Heater fan

XR4Ti / Sierra / Sierra Cosworth Discussions - Questions, problem resolution, general talk, technical tips and modifications.
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Heater fan

Post by Captainw1990 » Mon Mar 01, 2010 7:55 pm

Hey guys I have an 88 turbo coupe engine with the la2 computer in my Ranger. I am trying to set up a relay for my radiator fan. I was wondering if pin 52 (primary fan) was just a ground. Meaning it would go to ground when the fan was supposed to turn on. I have it set up as if that is true but the fan is not kicking on. I tested it by grounding it with a wire to the neg side of the battery and the fan worked so I know the rest of the circuit is good. If anyone would be able to help me I would appreciate it.

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Post by DPDISXR4Ti » Mon Mar 01, 2010 10:37 pm

The primary fan circuit with the LA class of PCM's ('87/8 TC) is an inverted circuit - i.e. Closed = off, Open = on.

If you don't use the factory relay box from the TC, you can use two relays to accomplish the same thing. It's a bit convuluted, but it can (and has) been done. The seconday fan circuit is a "normal" one, but it comes on a little late to be used as the primary.

Most people don't bother with this capability when using these PCM's in a non-original application like a Ranger or Merkur.

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