substitute relay for a/c

Porsche (mine's a '96) uses a relay for the a/c condenser that looks like this part number 964-615-215-00: (sorry for borrowing and modifying the12volt.com's graphics) It appears similar to the SPDT Relay discussed on the relay page except the center terminal is numbered 31 and is grounded. It is stamped with 12V 10A. This relay costs ~$50. I'd like to substitute this relay part number 141-951-253-b: This has no center terminal at all. It's marked 12V 40A. It only costs ~$5. So you can see why I'd like to use this as a substitute. Any of you expert auto electricians have thoughts about making this swap? Thanks, JC

You can get five pin relays for $5-10.  I would use a relay that has the same amount of pins as the stock relay.Kevin Pierson

Kevin, Thanks for the reply. Any tips on how to back into a part number for a 5 pin relay? Or a website or other source that lists relays in such a way I can search one out?

If the pin layout is like the one you posted above then that is a standard bosch style relay.  If the pin layout isn't like above you may need to go to a car parts store and see if they could cross reference it for you.Kevin Pierson

The pin layout is exactly like posted above. The challenge I've had is finding a relay that is designed with the center pin numbered 31. All the 5 pin relays I've seen number the center pin 87a.

Another thought. I wonder if this is actually a SPST Relay with the center pin (87a on a SPDT) numbered 30 and grounded.

I mis spoke on my last posting. The grounded pin is numbered 31. Here's a drawing of the schematic from the relay I'm trying to replace:

It looks like a reverse voltage breakdown diode.  That is an odd relay you got there!Kevin Pierson

KPierson wrote: It looks like a reverse voltage breakdown diode.  That is an odd relay you got there!

Guess that's why it costs 50 bucks! So how about my suggested substitution?