Jumping AC cycling switch but one problem...

dsmithwc04

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Jun 14, 2005
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Okay, I have a 97 cobra and I've already started a new thread but I think I found an issue with my cycling switch. Does anybody else have three wires running into the plug that inserts into the low side switch on the drier? Not only do I have three wires into the plug but the plug has 4 holes and the switch only has 2 pins. How does this work? The 3 wires running into the plug are Red-13.7V, Purple, 5.12V, and Black/white 0v (ground?). The purple 5.12V wire is the hole one of the pins on the switch plugs into. the second of the two pins in the switch plugs into the hole in the plug that has no wire in it. My ac will not cycle when putting 12V onto the purple wire. The AC will turn on if I jump 12V to the blue/yellow wire in the pressure switch near the radiator. I am stumped an so is every freakin shop I take the car to. Please, please, please somebody help me out...
 
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For a stock 97 Cobra (or any Mustang for that matter), the AC low pressures switch has two wires. Input is purple (P). Output is DB/Y. A look at the wiring diagrams shows the switch is open when the pressure is too low.

The low pressure DB/Y wire goes directly to the DB/Y wire on the high pressure switch. You have already confirmed that jumping the DB/Y wire at the high presssure switch causes the AC clutch to engage.

Note, injecting +12 volts to the purple wire at the low pressure switch won't engage the AC clutch because this is going the wrong way. The AC clutch is downstream. The purple wire is upstream.

Further, if the voltage is only 5.1 volts at the low pressure purple wire, this means there's a problem upstream in the AC/Heater control assembly. Refer to diagram 054-002.

Since the wire colors and number of wires do not match, this tells me that either you have the wrong part or there have been some "mods" or repairs done. Perhaps this was someone's attempt to bypass the real problem and inject +12 volts into the system to force the AC to run.

How about some pictures?

Note, regarding the number of pins, I wouldn't worry too much about that. It's common for Ford to re-use connectors and not use all of the pins.
 
Here are some pics. The purple wire was cut by me during testing. I have since reconnected it. The plug looks stock..

Colors are Black/white, Red, Purple

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Also, when I bought the car it the PO had directly wired the plug that supplys power to the compressor with two wires that ran under the passenger side dash to a thermocoupler of some sort that then fed into a connection under where the dash and door meet on the passenger side. I took it all out because it was Kentucky Hillbilly craftsmanship at it's best.

And to confirm, if I supply 12v to the blue/yellow wire on the high pressure switch (near the radiator) it kicks the compressor on. I jumped the purple and no wire pins on the low side cycle switch and nothing happend but again that purple wire has 5v but the red has 13v or so.
 

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The round plug is the low pressure switch. The Red and BK/WH wires are not stock. Need to know where they come from.

The voltage on the purple wire is a problem. Go back to the AC/heater mode controller in the dash and measure there. IMO, you should "know" what you are dealing with before digging too deeply. It's obvious the mods were done for some reason. If you can't get +12 volts out of the mode controller, it won't do much good to restore all of the other mods.

The next problem is what has happened to the DB/Y wire from the low pressure switch. Suggest pulling back the tape and seeing where the "mods" were done. Again, if you can't get a good wire path on the DB/Y wire from the low pressure to the high pressure switch, it still won't work.
 
Okay, peeled back the tape and it appears the wires are definately stock. The connector also has the FORD logo on it so it appears stock as well. It has numbers for all 4 pins and pin 1 is the one with no wire going to it.
 
Can somebody with a 96-96 GT or Cobra post a pic of the connector plug that fits into the ac low side switch near the passenger firewall? How many wires and what their colors are would also help. THANKS!!!!
 
Well, I figured it out. The PO had the wrong plug connected to the switch. The correct switch with Blue/y and purple wires was connected to a vacuum line with a switch on it. I reconnected properly and will test in morning. I'm sure this will solf my problem. However, now I have a new problem. The vacuum line comes from the passenger fender and runs to a switch which then coninues the vacuum line but the line has been pulled off. On a V6 this line runs to the intake manifold. Unfortunately I don't have vacuum diagrams. (wmburns: thought that CD would have the vacuum diagrams or am I missing something?) Thanks.
 
The vacuum line that runs from the passenger fender well is the EVAP vapor line. Just as in the V6 or SOHC GT, it has to go to intake vacuum. It just the details that are different. I don't own a Cobra so I can't give direct help there. Perhaps someone with a Cobra can help.

The vacuum diagrams are in the PC/ED and service manual. They can be difficult to find. Further they are in different places depending upon MY. However, if you are expecting to find a nice picture showing where the EVAP line is connected, it won't be there. What will be there is a general block style flow diagram.

Frankly I suspected that you had the wrong connector. I did a search of the wiring diagrams attempting to identify a connector with matching wire colors, but I didn't spot anything. I'm sure you see now how many connectors there are and just how difficult of a job that is. Without direct proof of what the connector was for, I decided to not say anything and wait for someone else to chime in.

So how did you figgure it out? What is the connector really for? It sounds like progress has been made. How does it feel?

Let me remind you of something. There are several DTC codes that will disable the AC clutch by design. Don't forget this should the AC not work even after the wiring has been restored.
 
I looked under the hood of a known good 98 v6. Saw the blue connector with three wires and it wasn't connector to cycle switch. I then recognized the brown plug with two wires that was and went home and there they were. I'm beginning to find out that I can't trust anything the po did because he was a complete f#@%ING moron. Hopefully my ac will now work and its back to trying to figure out what's wrong with mach 460. Whole nother story there.
 
Finally found what the connector is for.

EVAP purge flow sensor. It's on diagram 024-10. Connector C195. The wire colors are Red, P/W, and BK/W.

Not that it really matters now.

Does the AC work now? Were you able to figgure out where the vacuum line goes?

OBTW, the vacuum diagrams are on cell 140-1 through 140-2 and 054-1.
 
Yes, the AC works now. After weeks of trouble shooting it was a damn connector plugged into the wrong plug... Thanks to all who have helped and especially wmburns. I will check out those diagrams as I've still not found where it plugs into. On the V6 car the part I'm missing went straight into the intake manifold.
 
BTW, one of the codes causing a check engine light had something to do with a charcoal canister for fuel? Well, that EVAP sensor you mentioned has a lot to do with that I'm sure. It is supposted to go to charcoal canister and possibly a solenoid of some sort. I noticed a faint odor of what smelled like fuel vapor in the car and this could be the reason. Now I have to figure out how to fix?
 
Can anybody get me a picture of the vacuum line from the EVAP Purge sensor to the intake manifold? This vacuum line is supposed to allow fuel vapor to enter the intake manifold when the pressure builds up in the fuel tank. Instead of wasting the fuel vapor it allows the engine to burn it. However, since mine is unhooked I am not sure how it routes and where it connects to. This is allowing fuel vapor in the car when the heating/cooling vents are on which is DANGEROUS! I see a vacuum line near the rear on the passenger side but it has a tee which is already plugged into by other various vacuum lines.
 
I no longer have my 96 Mustang. But I remember how everything was hooked up.

The charcoal canister is in the right hand fender well. A vapor line enters the engine bay. Along the firewall, the first active device is the EVAP purge solenoid.

Next in the vapor line is the EVAP purge flow sensor. Note, these break alot and give false readings.

From the purge flow line, the EVAP vapor hose goes the the throttle body vacuum port. I seem to remember on my 96, the EVAP port was to the rear of the TB. Since you have a Cobra, I'm not sure exactly where it goes.

How about some pictures of your engine bay? Pay close attention to anywhere there are capped vacuum lines. Especially the larger 1/4" lines.
 
I know this is an old thread but it helped me with the AC on my 97 gt....PO had the plugs switched the same as on thia thred....also he had a jumper wire ran from the red wire of the wrong plug to a wire on the plug to the compressor....compressor looked burnt up and bearings were toast probably why it was bypassed when I bought it...