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1976 CDV Under Hood Wiring Question

Started by Chas, January 18, 2018, 12:10:43 PM

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Chas

My winter project is detailing the engine of my low mileage Coupe. I have found a wire in my factory harness that is not connected to ANYTHING! Searched through the manual, along with any schematic I could find. Nothing! I'm not a guy who likes "loose ends" so was hoping someone could tell me what this wire is for.

Location: The flexible black plastic loom that lays on the intake manifold, next to the valve cover on the right side (passenger side) of the motor. About half way down this loom, it makes a "T". At the base of this "T", there is a hole drilled into the fitting where the wire(s) for the choke come out. There is also a tan wire that ends in a round, black rubber "hat" fitting exiting this same hole. This is the wire in question!! Would appreciate knowing what it is for!!

Engine is obviously a 500 c.i. and with carb, not fuel injected. No air pump. Can't check wire for voltage since battery, alternator, starter, etc... are currently out of the car. Thanks in advance!
1967 Coupe DeVille
1970 Coupe DeVille
1976 Coupe DeVille
1983 Coupe DeVille
1977 Harley Cafe Racer
1991 Harley Fat Boy
1957 Harley Hardtail
1949 Lusse Bumper Car
If you're 25 years old and not a liberal, you have no heart. If you're 45 years old and not a conservative, you have no money!

"Cadillac Kid" Greg Surfas 15364

Chas If I were to guess I would think that would be the wire/connection for the AC compressor super heat switch.  Shoukd extend to and connect at the rear of the compressor.
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

How about the temp switch in the corner of the head behind the alternator? 

I thought most of the AC stuff came down the other side but I could be remembering wrong.
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

"Cadillac Kid" Greg Surfas 15364

TJ,
How can you possibly think you are wrong?  You are wrong. AC thermal switch leads are in the loom on the passenger side of the motor.
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-

Chas

Problem solved...with the help of Greg's advice! The temp switch in the front of the right head is wired up. HOWEVER, even though this is an original 20,000 mile car, the AC compressor has been replaced. How do I know? There's a big fat NAPA sticker on it instead of the Frigidare decal! This compressor DOES NOT have a superheat switch mounted in the rear of it. Seems that whoever installed this compressor, they just coiled up the tan wire and left it on top of the intake manifold. Additionally, on the front of the compressor, the wiring plug to engage the clutch is mounted at the 2 o'clock position, whereas the correct compressor has them at 10 o'clock. Imagine that.....a parts counterman supplying the wrong part.....never seen that happen before!!!........LOLOL!!!!!
1967 Coupe DeVille
1970 Coupe DeVille
1976 Coupe DeVille
1983 Coupe DeVille
1977 Harley Cafe Racer
1991 Harley Fat Boy
1957 Harley Hardtail
1949 Lusse Bumper Car
If you're 25 years old and not a liberal, you have no heart. If you're 45 years old and not a conservative, you have no money!

"Cadillac Kid" Greg Surfas 15364

Chas,
The super-heat switch location on your replacement compressor most likely  (unless it is a pre-1970 core) came with a plug instead of the switch.  The intent is that the plug be removed and the super-heat switch (if the original compressor had one) is removed from the original and installed with new o-rings in the replacement. The "rationale" being that this compressor (the A-6) fits a multitude of applications over a multitude of years with various options in the switch socket.
It is also possible, the person that changed the compressor just got one off some other car, hence the clutch coil connection clocking.
That however is readily changed by removing the clutch disc, the pulley and all the snap rings to rotate the coil to the correct position.
That said, unless someone has rewired the superheat switch/thermal overload circuit, you might wrap some tape around the end of the wire, since grounding the connection will blow the thermal element thus killing power to the compressor clutch.
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

Now that the problem is solved and we are taking about A6 compressors.......

Did most if not all the A6's have the port for the super heat?   And was it always held with an internal snap ring?  The last one I did was that way but I think it was new 'offshore' production.    A lot of classic vendors seem to list a different compressor w/ and w/o superheat which makes me wonder did late production or repros maybe not include the port?   

If you are dealing with a system that had a super heat switch that is disconnected or not re installed when the compressor was changed you basically have no low pressure protection?  So if/when the system leaks down the compressor just keep trying till something gives? 


Quote from: "Cadillac Kid"  Greg Surfas 15364 on January 19, 2018, 11:20:43 AM
TJ, How can you possibly think you are wrong?  You are wrong. AC thermal switch leads are in the loom on the passenger side of the motor.

I don't get what you mean by the possibly think I'm wrong bit.  I said I could be wrong when I said it and you confirmed it so thank you for confirming I was right to question my memory on this subject.   

I now remember more about the car where it was on the other side and it now makes sense why it was different than other Cads, it was a Miller combo car that had a hard life after it was retired from its original home.  The compressor and kickdown wiring had got tangled up which caused some interesting interactions.  You turn the AC on trans would not shift.  Started to wonder if that was some special feature for funeral processions till we found the melted harness.
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

"Cadillac Kid" Greg Surfas 15364

TJ,the
I thought I was wrong once but then I found out I was mistaken.
Anyhow, In 1970 many manufacturers added the "Thermal limiting" circuit in the compressor feed .  In 1971 Cadillac added it as well.
Prior to those years the rear cylinder head of the A-6 did not have a port for these devices.  Once there were enough of the A-6 cores with the super-heat switch available, just about all the re builders started using the ported cores for their rebuilds.  Once there started to be a shortage of super-heat switches the re-builders gave you the choice of yea or nay and for the nays they just inserted a plug in the port.
The super-heat switch is exactly that.  It is situated in the high pressure side of the compressor and when the temperature is higher than it should be for a given pressure (for an extended period of time) either due to a blocked condenser or no air flow over the condenser,  malfunction of components, an incorrect refrigerant or an shortage of the correct refrigerant the switch "makes", grounding the circuit and blowing the fuse on the thermal element.
Some manufacturers chose to replace the super-heat switch with a high pressure switch and circuitry, but in the A-6 that was short lived.
Short version is that MANY compressors were changed and the super-heat switch was not re-connected thus eliminating the "nuisance" trips (when something was actually wrong) leading up to more compressor failures.
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-

Chas

One last question on this subject and I’ll go away, I promise: the car had been converted to R134 some time in the past. Let’s say that I do install a superheat switch and connect the rogue wire to it. Will that switch be so far out of calibration (due to R134 use vs original R12) that the switch will be basically useless? In other words, should I just leave well enough alone? Should I convert back to R12 and install the switch?
1967 Coupe DeVille
1970 Coupe DeVille
1976 Coupe DeVille
1983 Coupe DeVille
1977 Harley Cafe Racer
1991 Harley Fat Boy
1957 Harley Hardtail
1949 Lusse Bumper Car
If you're 25 years old and not a liberal, you have no heart. If you're 45 years old and not a conservative, you have no money!

"Cadillac Kid" Greg Surfas 15364

Chas
A valid answer depends on exactly what was done to the entire system when R134a replaced the R12

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-

Chas

Greg.....when it comes to A/C systems, you have to talk to me as you would to a small child or a Labrador Retriever. What specifically would you need to know about the entire system?
1967 Coupe DeVille
1970 Coupe DeVille
1976 Coupe DeVille
1983 Coupe DeVille
1977 Harley Cafe Racer
1991 Harley Fat Boy
1957 Harley Hardtail
1949 Lusse Bumper Car
If you're 25 years old and not a liberal, you have no heart. If you're 45 years old and not a conservative, you have no money!

"Cadillac Kid" Greg Surfas 15364

Chas,
When some people change refrigerants they also change the electrical and refrigeration systems.  They eliminate the VIR, they cycle the clutch to maintain temperature control, which essentially defeats the "Automatic Temperature Control" Function.  The short version is that I would recommend going back to a fully original R-12 system what ever is required.
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

Taking and posting some pictures under hood should be enough for people here to make an educated guess what was changed if anything.   

The area of primary interest would be where the AC hoses come and go in the firewall area near the blower.   What the inline canister dodad looks like will give some clues.   The original VIR is a more complex mulit stage assembly.   Many of the conversions are a pretty basic canister with fittings on the top. 

Also get a shot of the modules with wires going into the box in that area.   One of them will be the 'thermal fuse' that is involved with the superheat and clutch functions.   That fuse/module is the most convenient place to tap in for a conversion or where you have to do some bypassing so signs of tampering there would be more signs of a more extensive conversion.   Also where someone would have simply bypassed the fuse that as Greg says was often seen as a nuisance.

And another question Greg can likely answer that I assume I am not the only one curious about.    What is the most likely failure mode we would expect on a system with the superheat no longer working as intended?    Is it just hard on the compressor and will just degrade performance till it can't perform or is there danger of a big bang?   
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

"Cadillac Kid" Greg Surfas 15364

The thermal element (fuse_) circuit is in the compressor circuit for the same reason a fuse or circuit breaker is in an electrical circuit; to let you know something is wrong and to diagnose the problem BEFORE you consider the issue closed.
The super-heat switch  can be triggered by several system discrepancies. Shortage of refrigerant, leaking or broken suction valves in the compressor, restricted condenser circuit, malfunctioning TX Valce or P.O.A., or in extreme cases air (or lack thereof) over the condenser too high for continued operation.
What is the most likely effect of not having the switch/overload fuse inb the circuit? Any of the above problems not noticed until something fails catastrophically.
What is the most common reason for super-heat switch activation? Low refrigerant charge.
The conditions required to activate the switch when it is due to low refrigerant charge are close to the point where there is not enough refrigerant and oil in the system to maintain operation/. No oil in the compressor, compressor go to sleep.
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-