What does this diode on the AC compressor do?

While taking my engine apart I noticed that this diode wasn't connected properly:

<a href="http://picasaweb.google.com/martin.edelius/BuickGS1972/photo#5043186079210431314"><img src="http://lh5.google.com/image/martin.edelius/Rfz_BOOIY1I/AAAAAAAAAXI/li7yf-KGrMk/s288/PICT0016.JPG" /></a>

I have no idea why it's there as the connector just seems to ground the housing of the AC compressor.

Here's a bigger shot of the wires/diode:

<a href="http://picasaweb.google.com/martin.edelius/BuickGS1972/photo#5043192856668824658"><img src="http://lh4.google.com/image/martin.edelius/Rf0FLuOIZFI/AAAAAAAAAYY/pMmxOKC-woI/s288/PICT0014.JPG" /></a>

Any ideas?

TIA.

 

Is that a capacitor? Does it say it is rated in micofarads? (mfd)

 

If it is diode I suppose they are using it as a half wave rectifier to futher refine the job being done by the bridge rectifier in the alternator. If it is a capacitor it is intended to lower the current needed to start the compressor by adding reactance to a circuit dominated by an inductance. This is often done on power grids, AC compressors for your home etc.

 

It is a Diode, it is suppose to be between the 2 leads.
it is suppose to help disengage the clutch and eliminate voltage spike when the clutch is disengaged.

 

Thanks Larry - I'll reconnect it then.

 

A diaode only lets electricty flow in one direction. :Smarty:

It does not have to be there for the compressior to work, but lets the clutch to engege and release smoother.

 

For you electrical engineers out there- the diode is used to prevent the clutch from chattering on disengagement. You may recall that if a voltage is applied to a coil, the clutch coil, it creates a magnetic field, pulling in the clutch. On disengagement, the collapsing magnetic field will create what is called a counter voltage, which may be strong enough to re-engage the clutch. The diode, which is reverse biased, or installed backwards, creating a short to the counter voltage created by the collapsing magnetic field. This prevents the chatter as the clutch disengages. Ray

 

You will find a similar one on the engine harness,on pass. side of the carb.. Used for the TCS, factory installed.

 

larrys right stops (lol) power form spiking back in the elec system

 

As an electrical engineer, do I get to score everyones answers ?? LOL.

 

Haha, go right ahead.

 

Martin, that compressor electrical connection should face outside towards the passenger fender. Now the connection is too close to the alternator and wires could get caught in belt. You are kind of limited with the MSD the way it is mounted.

 

No worries, it's all coming off in the resto:

<a href="http://picasaweb.google.com/martin.edelius/BuickGS1972/photo#5045522576587240194"><img src="http://lh5.google.com/image/martin.edelius/RgVMDROyMwI/AAAAAAAAAgM/DPj5742ZpS4/s288/PICT0002.JPG" /></a>

 

Good, bad place for an MSD

 

Yeah, it's not optimal in any way.

I'm following the thread about MSD box placement and I think I know where to put mine.