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A/C wiring under the hood for the compressor
#1
All,
I recently bought a stock A/C System off one of the members here. The question I have is where the Compressor black wire hooks to under the hood. I see on the back of my engine, two wires with the same weird looking plastic connectors. One is Red and One is black. The Black wire hooks to another black wire that has the same funny looking plastic connector. I have never seen connections like it. It reminds me of a fiber optic connection. The Red one has 12 vdc on it at all times. The black one has no power at all. The air conditioning has not been charged yet if that matters. I believe it does. The setup is a 71 Mach 1 with the 351 Cleveland engine. I am going to change out the heater and A/C assembly and blower assembly this afternoon. I also will probably need to determine where the two vacuum lines come through the bulkhead connector also. The gentleman I bought it from does not remember how the black wire was hooked up.
Thanks in advance.
Kerry in Virginia Beach.
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#2
At the top of the page one of the sections is 'Data'. Under there you will find the wiring diagrams that should help.

Here is the one for a 71

http://www.7173mustangs.com/images/1971_full.pdf

The A/C clutch solenoid is operated from input from the controls. There is only one wire to the compressor. Basically the way the AC system works is:

With the ignition in the 'on' position power is supplied to the fan switch.
If the fan switch is in any position other than off then power is supplied to a switch that is controlled by the selection of 'max' or 'fresh' controls. In any other position (off, defrost, heat, etc) this switch is 'off'.
When it is on, it then goes to a temp probe to make sure the evaporator hasn't frozen. From there it goes to the compressor.

(This is from memory)

So, with the ignition on (even if the car is not running, the fan in any position other than off and the selector on 'max' or 'fresh' you should be able to see 12v at the compressor connector.

Hope this helps!

'Mike'
73 Convertible - 351C/4V CC heads/4bolt/forged flat tops/comp 270/rhodes/mallory unilite/tri-power/hookers/glasspacks/c6/3.50 limited slip/Gear Vendors/Global West sub frames, strut rods and shelby style traction bars/ Rear sway bar/tilt steering (not original)

Pics of modifications included in:
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#3
Wootdog;249978 Wrote:All,
I recently bought a stock A/C System off one of the members here. The question I have is where the Compressor black wire hooks to under the hood. I see on the back of my engine, two wires with the same weird looking plastic connectors. One is Red and One is black. The Black wire hooks to another black wire that has the same funny looking plastic connector. I have never seen connections like it. It reminds me of a fiber optic connection. The Red one has 12 vdc on it at all times. The black one has no power at all. The air conditioning has not been charged yet if that matters. I believe it does. The setup is a 71 Mach 1 with the 351 Cleveland engine. I am going to change out the heater and A/C assembly and blower assembly this afternoon. I also will probably need to determine where the two vacuum lines come through the bulkhead connector also. The gentleman I bought it from does not remember how the black wire was hooked up.
Thanks in advance.
Kerry in Virginia Beach.
Kerry,
Was your car air originally? Are you going to have to cut the holes in firewall for the air unit? You also have to do drain hole in the floor before install. I have a template somewhere for the hole for air and you have to plug the old heater hose holes.
The pics with air are a 73, note drain hose shown on inside photo and one without is a 72. The air car is not here or I would check the harness.
Not certain if all under dash harnesses have provisions for air or not same under the hood. Will be good to know.
David


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When a man is in the woods and talks and no women are there is he still wrong??
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David
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#4
will e;249980 Wrote:At the top of the page one of the sections is 'Data'. Under there you will find the wiring diagrams that should help.

Here is the one for a 71

http://www.7173mustangs.com/images/1971_full.pdf

The A/C clutch solenoid is operated from input from the controls. There is only one wire to the compressor. Basically the way the AC system works is:

With the ignition in the 'on' position power is supplied to the fan switch.
If the fan switch is in any position other than off then power is supplied to a switch that is controlled by the selection of 'max' or 'fresh' controls. In any other position (off, defrost, heat, etc) this switch is 'off'.
When it is on, it then goes to a temp probe to make sure the evaporator hasn't frozen. From there it goes to the compressor.

(This is from memory)

So, with the ignition on (even if the car is not running, the fan in any position other than off and the selector on 'max' or 'fresh' you should be able to see 12v at the compressor connector.

Hope this helps!

Just to add there is also a solenoid at the throttle linkage that will energize when AC is on to increase engine RPM to compensate for the increased engine load with the compressor on.

-john
(jbojo)
351C 4V cc heads, 10.5 : 1 CR, 290 Herbert cam, Flat top forged pistons, forged connecting rods, Atomic efi,
C6 with Gear Vendor overdrive, 3.89 Tru Trac, Hooker Super Comp with 2 1/2" Pypes Exhaust.        

Some Mod pictures can be seen at:

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#5
The carb idle up solenoid on AC cars remains energized all time when the key is in start or run position, it does not turn on and off when the AC is turned on or off. The only time it shuts down is when the engine is shutdown to prevent dieseling.

On a modern car the idle kicks up or down with the AC being on or off.

I'm not sure why ford did it that way on the AC cars with the idle up solenoid, it seems to compensate for issues with the original oem carb. It would make sense to just have it kick on when the AC is used to compensate for load of the compressor, but ford just made it compensate for accessory loaded cars in general, and then prevent dieseling on shutdown. Ford does refers to it as the anti dieseling solenoid in the factory parts book.

At any rate that connector for the solenoid makes for a perfect electric choke connection on aftermarket carbs.
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#6
72HCODE;250051 Wrote:The carb idle up solenoid on AC cars remains energized all time when the key is in start or run position, it does not turn on and off when the AC is turned on or off. The only time it shuts down is when the engine is shutdown to prevent dieseling.

On a modern car the idle kicks up or down with the AC being on or off.

I'm not sure why ford did it that way on the AC cars with the idle up solenoid, it seems to compensate for issues with the original oem carb. It would make sense to just have it kick on when the AC is used to compensate for load of the compressor, but ford just made it compensate for accessory loaded cars in general, and then prevent dieseling on shutdown. Ford does refers to it as the anti dieseling solenoid in the factory parts book.

At any rate that connector for the solenoid makes for a perfect electric choke connection on aftermarket carbs.

Thx I should have known that. I was researching this the other day and I forgot that the purpose was to ensure that the throttle blades closed more to prevent the dieseling.

-john
(jbojo)
351C 4V cc heads, 10.5 : 1 CR, 290 Herbert cam, Flat top forged pistons, forged connecting rods, Atomic efi,
C6 with Gear Vendor overdrive, 3.89 Tru Trac, Hooker Super Comp with 2 1/2" Pypes Exhaust.        

Some Mod pictures can be seen at:

  Reply
#7
Regarding the wire colors and the connectors: the connectors should be bullet connectors, but with much larger moldings than normal.

For 1971, A/C lines were optional; as far as I can tell, all 72 and 73 Mustangs received AC wiring whether the car had AC or not.

From the headlight harness, a large section of wiring breaks out past the firewall that includes the engine gauge feed plug, the wiper plug, NSS/BU plug, and a number of single large female bullets. The black female bullet with a brown wire is for the PRNDL lamp system. A white female bullet with a red/yellow wire goes to the carb solenoid. A green female bullet with brown/yellow wire is for the AC clutch.

Let me check your shorts!
http://midlifeharness.com

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#8
All,
All I see is a Red and a Black wire together. The other three are on a 3 plug connector. I have those for temp gauge, oil gauge, and I believe distributor. (I have not looked at these In a while). As far as the A/C goes, this car at one time prior to my owning it had A/C. I ended up leaving the original heater slash A/C assembly and blower in it. Now I need to find some O rings for the lines. Then I will see it if will hold a charge. I have a friend that does A/C charging.
Thanks,
Kerry
  Reply
#9
Woot, some pics might help. It's great that your car had AC originally.

On a side note, I am impressed by the forum response. What a great group! We will support Woot though this!

'Mike'
73 Convertible - 351C/4V CC heads/4bolt/forged flat tops/comp 270/rhodes/mallory unilite/tri-power/hookers/glasspacks/c6/3.50 limited slip/Gear Vendors/Global West sub frames, strut rods and shelby style traction bars/ Rear sway bar/tilt steering (not original)

Pics of modifications included in:
  Reply
#10
Sorry guys for not updating sooner. I went back to work after the holidays and have not messed with it anymore. It only has two wires at the back of the engine one has power, the other does not. I will see if I can get a pic tomorrow before it gets dark. they are funny looking plugs. I have put in new Orings and hooked all the lines back up. If I stay with R12, I should not have to replace the drier correct?
Kerry
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