inlet may be cycling to close - tripping off max defrost
2. In Max-Defrost - The Rear Window Heat - is automatically triggered on - the heated window timer relay or temperature of the window - May be triggering off.
3. In Max-Defrost - The AC Compressor Clutch is commanded (ON) if the OAT is above 32 Deg,
Removes Humidity from the cabin and ties into the (Air Inlet) door, if below 32 Deg, the clutch will not engage.

 

[ryyck]

You must be the Yoda of all Rangers!!?? Much respect...

 

[seasprite]

Hmm - Might just be a Glitch, but as far as Max Defrost
In Max Defrost - the system automatically drives both sides to (HI) and the Blower (To Max)
it will also (Turn-On) Rear Defog & Heated Mirrors, so if this was in (Auto) in may have been confused (if you had both temps) driven to (HI)

As far as the (Mode) where it actually blows from is derived by the various temp sensors in the system. (In Auto Mode) this is why in the summer - it mostly will vent to the panels and in the winter is mostly will vent to the floor.

So - Was the (Max-Defrost) switch lighting up - In this event? or was the system simply switching vent outputs?

I would do a FCIM - Self-Test (Reset) or Pull Fuse #12 (BCM) to reset the system in case it's just a glitch.
There are 4 Temp Sensors that are associated with the system
1. Outside (OAT) - You can see this on the Sync Screen (Reading Correct?)
2. Humidity Temp Sensor - Mounted By (Right Knee) - The small inlet vent
3. Panel (Air Discharge) Temp Sensor (Mounted in the ducting of the Driver's Panel Vent)
4. Floor (Air Discharge) Temp Sensor (Mounted in the ducting of the Driver's Floor Vent)

You can only see the temperature readings with a Scan Tool (PIDs) other than the (OAT) any one of these temp sensors could cause the system to cycle the mode door actuator (in a lost state)

I would have to play with mine as I am thinking that by selecting (HI) with the temp selection it automatically selects (Max Defrost) and the (Max Defrost) button selection just automatically selects the (HI) temp for you (a short cut) to get it into (HI) - when dealing with (Automatic) system logic.

I will try this tomorrow as I am going to gas up before the weather gets crappy.

There are 3 other factors at play:
1. In Max-Defrost the (Air-Inlet) door will open (drawing in outside air) the air inlet may be cycling to close - tripping off max defrost
2. In Max-Defrost - The Rear Window Heat - is automatically triggered on - the heated window timer relay or temperature of the window - May be triggering off.
3. In Max-Defrost - The AC Compressor Clutch is commanded (ON) if the OAT is above 32 Deg,
Removes Humidity from the cabin and ties into the (Air Inlet) door, if below 32 Deg, the clutch will not engage.

I have an xl so manual mode only and no rear defrost.

Yes the light for max defrost would light up and blower would ramp up to max like I had selected the max setting.
I'll look at the FCIM when I get the chance.
Like you I'm prepping for winter fun, just topped off the tank yesterday. Hopefully the 12"+ of snow stays to the north of us.
At least I know what module to focus on now.

 

[airline tech]

Well, I tested it this AM, and with the Temps set to HI, it never switched to (Max Defrost) and the Rear Window Heat never triggered on but after some time it did start cycling the air, the mode door never moved as it stayed @ 49% but the internal doors were shifting the air around.
As it was in (Auto) and distributing the air as it needs to get the overall cabin temp to, I assume 90 Deg as the cabin temp (selection) is at 5 Deg increments and one step below shows 85 Deg.
If I hit the (Max Defrost) button the Mode Door drove to 100% & Rear Defrost triggered on.

So, it is possible with your issue, the (Max Defrost) button may be sticking or thinking it's being pressed.
Note: You mentioned (Pulsed) yes, it is momentary pulse button as I confirmed with my scanner for (Max Defrost Status) it will only show (On) during the button press and then shows off, but if you view the PID in a graph - you can see it is actually on via the Graph View
Still playing with my new scan tool and learning its functions (operation)
So, this tells me for some reason your system thinks that the (Max Defrost) button is being pressed.

 

[seasprite]

Well, I tested it this AM, and with the Temps set to HI, it never switched to (Max Defrost) and the Rear Window Heat never triggered on but after some time it did start cycling the air, the mode door never moved as it stayed @ 49% but the internal doors were shifting the air around.
As it was in (Auto) and distributing the air as it needs to get the overall cabin temp to, I assume 90 Deg as the cabin temp (selection) is at 5 Deg increments and one step below shows 85 Deg.
If I hit the (Max Defrost) button the Mode Door drove to 100% & Rear Defrost triggered on.

So, it is possible with your issue, the (Max Defrost) button may be sticking or thinking it's being pressed.
Note: You mentioned (Pulsed) yes, it is momentary pulse button as I confirmed with my scanner for (Max Defrost Status) it will only show (On) during the button press and then shows off, but if you view the PID in a graph - you can see it is actually on via the Graph View
Still playing with my new scan tool and learning its functions (operation)
So, this tells me for some reason your system thinks that the (Max Defrost) button is being pressed.

Well today when I drove to work with the temp. control 1 click from max temp. no problems. So on the way home I set the temp. to max and you guessed it no problems.

Maybe something with the switch position was causing the issue and when I adjusted the temp setting, made the world right again.
If it starts up again I will take the scanner with me and try to capture it happening as long as I choose the right PIDS or Forscan has the right PIDS to choose from.

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