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1976 Eldorado - hot air inside

Started by LenInLA, October 10, 2016, 05:07:50 AM

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LenInLA

I was driving my 1976 Eldorado today. Nice California day - around 75 degrees. After about 6 miles I felt hot air emanating from under the steering wheel; maybe from the ac ducts as well. The ac is not functioning and is turned off.  Any ideas about the cause? Other than me going through manapause and having hot flushes. Thanks!

Leonard Grayver

"Cadillac Kid" Greg Surfas 15364

Len
From what you said if I were to guess from 6200 miles away (Kyoto Japan), it sounds like you have an open circuit in the sensor string and the programmer is  driven to heat causing the temperature control door to pass all the (natural) air flowing through the system by virtue of the flow through ventilation fan speed or jus high pressure at the cowl intake to be heated and flow out the heater (lower) outlet.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

TJ Hopland

My 73 would do that too.  For mine putting the mode lever to vent/econ and the dial to 65 was the way to get the least amount of hot air coming in.  There was still a little but that could have just been from the engine coming over the cowl.   Was a huge improvement over actually getting heat off the heater core.

There is a lot to these systems and a lot to go wrong at this age.   Its a whole chain different systems to make things happen.   Starts out as resistance of sensors or the dial that gets converted to voltage that gets converted into vacuum that operates the transducer which is what operates the fan speeds and runs the air doors via vacuum motors.   Its pretty simple and complicated all at the same time.         
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

35-709

#3
When switched to OFF the blower motor still runs on low speed AND the vacuum operated water valve is open allowing hot water to pass through the heater core, basically giving you constant heat on low blow even when the system is off.  Putting the mode switch in VENT, as TJ mentioned, closes the water valve.  The blower will still run on low speed but there will be no hot water running through the heater core.  The blower motor runs any time the ignition is switched on, presumably to keep the duct work dry to help prevent fogging of the inside of the windshield.

I have seen, on occasion, where someone has put a manual switch in the blower motor 12+ line and mounted it in the dash to turn the blower motor off completely, not something I would do.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

STS05lg

Len, had the same thing happen on my 75. It was the programmer, that is behind the glove box. Eventually the system will default to high heat even with the system off. Scot Minesinger my chime in, he was able to completely repair my system after much effort. It had to be repaired because the whole system went down on my way back come a show in Wilmington and it was no fun driving the car 100 miles with the heat going full blast in June. Lynn

7gen

I'll put in a plug for CadillacTim's Climate Control Manual, which has a very good troubleshooting section along with a detailed description of exactly what is happening when you move that lever.

Caddyjack

Quote from: 35-709 on October 10, 2016, 10:06:25 AMPutting the mode switch in VENT, as TJ mentioned, closes the water valve. 
As an owner of a '76 Eldo, I can tell you there is no "VENT" setting. Only "OFF", ECONOMY, AUTO (lo and hi), BI-LEVEL, and DEF.
Jack Larson
Philadelphia, PA

cadillacmike68

Quote from: Caddyjack on October 11, 2016, 09:45:47 PM
As an owner of a '76 Eldo, I can tell you there is no "VENT" setting. Only "OFF", ECONOMY, AUTO (lo and hi), BI-LEVEL, and DEF.

In that case, "Economy" would the setting to use. The difference between "Vent" and "Economy" is:

Vent - non- heated, non-cooled air comes out the dash vents at fixed low blower speed. I believe the last year this was used was either 1970 or 1972.

Economy - system will attempt to maintain the dial's set temp WITHOUT turning on the compressor. This started in 1971 or 73 (or possibly later, but definitely by 1975)

Regards,
"Cadillac" Mike

35-709

Right, thank you for clarifying, use "Economy".
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

TJ Hopland

That was why I said vent/econ.   I knew it changed names at some point but was not sure when. 

I wonder if there was a measurable difference in the fuel economy using this mode?   Maybe in a lab but I sure would not think you would notice in regular driving.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

cadillacmike68

Big difference TJ, Compressor does not operate in Vent or Economy.

I was just in a 72 and it goes Off Vent Lo Auto Hi BiLevel Def

1973 or 74 (or perhaps as late as 75-77) must have been the first use of "economy", which actually tried to modulate the temp - without the compressor. It would work pretty good this time of year in the snow belt and obviously during the winter, but if its raining or snowing, you need it on one of the last 5 auto type settings to run the compressor to de-humidify the incoming air!
Regards,
"Cadillac" Mike

The Tassie Devil(le)

On my '72, I can modulate the temperature coming out the vent by turning the heat control.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

Scot Minesinger

It could be anything, and your best bet is to go thru it.  Buy Tim's book as that saves much time flipping thru shop manual and has a better user format.  Plus Tim's book has some info not in the shop manual.  Each book is specific to the year.  I bought all of them 64 thru 76.

Anyway, could be:

1.  bad vacuum hose on control valve making it stuck open
2.  bad control valve
3.  bad programmer (the transducer fails)
4.  interruption to sensor string as Greg suggested
5.  vacuum hose leak in system somewhere or in likely in multiple locations.

You can start with putting a known full vacuum hose (like of intake manifold) on valve to be sure it closes.  That way you know the valve if heat stops.  Then measure vacuum going to valve from controller to make sure you have full vacuum, probably not if valve is good.  If not then check to make sure vacuum hose is good and vacuum is applied to controller/programmer.  If hose is good, and vacuum is going to controller/programmer... you get the idea.  This procedure I just wrote is a half hour easy work for the unfamiliar, ten minutes for experienced people.

Good luck
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

TJ Hopland

Was there ever both vent and economy?   I was thinking they just renamed it, my guess was after the gas crunch of 73 so it would have been on 74 or later models.

Quote from: cadillacmike68 on October 17, 2016, 01:15:09 AMBig difference TJ, Compressor does not operate in Vent or Economy.

Big difference?  Like how big?   My experience is the compressor load hardly made a difference on cars half the size and half the horsepower.    Maybe a bigger gain than the leaning hood ornament we are joking about in another thread but I'm thinking its got to be pretty minor.     
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

35-709

About 2 miles per gallon difference with AC off in both my 472 powered '35 and my '73 Caribou --- both running A6 compressors.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

TJ Hopland

Interesting,  so that is like 11 vs 13?
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

35-709

 ;D  Something like that.  The '35 gets slightly better mileage overall because of the 700R4 transmission (might do better yet if the car wasn't such a square box)  but the difference between AC on or off is still the same.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2