Answer to Forwarded Mail: A/C info

["Jerry FIELDS" <Jerry.Fields@ccmail.adp.wisc.edu>]

     There has been considerable discussion of the A/C system used by Audi 
     since they went to the digital system in late 1986.
     
     Problems fall into 3 general categories:
     
     A/C head and related sensors (The control pannel in the dash)
     A/C programmer (little black box under the dash, passenger side)
     Compressor, over and under pressure sensors, other mechanicals.
     
     Most troublesome area is the programmer. If your temperature 
     regulates, and the location of output is the problem, the relays that 
     regulate/change the output ports may be defective. Alternatly, the 
     relays might be OK, but the vacuum servo assembly that moves the flap 
     has a problem. If you cannot get the temp to change, the problem is 
     compounded. The Bently manual for my '87 5000 CS Turbo has 100+ pages 
     dedicated to the A/C, so what follows is just a sketch of the factory 
     instructions and knowledge gained from other discussions.
     
     Remove the A/C programmer. (If you need specific instructions, let me 
     know.) Check the relays and lines for traces of oil. (Audi published a 
     service bulletin about installing an in-line filter to keep oil out of 
     the programmer; do or have this upgrade done.) If you find any oil, 
     your choices are to get a used programmer ($125.00) or a rebuilt 
     programmer ($175.00 and up.) The relays (and motor) are the same as 
     used in most '80 to '90 GM products, Caddys in particular. Audi uses a 
     Delco-built unit. The GM heads/programmers are *not* interchangable 
     with the Audi units. However, the GM programmer motor/relays can be 
     used to replace the bad Audi parts if you are handy with a solding 
     gun.  
     
     Recently, several people have checked the solder joints that attach 
     the vacuum relays to the circut board. If the relays are not getting 
     enough voltage, the will not operate correctly. Pull-in requirements 
     are higher than holding requirements. Re-solder any bad looking 
     joints, or run wires directly to the relays instead of relying on the 
     board traces to do it for you. You may also wish to check the relay 
     operation by applying power (6 - 12 volts) directly to the relays and 
     listen for the 'click' as they energize. (Relays must be in vertical 
     position when you do this, trust me.)
     
     While you are under the dash, check the regulator flap (determines 
     where air will come out) to make sure it is not rusted/corroded/stuck. 
     You should be able to operate it by hand, and a spring will return it 
     to it's default (defroster outlet) setting. Not be a bad idea to check 
     all vacuum lines for problems/splits/bad ends.
     
     If your problems also involves temperature regulation, check the 
     'Bowden' cable (attached to the motor arm of the A/C programmer) for 
     free operation. When the programmer is installed, 
     increasing/decreasing temp settings will cause the motor to move the 
     arm, regulating the temp of the output air. If this arm does not move, 
     replace the motor. On the coldest setting, the output air should be in 
     the neighborhood of 42 degrees F, measured at the dash outlet. 
     
     If your problems don't seem to be programmer related, next procedure 
     involves getting the correct manual and begin the trouble shooting 
     instructions listed. The A/C head can display error codes, and the 
     manual will tell you what the various codes mean and what to check. 
     Salvage yard heads go for $75.00 and up. (I have a spare; my problem 
     turned out to be in the programmer. Would sell it for what I 
     paid...$75.00, and I'll pay the shipping...) 
     
     Finally, make sure the system has enough freon in it. If temp 
     regulation is not what it should be, a recharge may be in order. If 
     you do this, ask the shop to add the correct amount of air compressor 
     lubricant to the system. 
     
     A/C problems are a common complaint with Audi cars of this era. Most 
     often, the programmer is at fault. With some luck and basic 
     troubleshooting, you may be able to repair a bad programmer, or 
     replace it with a used or rebuilt unit. If I can be of any more help 
     with specific details, please let me know. I just went through the 
     programmer tests/repairs on my '87 5K CST. I've also kept a number of 
     posts on this subject from other Audi ownwers; if you would like to 
     get them, I'll send them to you.
     
     Jerry Fields
     
     jerry.fields@ccamil.adp.wisc.edu