Value of compressor clutch flyback diode

[dmjlambert]

Does anybody know the part number of the air conditioner compressor clutch flyback diode? It should have a number, probably starting with 1N. The markings on mine are worn off with age. The purpose of the diode is to reduce arcing in the compressor switch contacts and therefore extend the life of the switch.

[Andy4639]

This is on E bay. Looks close to factory but it says 1982 -96.Message Vvett he should be able to tell you.


https://www.ebay.com/i/274086621531?...kcid=28&chn=ps

[RustyPile]

The collapsing field of the clutch winding when the power is removed can get pretty strong, producing a pretty good voltage spike, referred to as Peak Inverse Voltage, or PIV for short.. I've never measured that spike but it probably exceeds 100 volts.. A 1N4004 is a 1 amp 600 PIV diode.. A 1N5402 is a 3 amp 200 PIV diode.. A 1N4007 is a 2.5 amp 1000 PIV diode.. A 1N5408 is a 3 amp 1000 PIV diode.. Any one of these diodes will work just fine....

[Andy4639]

I checked all 3 of my owner manuals and none of them list it are even mention it except one and it calls it a rectifier, not diode. But it didn't give any info on it.
I'd ask some friends who are running the A-6 compressor on their vehicle to see what size it is.

[Steeveedee]

A diode will allow current to flow only one way (with a miniscule amount of leak).

A rectifier turns AC into DC, so they are not the same.

[dmjlambert]

A rectifier is a diode that is used to convert AC to DC. Rectifier indicates the function it is doing more than the device used to do the job. The rectifier diode allows electricity to flow just one direction, essentially interrupting the AC, which wants to flow both ways in a circuit, thus making DC.

If you use that same diode wired across the clutch terminals or across relay winding terminals, it's function is a clamp or spike suppressor.

[Andy4639]

Well the 71 shop manual call's it a rectifier in the schematic. I only post what it says, I can't say weather it's right are wrong.
You will have to decide that for your self.

[dmjlambert]

I don't think I would call it wrong, but it's not the word I would have chosen. Perhaps it is the best word from an automotive engineering view, not necessarily from an electronics point of view. Whether they call it a rectifier or diode, those are the same thing and the diagram still does not indicate the orientation of the cathode side of the device. That is an omission or error in the diagram. It would be nice if somebody with a very good condition original diode on their truck could read the numbers off of it for me. I just like to know these things.

[CG]

I need a magnifying glass to read mine (which I dont have), but it does have the Motorola symbol and it looks almost like a 1 N. My old eyes even with my glasses cant quite bring it all the way in.

[dmjlambert]

When I am faced with that circumstance, I take a picture with my iPhone and then zoom in on the picture to read stuff like that. It usually works better to have plenty of light but not use the flash in the camera because flash sometimes causes glare.

[CG]

Thats how I tried to do it. Ill post the two pics I have, give me a second ....

[Andy4639]

Originally Posted by dmjlambert

I don't think I would call it wrong, but it's not the word I would have chosen. Perhaps it is the best word from an automotive engineering view, not necessarily from an electronics point of view. Whether they call it a rectifier or diode, those are the same thing and the diagram still does not indicate the orientation of the cathode side of the device. That is an omission or error in the diagram. It would be nice if somebody with a very good condition original diode on their truck could read the numbers off of it for me. I just like to know these things.

I went out and looked at my 64 SS Impala with the A-6 compressor and it doesn't have it. It has spade connectors on it. I may order this one for it though. You got me thinking. The band on a diode always goes toward the positive side always.

https://www.repairconnector.com/prod...ith-Diode.html

https://www.compressorworks.com/Uplo...STALLATION.PDF

[dmjlambert]

Originally Posted by CG

Thats how I tried to do it. Ill post the two pics I have, give me a second ....

Thanks. You have the M for Motorola, below that you have 1N and the rest of the number is probably below the 1N and not visible in the picture.

[CG]

I tried but couldnt get it to come in to focus. If you havent figured it out by tomorrow Ill try to scrounge up a magnifying glass.

[dmjlambert]

Thanks!

[HO455]

Originally Posted by RustyPile

The collapsing field of the clutch winding when the power is removed can get pretty strong, producing a pretty good voltage spike, referred to as Peak Inverse Voltage, or PIV for short.. I've never measured that spike but it probably exceeds 100 volts.. A 1N4004 is a 1 amp 600 PIV diode.. A 1N5402 is a 3 amp 200 PIV diode.. A 1N4007 is a 2.5 amp 1000 PIV diode.. A 1N5408 is a 3 amp 1000 PIV diode.. Any one of these diodes will work just fine....

RustyPile has posted good information. The function of the diode doesn't require it to be a specific value. I would bet that GM installed the diode to prevent warranty issues, so cost and not specifications decided which one they used. It is likely the diode installed in the harnesses changed over the years due to cost reasons.
You could try contacting one of the aftermarket wiring harness manufacturers for their recommendation if you want more specific information

[kwmech]

My thought with the diode was so you could shut the engine off with the AC on, otherwise the magnet would create power to keep the engine running

[VetteVet]

If you guys recall, the relays for the cooling fan and several others have the diode to dissipate the coil induced voltage when the relay is shut off. This voltage is sent to ground to prevent damage to the relay points and to prevent feed back current to the positive side of the relay coil.

My thought with the diode was so you could shut the engine off with the AC on, otherwise the magnet would create power to keep the engine running

How would you explain the ones without the diode? Once you kill the engine you shut off the electromagnet which de-energizes the clutch.

[dmjlambert]

Originally Posted by CG

I tried but couldnt get it to come in to focus. If you havent figured it out by tomorrow Ill try to scrounge up a magnifying glass.

Hi CG, if you have an opportunity to take a zoomed in picture of the other side of the diode to get the part number that follows the 1N that would be great. I know RustyPile gave a list of diodes that may be OK to use, but I would also like to know what the Chevy engineers designed.

[Sheepdip]

Here's the one I bought (the whole pigtail) and installed...works like it's supposed to.

https://www.ebay.com/itm/GM-R4-LTR4-...l/283422620623

['68OrangeSunshine]

Shoot me if I'm wrong -- I took Basic Electricity & Electronics at NAS Memphis 47 years ago -- but the silver stripe indicates the Positive side of the Diode's polarity.


--Strike That -- dmjlambert says it's the Negative.
I Stand Corrected.

[dmjlambert]

The stripe is the cathode, which is negative side. But it depends how you look at it. For a flyback diode wiring configuration, we are going to put the negative side of the diode on the positive power supply going to the solenoid, relay coil, or clutch. The anode or positive side of the diode is connected to ground. It won't conduct electricity until the switch is opened and the magnetic field of the coil collapses. Then it will conduct to discharge the coil and prevent an arc across the opened switch contacts. Here's a good article about it. https://www.electronicshub.org/flyba...heeling-diode/

[CG]

Its pretty messed up but it looks like 400, cant read anything else.

[dmjlambert]

Thanks for checking, I really appreciate it. It would have 1 more digit, such as 1N4001, 1N4002, 1N4003, etc. It could be somebody else has one that is in better shape and can post here what the value is, for the sake of my curiosity. I have a friend who has a 1972 truck with big block and factory air conditioner and he's not a member here, he doesn't do the computer thing. I'll have a look at his truck tomorrow and perhaps it has the diode and is readable. I was just looking at his truck today and forgot to look at that.

[BigBird05]

On page 1A-41 of the 72 service manual It is called a Diode with the Stripe on the + green wire. In the same book page 1A-43 it is called a rectifier. These books are written by tech writers, then proof read by the engineers. No value is given. I'll bet it is a non serviceable part. You are on your own finding the value.