C4 Airconditioning

WA Vetter

Member
Joined
Jun 1, 2009
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5
Location
Perth Australia
A post from a newbie

Can anyone tell me why the connector that joins the air cond compressor to the wiring harness has a diode in it - what does it do and where can I get a new plug (part number if possible) mines missing - Its an 1988 Vette with climate control.
 
smoother clutch release, without it the clutch could potentially chatter. When disengaging the clutch the mag field in the windings (coil) collapses and creates another voltage spike (think ignition coil) which could re-engage the clutch. Hence diode, a 1 way valve.
 
smoother clutch release, without it the clutch could potentially chatter. When disengaging the clutch the mag field in the windings (coil) collapses and creates another voltage spike (think ignition coil) which could re-engage the clutch. Hence diode, a 1 way valve.

Close, but no bananna TT.....it is there because the computer controls the clutch application, OR it is in parallel with the device that does....because the engine computer needs to know the a/c is demanded/compressor on....

what happens is that spike you are correct about happening will damage any solid state output devices driving the request signal, OR input to the computer on that end.....so the guys killed that spike at the compressor instead of any other elsewhere, like at the computer input or a/c controller.....keeps the wire lines clean....

same diode we used in the transmit circuit for pulse field metal detectors 30 years ago, and is used for damping the yoke/flyback pulses in old CRT TV sets.....

:twitch::smash:
 
The diode is there also on earlier models without a computer....whaddaboudad? 68427 please chime in!!! The clutch is also not computer controlled on anything OBD!, I think that only came w/ OBDII It's a simple circuit controlled by your hvac control and the various pressure swithes (depending on year there may be 1 up to 3)
 
The diode is there also on earlier models without a computer....whaddaboudad? 68427 please chime in!!! The clutch is also not computer controlled on anything OBD!, I think that only came w/ OBDII It's a simple circuit controlled by your hvac control and the various pressure swithes (depending on year there may be 1 up to 3)

Yes, but the comp switch on my custom console also feeds the computer, telling it the compressor is running, increase idle....and turn on fans.....

that input would be screwed without that diode.....my speed density comp is wired like a '91 F body....

:thumbs:
 
Yes, fan request and idle bump, but that's not the ECM controlling the compressor clutch, there is no control what so ever. The ECM doesn't even sense directly off the clutch, the compressor relay is in between

Fig57_1991_body_wiring_continued.gif
 
I thought the ecm only uses a pressure sensor on the a/c lines to detect a/c on/off to run fans and change idle.
 
Can't help you on a part number, but a electronics house will have a ordinary power diode.....say 2 amps and 1000 PIV rating....that's all I used on my clutch 15 years ago for the initial install on my '72.....

the striped end goes to the wire, the other end goes to ground....

:thumbs:
 
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