1966 Blower Motor won't come on

[www.eldorado-seville.com]

Until a few days ago the ATC in my low mileage 66 worked perfectly. All functions were operating as they should.
I rebuilt the carburetor and let the car idle for a while. During this I wanted all accessories to move and also turned on the heat. It came on as always and after about 30sec the blower went off again. The power servo started to move in and out all the time by itself, but the blower would stay off. The idle speed up came on and off as well depending on the placement of the power servo. After a while it stopped doing this and stayed in the fully retracted position (full heat?). If I turn the temperature dial it does not change - but it is around freezing outside and I think this is what it should do as the sensors sense the low temperatures?

So far I checked the following things.

- Master Switch works and gets engaged by vacuum. Power is going through it as it should. Current is going in and out
- Blower Motor tested with a direct feed - works
- Blower Motor Relay - tested. Put a 12 V feed to the dark blue connector and it engages and the blower motor comes on. There is no current coming through the blue wire though..
- Power Servo - cleaned all contacts and measured the resistance in all positions  - looks good to me
- Control Head in Dash - removed it and checked the blower switches - it seems to work. I have no clue on how to check the amplifier part though? The big square resistor  is showing the 50 Ohms it should. No clue on how to test the rest and if a defective amplifier could cause a non working blower motor in all positions. Also measured the rheostat on the temperature dial, which seems to work as well.

Full vacuum is applied to the power servo, so I *think* the transducer should work.

I have no clue on how to continue troubleshooting. I have the shop manual and have ordered Cadillac Tim´s manual as well. I managed to fix the ATC on both of my 67s, my 74 and the 78 in the past, but this time I am completely out of any ideas. I do suspect the dash control as the culprit, but I do not know on how to make sure it is the actual problem. If I know it is faulty I would happily buy a working one, but I do not want to buy unnecessary parts as my car budget is very tight at the moment...

I have shot a short video explaining my problem: https://youtu.be/wbTxAWTE4vA

Looking forward to any help and tips on how to troubleshoot further. This issue is driving me nuts. What am I missing?

Thanks, Gerald

["Cadillac Kid" Greg Surfas 15364]

Gerald,
The blue wire to the blower relay is the 12 v. signal from the control head switch. 
Does the blower come on with the selector lever in either of the defrost positions? Dumb question, but have you checked the 25 amp fuse at the fuse "pane;"?
Have you checked ALL the electrical connections, and lastly, have you checked the compressor/ambient switch located behind the passenger side kick panel?
Greg Surfas

[TomB]

Another all too obvious suggestion: did you check the blower with a direct supply of 12V? And does is the motor receiving juice altogether?

Struggling with the same thing and just ordered a new pump..

Tom

[www.eldorado-seville.com]

Thank you for your replies and thoughts Greg and Tom.
@ Greg - The blower does not come on in any of the two defrost positions. It does not come on in the positions which are not fed through the relay as well. The 25 ACC fuse in the fuse panel checked out ok as well. I have unplugged each and every connector, cleaned the contacts and measured the current - they all checked out o.k. as well. I have not checked the ambient switch behind the kick panel yet - I had the impression that even if it would be bad the blower still should come on? But I will certainly check it out next - thanks for the tip!
@ Tom - yes the blower motor is still working if fed directly or through the relay - it just does not come on through the dash control... whenever I had a non working blower on my 67s it always turned out to be the master switch, but not this time... I also had defective dash units in the past, but then at least some of the functions worked...

thanks again!
Gerald

["Cadillac Kid" Greg Surfas 15364]

Gerald,
Does the compressor run?
Greg Surfas

[www.eldorado-seville.com]

I had the time to finally go through Tim's excellent manual, which is a must have for these cars.
I tested the head unit, power servo, master switch and relay and put everything back together.
I only had partial success..

I hope I can pick your brain on what is happening now... as I could not find a solution to what the system does now in any manual...
Temperature outside and inside my garage is about 40-45 degree.

When the car is cold, I can turn on the AC, and the blower works in any position of the control head.
After a while the power servo is moving towards the fully retracted (full heat) position. When the power servo arm is about half way pulled into the servo, the blower stops!
It is in the same moment the mode door and the recirculation door would change position when the blower is shutting off...
The master switch stays firmly activated all the time during this, so this does not cause the blower to stop.

When I put the control lever into the second defrost position, the power servo will constantly move in and out...and the blower will come on and off. It comes on in the AC half of the power servo, and off in the heat positions. The compressor clutch and idle speed up also kick in during this.

I have tested both vacuum actuators (mode door and recirc door) and they all seem to hold vacuum perfectly. If I unplug the purple hose at the recirculation door (there is a T connector with one end plugged)  and plug it, the whole system works exactly as it should in all modes and temperatures, but of course the recirc door won't open and close at all as it should due to the unplugged purple hose.
But otherwise it is  working perfectly!
With this procedure I am introducing a small vacuum leak to the whole system. At the end of the purple hose there should be a purge valve as mentioned in the vacuum diagram of the shop manual - could this cause a problem? There is a T and a small plastic part covering the hole of the purple hose behind the kick panel. One end of the T-is the second vacuum connector of the recirculation door - the other one is a green hose.
Could there be another vacuum problem I am missing?
Sorry for bothering you with all my questions, but I am puzzled what is going on and why my system still does not work properly!

Thanks!
Gerald

[www.eldorado-seville.com]

Finally found the problem!
Whenever I tested the master switch I checked for continuity, and it always checked out o.k.
The thing I did wrong was that I did the test by just pressing the diaphragm on the back of the switch. I heard a click and the switch had continuity.
Whenever the car was in cooling mode a weak vacuum signal was sent through the system and the switch always worked. When the system went into heating mode a very strong vacuum signal was sent through the system and the master switch was  pulled in to the maximum. Somehow the contacts then no longer have continuity. This is why the system always shut itself off when going into heat mode. I somehow missed this completely and wasted a lot of time troubleshooting. This is also why the system would work with a slight vacuum leak as mentioned in my post above. Because of the leak the switch was not pulled in that far...

I will now try to somehow fix the switch - not sure on how to fix the contacts yet, but I will try...

["Cadillac Kid" Greg Surfas 15364]

PM sent
Greg Surfas

[www.eldorado-seville.com]

I took my master switch apart and managed to fix it. My AC system is now working (almost) perfectly again. The only remaining "issue" is now that the vacuum switch of the hot water valve is stuck open. Because of this, the delay, when the engine is cold, does not work and it is blowing cold air right from the start, which is not a big problem. The hot water cut off of the valve is still working. I will need a new valve for factory correct functioning.
It took me a while to fix this problem, but I am glad everything is working again. Special thanks to Tim for all his input and his fantastic manuals.
I documented the fix on my website: https://www.eldorado-seville.com

[skinny_tom]

Thanks for posting your journey for the rest of us to learn from. Soon I will be diving into the HVAC system on a 65 Eldorado and the information here is great.

Just two questions... who is Tim? And where would one get his hands on the "manual" he wrote?

[www.eldorado-seville.com]

Tim is Cadillac Tim.
Find his website here: http://cadillactim.com
He is in this forum too.

[skinny_tom]

Thank you.

[Gene Beaird]

I took my master switch apart and managed to fix it. My AC system is now working (almost) perfectly again. The only remaining "issue" is now that the vacuum switch of the hot water valve is stuck open. Because of this, the delay, when the engine is cold, does not work and it is blowing cold air right from the start, which is not a big problem. The hot water cut off of the valve is still working. I will need a new valve for factory correct functioning.
It took me a while to fix this problem, but I am glad everything is working again. Special thanks to Tim for all his input and his fantastic manuals.
I documented the fix on my website: https://www.eldorado-seville.com

Gerald, thank you for posting this info on your weblog!!  With it, I was able to repair the inoperable blower on our Calais.  I thought it was the blower motor, we've had a rash of those here lately, and/or blower relay, since the wires to it were burnt.  After replacing the motor, and cleaning the connectors and replacing the relay, we still had no blower. 

With your info, I was able to R&R the master vacuum switch and now have air moving around in the cabin again.  The A/C still doesn't work, but didn't when I inherited the car, so it may stay that way unless I get real ambitious and upgrade to 134A, but having at least ventilation is a definite plus around here.  Thanks again!!