[W126 Coupe] Air Conditioning Diagnosis

[Dick Spellman]

Dan Landiss wrote:

> on 6/11/2007 4:07 PM Dick Spellman wrote:

>> So, was the low side pressure within spec based on outside ambient 

>> air at the time you tested?

>

> I have no charts. It turns out that "25F" on the gauge coincides with 

> "25psi" on the low pressure side. I'm afraid you are right about the 

> air flaps.

>

>> There is also the much difficult to get at (with pass airbag) vacuum 

>> element that directs air flow between center vents and defrost 

>> vents.  This too fails and you hear the blower running at high speed 

>> and feel little air in the cabin.  That's because it fails over to 

>> the darn wind screen when the leak on the diaphragm occurs.

>

> Switching from the maximum cooling position (up and down arrows on the 

> button are both white) to the next position (is it white for the down 

> arrow only?) definitely changes the air flow. The former results in a 

> LOT of air on the windscreen, and the latter almost none.

>

Hi Dan:

Please view this link and dependent on the refrigerant you are using 
(please let me know) see if your 25psi reading was in spec for 90F 
outside on the day you tested low pressure.  Also was the car at idle or 
at 1200-1500 rpm when testing?  If you can, let me know what the engine 
coolant was reading too and when was visco clutch last replaced (miles) 
and did the electric fan ever kick on???  Does compressor stay engaged 
over say a 10 minute period or is it cycling on and off with frequency? 
<http://www.autoacforum.com/aacf/ptchart.cfm>

On any vent temp checks, I'd suggest you run in MAX AC, recirc mode, 
window down, engine at 1200rpm, engine to normal operating temp.  Then 
read outside air, low side pressure, and vent temps.  It's okay to run 
at MAX with fan on low (especially if you suspect the recirc flap is not 
working as it should) to get the center vent readings.  Also, on low fan 
close the left & right mechanical slides to move the cooled air over 
just the center vents.

Dick

btw: I am only proficient as a diy'r on r-134 systems