S

smac02

Member
This morning switched on the defrost, which automatically switches blower on boost and front and rear screens (my front one is u/s though). I noticed that the misting on the inside wasn't clearing on inside of front screen.
Through process of elimination I find that the defrost button doesn't switch on air con as I expected it to do. Using the outlet selection button and selecting screen then the air con will run.
Is this normal?
I'm guessing that disco's fitted with front screen heaters have the air con disabled in full defrost mode?
I also notice that using my nanocom I can disable the front screen as not fitted. Would doing this make he air con operate in defrost mode?

No time to try this at the moment but would appreciate anyone who already knows one way or the other to save me the time testing.
By the way. Could not find any threads on this, or RAVE or users manual.

Regards SM
 
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do you mean that when you press the defrost switch nothing happens? ...no change on the display, no heated rear window on, nothing? , or it goes into defrost mode just doesnt blow air on the windscreen

did you run the manual diagnostic procedure on it? (it's described in RAVE)
 
I've already run the diagnostic test with no faults shown.

I would have thought that the air con would run when the demist button was pressed. I have now set the heated front screen to "not fitted" and then give it a try on a cold morning when the screen is misted inside and see if air con runs then.
 
your aircon has a low pressure switch in the circuit which disables the compressor in the event of a reduction in pressure.it prevents the compressor clutch pack from engaging and stops the comp from burning out.When you lose pressure due to a leak you also lose oil which seizes the comp hope this helps.You can hear the clutch pack engaging when you switch the aircon off and on, have a listen under the bonnet.(takes 2 and you can do it with the engine off.
 
but aren't we talking about the defrost function which needs warm air from the matrix not compressor cooled air...the demist must work on the "Econ" mode too which isolates the clutch anyway ...what i didnt understand is what actually happens there
 
Davidmac said:
your aircon has a low pressure switch in the circuit which disables the compressor in the event of a reduction in pressure.it prevents the compressor clutch pack from engaging and stops the comp from burning out.When you lose pressure due to a leak you also lose oil which seizes the comp hope this helps.You can hear the clutch pack engaging when you switch the aircon off and on, have a listen under the bonnet.(takes 2 and you can do it with the engine off.
Click to expand...

The system is working ok. Checked the pressure in the system and it works ok when simply trying to cool the interior. It operates normally when not in full demist mode but cuts out when the demist button is pressed.

I was under the impression that the a/c system not only cooled the interior but also sensed moisture in the air and so ran to drag the moisture out of the air?

All other vehicles I have owned ran the a/c in demist mode or made it possible to select it to aid demisting the car interior, even on cold mornings.

I have tested running the settings on Lo and same result, a/c runs until I switch to demist with the button then cuts out. I have also now disabled the front heated screen, but no change in what happens.
 
on D2 it's only for defrost in cold conditions not for "demist" that's why it automatically turns the heated screens on... it doesent actually stop the aircon unit, it just switches on the defrost mode which is what you see ...full blower on the windscreen and heated screens on.
 
Ok,
But on mine it most definitely switches the air con compressor off, the clutch cuts out. Switching off the defrost button brings the air con back on, even when I direct the air flow to the screen. Would be interested to know if all D2s do the same.

SM
 
smac02 said:
Ok,
But on mine it most definitely switches the air con compressor off, the clutch cuts out. Switching off the defrost button brings the air con back on, even when I direct the air flow to the screen. Would be interested to know if all D2s do the same.

SM
Click to expand...

sorry m8, but is there a Doncaster in Africa?:D...the aircon compressor would not be activated by the clutch if the outside temperature is lower than the one you set on the screen... the clutch will engage only if the set temp. on the unit is lower than the outside temp. ... it's hard for me to explain the whole thing...u better download a RAVE and read the description and operation of the system... in a nutshell, if you are in UK your aircon now works only on the heater matrix not on the aircon compressor cos you dont need cooled air ...or do you?
 
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If I was looking for advice on the electronics of the Td5 or similar I would defo go with Sierra as he knows his stuff ;) .
As for the aircon it drags the warm air over the cold evaporator unit which is usually behind the heater matrix.The evaporator works below the dew point and when the warm air hits it the water in the air drops out, down the condensate drain and onto the road.Hence the awesome demist.As for the interaction between the aircon and the defrost function I have no clue :confused: I would imagine that the aircon would be off until the vehicle reaches a temperature that can be controlled by a stat.
Climate control however is a different ball game.It ties the heating circuit to the cooling circuit bringing in each as and when the temp set on the control panel is reached.
 
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Ahaggar said:
My Disco always turns aircon on when I use the defrost button.
Click to expand...

you mean if it's freezing outside and you have to defrost the windscreen your aircon engages the compressor clutch or what? defrost mode is an individual mode but part of the whole aircon system which will manage it according to the outside temp., the inside temp, the set temp and the chosen mode ...simple as that;)
 
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