Chrysler Repair: 1988 Chrysler LeBaron Heater And A/C Problems, 1988 chrysler lebaron, chrysler lebaron

Question
I have a 1988 LeBaron Convertible Deluxe with the digital A/C and heat controls. I cannot control the vents, all the air comes out at the floor, and I have no temperature control, all the air comes out cold. This problem came on all of a sudden. I cannot find a vacuum leak. What should I do to diagnose this?

Answer
Hi Patrick,
Check the fuse #2 under the dash. Then let me know if that is OK. The diagnosis is based on the detailed symptoms and some self-diagnostic capability built-in to the ATC controller. There is enough detail that the only efficient way to share this information is to xerox copy and postal mail you the 12 pages from the shop manual. So check the fuse and then if that isn't the problem use the "thank/rate" tab to get back to me without having to wait for me to be available for a question. Use the comment section to give me a postal mailing address. If after you get the pages you would be so kind as to send me back four 42-cent stamps to cover the copy and postal mail costs that would be appreciated.
Roland

So here is the update. The fuse is good. The problem with the heat was low coolant. I still have the problem of not being able to turn on the dash vents. The air comes out of the floor fine, and if you have just started the car, then it will come out of the dash. Once it stops coming out of the dash vents it can be put to come out the floor only. Thanks for you previous prompt response.....

Hi Patrick,
The vacuum line is what provides the power to direct the air doors. It is similar to that used in the non-atc units.  Have you tried disconnecting the vacuum line from the power/vacuum module itself and measuring the vacuum with a vacuum gauge while the engine is running? Then turn the engine off and see if the vacuum will be maintained for 2 minutes. If not, then the vacuum check valve is stuck open and needs to be freed-up or replaced. That valve is necesssary to maintain the vacuum of the system when you step on the gas, which otherwise drops the manifold vacuum.  That check valve is located in the vacuum supply line above the a/c housing behind the dash. It is in the line that comes thru the fire wall. Also check the attachment of the vacuum line at the power brake booster. If all that checks out, then check out the vacuum mode switch module itself.
Thanks for the nomination.
Roland