Fixing the 1978 Cadillac Eldorado´s ATC programmer. The AC works again.
****UPDATE****
An update to the article below can be found here as I had to repair the programmer again in May 2015:
The air-condition in my 1978 Biarritz did not work correctly. For some reason the system always stayed in full AC mode and no matter to where I put the temperature dial on the control head I could not get the heat on, no matter what I tried.
The shop manual is very helpful in trouble shooting the system. Its covered in the 1977 factory shop manual (FSM) as there were no changes made to the system in 1978.
It took me a while to fully understand how the system works - so I had to read the FSM multiple times to get the grip what is going on in the system.
First I inspected all the vacuum lines in the car to make sure that there was no leak anywhere, as the heating mode requires a very high vacuum at the vacuum motor in the controller.
All lines were in very good condition. I also checked the control head connections in the dash which were good as well.
I then suspected the vacuum motor in the programmer as it did not move. I removed the programmer from the car. You can access it from underneath the dash on the passenger side or even better if you remove the glove box lining through the glove box.
From there you only have to unscrew 5 screws, unplug the wires and the vacuum lines to get it out.
When I had it out of the car I checked the vacuum motor. I just sucked air through the hose and it moved and held vacuum perfectly.
The transducer or the amplifier in the programmer were most likely the problem.
When I checked the transducer which regulates the vacuum supply to the vacuum motor, I noticed that it seemed to not be connected to the electrical board as it should. I pressed it in, so that it made good contact with the board again and put the programmer back into the car and connected everything again.
***UPDATE 2015 - its not connected with pins but soldered to the circuit board - 3 of this soldering points were broken - the “repair“ I made here only temporarily worked. You have to check the soldering points for a permanent fix***
I started the car and the AC came back to life again immediately. I could see how the vacuum motor went through all the modes as it should according to the position of the temperature dial on the control head.
The build quality of the programmer obviously is not very good and the transducer somehow came loose causing the ATC to not work as it should. ***Update 2015 - it did no come loose but the soldering points broke***
After I tested everything I put the parts back together and can now enjoy a full working ATC in my 78 Biarritz again ;-)
The programmer as seen through the glove box with the connectors and the plastic case removed
The 1977 / 1978 Eldorado MK II Automatic Temperature Control Programmer
The transducer which caused the problem (the golden part with the single vacuum line going into it)
The transducer is connected to the electrical board through a couple of pins - it was not connected properly and somehow became loose over the years - that was why the system did not work.
***UPDATE 2015 - its not connected with pins but soldered to the circuit board - 3 of this soldering points were broken***
The vacuum checking relay and the electric connectors.
The vacuum power motor
from the 1977 FSM
Trouble shooting guide for when the system works in full AC mode only.
A color coordinated electrical schematic with annotations to describe the various functions of the system.
1966 Cadillac Coupe deVille (15)
1967 Cadillac DeVille (54)
1967 Cadillac Eldorado (71)
1971 Lincoln Continental Mark III (23)
1974 Cadillac Coupe deVille (45)
1978 Cadillac Eldorado Biarritz (24)
1996 Buick Roadmaster (19)
Car Shows (53)
Cruising (4)
For Sale (3)
Garage Stuff (32)
Pacer (1)
Restoration (137)
Various (55)
Video (16)
Website News (30)
- 6 way power seat
- 8-track
- 10 Ohm
- 429
- 1932
- 1957
- 1958
- 1958 Cadillac Eldorado Seville
- 1958 Cadillac Repair Tip
- 1959 Cadillac Eldorado Seville
- 1964
- 1965
- 1966
- 1966 Cadillac Coupe deVille
- 1966 Cadillac Repair Tips
- 1967
- 1967 Cadillac DeVille
- 1967 Cadillac Eldorado Repair Tip
- 1967 Cadillac Repair Tip
- 1967 Eldorado
- 1968
- 1970 Cadillac Eldorado
- 1971
- 1971 Lincoln Continental Mark III
- 1974
- 1974 Cadillac Coupe DeVille
- 1974 Cadillac Repair Tip
- 1976
- 1977
- 1978
- 1978 Cadillac Eldorado Biarritz
- 1978 Cadillac Repair Tip
- 1980 Cadillac Eldorado Biarritz
- 1996
- 2012
- 2014
- 2017
- 2018
- 2019
- 2022
- 2023
- 3063206
- 7027235
- 7800483
- 7805675
- 7805676
- 12355706
- 17058531
- 17059968
- 17059969
- 22010515
- 22010661
- A.I.R
- A6
- AC
- AC Compressor
- AC Electrical Diagram
- ACC
- Accelerator Pump
- Accelorator pump
- Actuators
- Adriatic Blue Metallic
- Ads
- Aftermovie
- Air Pump
- Aircondition
- AIRPUMP
- ALC
- Alternator
- AM
- AM-Transmitter
- Antenna
- Anti Rattle Clips
- Antique Gold
- Arizona Vintage Parts
- Arrival
- Article
- ASC
- Ash Tray removal
- ATC
- Atlantis Blue Firemist
- Austria
- Austro Classic
- Autolite SP-459
- Automatic Seat Back Release
- Award
- Banner
- Barn Find
- Battery
- Battery Tray
- Beach Race
- Bearing
- Bendix
- Biarritz
- Bigfoot
- Bill Hirsch Engine Enamel
- Bleeder Screws
- Blower
- Bolts
- Borg
- Brake Booster
- Brake Fluid
- Brake Gray
- Brakes
- Broken Bolt
- Brougham
- Bucket seats
- Buick
- Bumper End
- Bushings
- Cadillac
- Cadillac BIG Meet
- Cadillac BIG Meet
- Cadillac birthday cake
- Cadillac Blue
- Cadillac Color Selections Dealer Book
- Cadillac Coupe deVille
- Cadillac Dealer
- Cadillac Meeting
- Cadillac Mini Meeting
- Camaro RS
- Caorle
- Car Show
- Carburetor
- Card
- Carpet
- Carter AFB
- Cavalry Twill Vinyl
- CB
- CBM
- CCCD
- Choke
- Christmas
- Citizens Band
- Classic Cadillac Club Deutschland
- Clay Towel
- Cleaning
- Clock
- Clockwork
- Clutch
- Clutch Coil
- Collector
- Colonial Yellow
- Color Coded Springs
- Commercial
- Compound
- Compressor
- Condenser
- Continental Mark III
- Control Head
- Conversion
- Convertible top
- Coolant
- Corona
- Cowl
- Cruise Control
- Cruising
- CV Boots
- CV JOINTS
- D6230
- Dash Trim
- Decal Removal
- Decals
- Decoration
- Dehumidifier
- Delco Moraine
- Der Standard
- detailing
- Deville
- Diagnosis Chart
- Diagram
- Dial
- Digital Rotary Drum Clock
- Diner
- Disc Brakes
- Distributor
- Diverter Valve
- Door Jamb Switch
- Door Rubber Conduit
- Dornbirn
- Dot3
- Drive Shaft
- Driving tour
- Drum brakes
- Dry Ice Blasting
- Dry Ice Cleaning
- DVD
- Eastwood
- Eldorado
- Electric Choke Thermostat
- Electrical schematic
- Elvis
- Engine Bay
- Ep
- Epoxy floor
- Europe
- Evaporator
- Exide
- Factory Markings
- Fender Skirt
- Floor
- Flushing
- Foam
- For Sale
- Front AXLE
- Front brakes
- Front bumper filler
- Front Floor
- Front wheel bearing
- Fuel Filter
- Fuel Pump
- Fuel Sending Unit
- Fusible Link
- Garage
- Garage Cabinets
- Gasket
- GE
- Gear indicator
- General Time
- Glove box light
- Grand European
- H4
- Haus of Hot Rod
- Headlight Actuator
- Headlight doors
- Headlights
- Heater Core
- Heater Hose
- Heater Valve
- High Idle
- Holley
- Honest John
- Hood
- Hood Emblem
- Hood Ornament
- Hose Clamp
- Hot Choke
- Hot Water Valve
- HotRod
- How to
- Hödlmayr
- Ignition Diagram
- Illuminated Entry
- John D‘Agostino
- John Foust
- Klassikwelt Bodensee
- Kremsmünster
- LaSalle
- Leather seats
- Light Switch
- Limited
- Lincoln
- Lincoln Mark III Repair Tip
- Low Mileage
- Magazine
- Marilyn Monroe
- Mark III
- Master Cylinder
- Master Switch
- Master Vacuum Switch
- Media Blasting
- Meeting
- Meguiras
- MK II
- Mobile
- Model
- Moldings
- Mom
- Mopar Nationals
- Mostkost Kustom
- Movie
- Neon
- NOS
- Oberösterreicher des Tages
- oilchange
- ORF
- Overspray
- Pacer
- Paint
- Paint correction
- Paintjob
- Part Number
- Parts
- Patch Panel
- Perfect Circle
- Permabag
- Persian Lime
- Photo shooting
- Photoshooting
- Pictures
- PinUp
- POA Valve
- Power Antenna
- Power Servo
- Power Vent Windows
- Power Window
- Printed Circuit Board
- Programmer
- Pulley
- Quadrajet
- Quarter Panel
- Quartz Conversion
- R134
- Radiator
- Radio
- Rattle
- Rear brakes
- Rebuild
- Recalibrate
- RediRad
- Reed Switch
- Relais
- Relaunch
- Removing Overspray
- Repaint
- Repair
- Restoration
- RIP
- Roadhouse
- Roadmaster
- Rochester
- Rocker Arm Cover
- Rocker Panel Extension Clips
- Rostio
- Rotary Valve
- Rotterdam
- Rupes
- Rust removal
- Rust removal gel
- Sabre Wheels
- Sand Blasting
- Sandblasting
- Screed
- Season Greetings
- Seasons Greetings
- Seat Back Locks
- Seat Padding
- Seat Transmission
- See through ornament
- Self adjusters
- Sepp's Garage
- Seville
- Sheetmetal
- Shocks
- shop manual
- short
- Sign
- Solenoid
- Spark Plug Wire Routing
- Speakers
- Special Award
- Speed Bleeder Screws
- Splash Guard
- Starter Diagram
- Starter Motor
- Steering Column
- Storage
- suction throttling valve
- sunroof
- suspension
- Swirl Mark removal
- Switzerland
- T3
- Taillight Cover
- Texan´s Choice Award
- Thermostat
- Tilt and Telescope
- Time capsule
- Tomsclub
- Torque Specifications
- Tower Hose Clamp
- Towtruck
- Transducer
- Transmission
- transmission control selector
- transmission control selector indicator light
- transmission shift indicator
- Treadle Vac
- Treffen
- Tri-Band
- Troubleshooting
- Trunk Cardboard Kit
- Trunk lining
- Trunk to bumper cover
- Turn Signal Switch
- TV
- Typisierung
- Ultimate Garage
- Underbody
- Undercarriage
- Undercoating
- Undercoating Removal
- Vacuum Booster
- Vacuum diagram
- Vacuum hoses
- Vacuum Master Switch
- Vacuum Schematic
- Vacuum Valve
- Valve Cover
- Various
- Vent Window Switch
- Vibration
- Vibrator
- Vicodec roof
- Video
- Vinegar
- Vinyl Roof
- Visitor
- Washer Fluid Float
- Washer Fluid Low Level Indicator
- Water Pump
- Wax
- Weatherstripping
- Website News
- Westclox
- Wheel Bearings
- Wheel Housing
- Wiesbaden
- Windlace
- Winter
- Wiring
- Wiring Diagram
- Wonderbar
- Workbench
- Zurzach