Diode on air compressor, what's it do

[bigsteve1635]

Hi ALL

I have just brought a new compressor fom the USA for my 3.3 grand voyager 1996 with dual air con, the system worked was fine but the compressor was noisy, so ordered a new one via e-bay as they are less than half price in the US. It arrived no problem, but my old compressor has a doide on it but new one does not, what does the diode do ?, can I run without it ?, can I reuse the old new on the new compressor. HELP

regards

Steve F

[dbfordtech]

hey big steve,
The diode is there because the a/c compressor clutch is an electromagnetic
clutch (I'm sure you know this already) when any electromagnet is turned
off (like when your a/c cycles) the collapse of the magnetic field induces
a secondary voltage that can be very very high. Infact your ignition coil relies on this principle to generate high voltage for your plugs. But you dont
want it at your a/c compressor. The diode disipates this voltage.
If you look at alot of quality automotive relays, you will also find a diode symbol, or a resistor symbol, they are there for the same reason.

[bigsteve1635]

Many thanks

I found a diode in line under the insulation tape a very small one, its not like old one which was wired like a resitor between - and + and was quite large.
Thanks for the info.

Regards

Steve F

[gbic1]

Diodes allow voltage to flow one way and not the other. If it flows backward it can cause a voltage spike which would blow the ecm.