Air Con issues
Thread Starter
Junior Member
Joined: Sep 2009
Posts: 46
Likes: 1
From: Adelaide South Australia
ML320
Air Con issues
G'day people and a merry christmas and a happy new year.
Ok I have an A/C problem and would like some guidance before I resort going to a dealership.
A/C started cold "freezing" when first bought about 2 years ago. Since then the perfromance has got steadly worse until this month had no a/c at all.
Diagnosed no/low refrigerant. Regassed and was then diagnosed that the tx valve was not working. Replaced tx valve, receiver drier and all the seals attched to them. Regassed.
Now i can get cool air, not cold. Temperature of the day 24.5 (as read by the dash gauge) dec C, air at outlet = 19 dec C
Conditions are:
Temp control max cold
Fan position 1
Recirc off
Elec fans are NOT engaged
Hard wire fans as a test for continous operation has no effect on temp.
Turn RECIRC on and the temp climbs to about a 2 deg difference between outside and inside
Freeze the in dash temp sensor and the temp goes to max as expected.
(The blend motor seems to be moving it's full range from what I can see)
Are there any more sensors I can disable or bypass to see if I can narrow down the issue?
Thanks for any ideas
Bob
Ok I have an A/C problem and would like some guidance before I resort going to a dealership.
A/C started cold "freezing" when first bought about 2 years ago. Since then the perfromance has got steadly worse until this month had no a/c at all.
Diagnosed no/low refrigerant. Regassed and was then diagnosed that the tx valve was not working. Replaced tx valve, receiver drier and all the seals attched to them. Regassed.
Now i can get cool air, not cold. Temperature of the day 24.5 (as read by the dash gauge) dec C, air at outlet = 19 dec C
Conditions are:
Temp control max cold
Fan position 1
Recirc off
Elec fans are NOT engaged
Hard wire fans as a test for continous operation has no effect on temp.
Turn RECIRC on and the temp climbs to about a 2 deg difference between outside and inside
Freeze the in dash temp sensor and the temp goes to max as expected.
(The blend motor seems to be moving it's full range from what I can see)
Are there any more sensors I can disable or bypass to see if I can narrow down the issue?
Thanks for any ideas
Bob
Thread Starter
Junior Member
Joined: Sep 2009
Posts: 46
Likes: 1
From: Adelaide South Australia
ML320
Air con issues
An update. Having run the car with a thermometer on board I have now discovered the following. Without a/c, at max cold the temperature will climbb above outside temp. (blend motor flap issue?) with a/c on the aicon will pull down to 17deg c, but between the white temp mark and full cold there is no temperature change. Only when you go beyond the white mark and up that a temp change will start to occur.
Conclusions: (1) The blend motor/flap is not fully closing, (2) the variable resistor that controls the temp is u/s, (3) the a/c push button module is not working.
any more thoughts?
Thanks
Conclusions: (1) The blend motor/flap is not fully closing, (2) the variable resistor that controls the temp is u/s, (3) the a/c push button module is not working.
any more thoughts?
Thanks
Last edited by sweeper; Dec 18, 2011 at 05:08 AM. Reason: spelling, grammer (A lost art I know )
Thread Starter
Junior Member
Joined: Sep 2009
Posts: 46
Likes: 1
From: Adelaide South Australia
ML320
Ok another update. Stripped the dash out, upper and lower 
I can now take a decent look at teh aircon. The blend motor seems to be working ok. The only issue is that the motor/flap deosn't actually open fully(?) So i removed the motor and moved the flaps through there full range. It seems that they were never moving to full heat. Pulled the motor apart and found nothing broken. Reset all of the gears and now get a full range of motion from full heat to full cold. Now the only things left are (1) the ac push button module or a sensor still bad. I'm also running it at idle with full air and a hot day 40dec C plus to see if the fans come on. more updates to follow. One more thing, when the motor is at full heat, the stepper motor is still, but when in full cold the motor "chatters" constantly. incipant failure?
Well the fans do come on and the a/c shuts down! The inlet and outlet pipes to the evaporator core were too hot to touch.
I can now take a decent look at teh aircon. The blend motor seems to be working ok. The only issue is that the motor/flap deosn't actually open fully(?) So i removed the motor and moved the flaps through there full range. It seems that they were never moving to full heat. Pulled the motor apart and found nothing broken. Reset all of the gears and now get a full range of motion from full heat to full cold. Now the only things left are (1) the ac push button module or a sensor still bad. I'm also running it at idle with full air and a hot day 40dec C plus to see if the fans come on. more updates to follow. One more thing, when the motor is at full heat, the stepper motor is still, but when in full cold the motor "chatters" constantly. incipant failure?Well the fans do come on and the a/c shuts down! The inlet and outlet pipes to the evaporator core were too hot to touch.
Last edited by sweeper; Jan 1, 2012 at 02:41 AM. Reason: additions
