pnhigg

iTrader: (3)

I have a 92 fullsize chevy truck with a 5.3/t56 combo.
I have been running a Mark VIII single electric fan on a rocker switch for about a year while finishing up some other bugs.
I decided this weekend that I would wire the truck to operate the fan on the pcm signal.

My plan was to use the high speed fan signal to signal the fan to come on.
I used a 75 am relay, and connected a 10 ga wire from the battery to pole 30on the relay.
87 was 10ga to fan.
86 ignition on 12 v
85 pcm to pin #33 red connector

When the truck reaches temperature the fan signal from the pcm is pulsing(best I can describe).
The relay works when grounded apart from the pcm, but when the relay is connected to the pcm it is clicking on/off every half second or so.
I initially thought maybe I was at the threshold of when the ect was high enough to kick on the fans, but I let the temp rise to 210 and still only, on/off every 1/2 second.

Any ideas?

Thanks in advance.

busta9876

iTrader: (3)

What calibration programmed into PCM? I am assuming F-Body. Any reason not using the low speed fan turn on? Blue - 42

Would need to make sure settings in PCM set correct. Not sure what would happen if th Fan on/off temp was set the same. Usually they are programmed to turn on, and let temp drop 3-4 degrees then turn off. If they are set same maybe that is what is happening.

Low speed fan relay control should GROUND first at one programmed TEMP, and then if temp raises to a second programmed TEMP the high speed fan relay control will ground. Both LOW and HIGH temp setpoints can be changed.

Speartech

iTrader: (14)

When using a truck PCM calibration you have to use the primary fan hookup, not the secondary. Switch that over to Blue 42 and you'll be fine. What you are calling low speed and high speed has nothing to do with the actual speed of the fan. That's why I still call them primary and secondary fans. Your fan will work perfect triggering from the Blue 42 position.

pnhigg

iTrader: (3)

Thanks a ton for the help guys.
Fan is working well using blue #42.

Next question involves the fans coming on when the a/c clutch is engaged.
It looks like when red #17 receives 12volts the idle should speed up and the fan kick on.
Obviously that is not the way it works because I am not getting anything when I send 12 volts to red #17.

I am using the original 92 a/c setup (converted to r134A).
Everything compressor wise works using the low pressure switch on the accumulator, and it cools very well.
The trouble is, how do I let the pcm know the a/c is on so the fan will come on and the idle will step up.

My current hptuner file has the idle increasing 100rpm when the a/c is on, but nothing is happening.

Thanks again for the help and the patience.

Speartech

iTrader: (14)

You can either reflash it with an F-body file to make all of that work, or you can just add a freon high pressure switch to the fan circuit. That works great. The idle bump isn't really a big deal. Without it, the system is re-active instead of pro-active. The A/C comes on and drags the idle down a little, the PCM reacts and idles up to compensate.