'69 Eldorado...Help With No Heat and Dash Control Problem...

[69eldo]

Well, another project to tackle.....The heater in my car has never worked since I bought it, doesn't blow hot or warm air. The system also doesn't turn on in either the low, auto or high settings unless you first go all the way over to defog or deice and then back to those settings. According to the service manual diagram, I did find that the vacuum lines were routed incorrectly at the master switch and also the two lower ones at the heater control valve were reversed, but changing those didn't seem to help at all.

Any help would be appreciated. Not sure where to start? 

Thanks!       

[Bob Hoffmann CLC#96]

Start by shooting the engineer that designed  it! LOL The system is like a string of early Xmas tree lites. One thing fails & the whole system shuts down. Worst case you should be able to run the blower manually & get some heat. Sorry ,but that's not possible with the design. They're a real PITA. Bob

["Cadillac Kid" Greg Surfas 15364]

Welcome to the Wonderful world of mystery.  Grant, if the system does operate after you cycle the lever to defrost or de ice, and if the temperature control does work on cooling, meaning it cycles the fan and the temperature to maintain conditions in the car you are in great shape.  IF the previous is true and all you lack is heat I would look for a (manual valve) hot water shut off  in the heater lines that is closed.  Not finding that I would suspect a bad heater water valve OR and this is highly likely, a leak in the control vacuum lines or incorrectly installed vacuum lines.
The shop manuals for that year are very straight forward, and if you follow them you will be able to work through the problem.
The symptoms sound very much like a vacuum leak or leaking vacuum valve.
By the way, these systems were so far ahead of the competition in 1969 and were state of the art.  Before the era of dependable electronics there was just vacuum, electricity and manual actuators.  I for one think the engineers who developed the control systems did a masterful job given the tools they had to work with.
Greg

[TJ Hopland]

My 75 does that sometimes.  I have not had time to dig into it yet.  It would seem to have to be somehow related to the engine temp circuit.  At first I assumed it was a bad switch just not letting the fan turn on but then discovered that going to defrost and then back to the auto settings.   The switch is located on the right head behind the alternator.  When the metal temp of the engine reaches something like 120*F it grounds the wire which then tells the system that there should be enough heat in the engine to blow heat.  I was going to look into that circuit to see if there is some sort of relay that has to latch or if its some other electronics that could be causing this issue.   I was just thinking of temporarily bypassing the temp switch to see if perhaps it had a marginal connection but somehow going to the defrost mode would activate the circuit and the marginal connection was still enough to hold it. 

[Dave Shepherd]

By going to defrost you are overriding the cyl head temp switch in the circuit, once the blower relay is activated by doing this, even bringing the lever back off defrost does not disengage the blower relay, part of the oe design.

[TJ Hopland]

Dave, so it is literally a relay that is 'latched' by either going to defrost or the temp switch?  I assume a power cycle would un latch it?  If everything was working properly and the temp switch did activate but then cooled to the point of deactivating the blower would still run?   That would make some sense from a design standpoint.  I have several service manuals from that era but am 'on the road' and they are not with me.   It looks like both of us could be dealing with bad temp switches or connections to them?

["Cadillac Kid" Greg Surfas 15364]

Guys,
Grant's '69 has a bimetalic valve in the heater valve as the temperature turn on via allowing vacuum to close the Master switch. When you turn the lever to defronst on your '75 you are activating the high speed blower relay.  We are mixing metaphors here.  The '69 and '70 were unique..\
Greg

[TJ Hopland]

So the engine temp switch thing started in 71?   Were the 68&9 just sort of the first generation of the 70's system or were they totally their own thing?

I have a friend with a 69 but have only replaced a relay and connector that had something to do with the blower.  I did not dig too deep into the book, I just replaced the melted parts.

["Cadillac Kid" Greg Surfas 15364]

68, 69, and 1970 saw a few changes in the controls and the control strategy. Many although significant are nearly "invisible".  1971 saw some major changes that were carried through 1976 nearly unchanged, until the state of the art of electronics and electronic actuators improved enough to be reliable in an Automotive environment.
Greg

[69eldo]

Welcome to the Wonderful world of mystery.  Grant, if the system does operate after you cycle the lever to defrost or de ice, and if the temperature control does work on cooling, meaning it cycles the fan and the temperature to maintain conditions in the car you are in great shape.  IF the previous is true and all you lack is heat I would look for a (manual valve) hot water shut off  in the heater lines that is closed.  Not finding that I would suspect a bad heater water valve OR and this is highly likely, a leak in the control vacuum lines or incorrectly installed vacuum lines.
The shop manuals for that year are very straight forward, and if you follow them you will be able to work through the problem.
The symptoms sound very much like a vacuum leak or leaking vacuum valve.
By the way, these systems were so far ahead of the competition in 1969 and were state of the art.  Before the era of dependable electronics there was just vacuum, electricity and manual actuators.  I for one think the engineers who developed the control systems did a masterful job given the tools they had to work with.
Greg

Thanks Greg! I've certainly got myself a project trying to get everything working correctly on this old girl. I've also been in contact with "Cadillac Tim", he's been a great help clarifying a few things for me. I spent a few hours today checking vacuum lines and electrical connections with no luck. I did check under the dash and all looks good there as well, didn't hear any "hissing" or apparent leaks. As far as what works.....the air distribution functions all work (AUTO, LOW or HI only after setting lever to DE FOG or DE ICE and then back ), the a/c compressor works, the servo is working moving the arm in & out at different settings/temps. One thing I noticed while in the AUTO, LOW or HI setting is that the master switch shuts off the system after a short time. It stays running in the DE FOG or DE ICE mode.

I just went out again to make sure the other settings were working and the thing blew warm air for the first time when I initially turned it on? I had been driving it around earlier, but has been parked for an hour or so. After the warm air blew out of the system, it went back to cool.  Where did that warm air come from?

I suppose with all these vacuum operated accessories and such that any vacuum leak at all could cause a problem? I'll keep trying and hopefully find something.

Thanks again,
Grant

["Cadillac Kid" Greg Surfas 15364]

Grant,
The fact that the master switch goes off after a short period would lead me to think you have a vacuum leak "someplace".Check all the connections carefully. A bad connection often looks good until you look closely.  \
The warm air you talk about sounds like the system going to heating which might occur, again with a leak in the vacuum control circuit.  Take time and check out each component.  When you find and fix the problem you will be glad you did.
Greg

[bill henry]

my 70 has the blower turn on switch on the head

["Cadillac Kid" Greg Surfas 15364]

Bill,
The 68-70's were in an era of change engineering wise.  When they went to a heater turn on via the sensor in the right cylinder head they eliminated the master switch (unless you have one on yours and in that case please let us know).  There were multiple "mid model" changes to track down and eliminate the gremlins in the Automatic Temperature Control.
Greg

[69eldo]

Bill,
The 68-70's were in an era of change engineering wise.  When they went to a heater turn on via the sensor in the right cylinder head they eliminated the master switch (unless you have one on yours and in that case please let us know).  There were multiple "mid model" changes to track down and eliminate the gremlins in the Automatic Temperature Control.
Greg

My '69 has both, the heater turn on switch in the right cylinder head and the master switch on the blower/evap housing. The service manual shows both also. I'm wondering if those heater turn-on switches were a common problem on these cars? 

["Cadillac Kid" Greg Surfas 15364]

At the risk of sounding human I have to admit that I was unaware of the combination of the two devices.  To eliminate the possibility of a bad thermal sensor (rt head sensor) you can just ground the wire that leads to it.  If this causes the system to function correctly you have found your Gremlin.  Replacements are availaible.
Greg

[TJ Hopland]

I have not yet run into a bad switch.  Bad connections yes.  Unconnected seems most common, I assume they got knocked off while working on the alternator.

Does the 69 have the vacuum parking brake release?  On the later cars thats the line that also goes to the heater.  Maybe the control for the parking brake is leaking a bit at times not letting full vacuum to the heater system?   Do the 68's have any sort of a vacuum canister with perhaps a faulty check valve?

If you do end up getting a replacement sensor for the head be sure to get the correct one,  there is an identical looking one (on the later cars for sure) on the other head (left rear) that is for the stop engine temp light.  The stop temp one turns on at something like 260*F vs the 120*F range of the heater control one.  I dont remember the exact temps but you get the idea.

[69eldo]

Greg, I'll try grounding that wire just to see if it changes anything. That would be nice if that all it is!

TJ, yes it does have the parking brake release and it works fine. I didn't hear anything that sounded like a vacuum leak while under the dash with the car running.

I'll keep digging and will find it yet!

Thanks guys!



 

[bill henry]

the 70 does not have the master switch that i can see. it has a blower relay

[TJ Hopland]

What I was thinking with the parking brake is to check it in all the gears in case its a worn valve/switch causing the leak only in certain gears. You would have to do some thinking to figure out how to do this safely.

[69eldo]

Just to be sure that I have this hose routing correct at the master switch, can anyone verify with their "correctly working" system to see if this looks right? The service manual is unclear as to which way the switch is pictured on the car. My switch had the "plugged" port on the far left (standing in front of the car) which showed that my lines were reversed at the switch. Just seems that those lines had been that way since day one and now do not fit well the way they are which is what the manual shows is correct. Now, if the "plugged" port is supposed to be on the far right, that changes everything back to the way it was. Just trying to figure this out!

Picture of service manual diagram & master switch (as it is on my car) attached. 

Thanks!