327_TPI_77_Maro

iTrader: (8)

I have an 89 305 tpi trans am with dual fans, and now that I got the AC working correctly I notice that the passenger fan kicks in and out correctly when the AC pressure exceeds 235 psi, but the driver's fan, instead of running constantly at idle with the AC on like I thought it would, is also kicking on and off with the passenger's fan. I verified that the fans are both wired correctly and both relays are working correctly, to make sure a previous owner didn't do something wonky with the fan wiring. They are wired correctly. Grounding the passenger's fan relay does not kick on the driver's fan, so the driver's fan cycling is due to its ECM signal...

This thread says that the driver's fan should be on whenever the AC is on

https://www.thirdgen.org/forums/cool...ans-arent.html

However I looked at the ecm wiring, and I looked through the 1989 bin file in tunerpro and that doesn't look to be the case. It looks like the ecm uses a 2nd set of fan on/off temp tables for fan 1 when it receives an AC on signal, and if the compressor high pressure switch kicks on, if the car is below a minimum speed threshold, it will then force the fan on only while the high pressure switch is on. I can't see that there is any provision for fan 1 to run constantly just because the AC is on. But that doesn't seem right, I would except fan 1 to run when the AC is on...why doesn't it, is my question?

I have another 89 and it does the same thing, turning the AC on does not force fan 1 on, and I have verified on that car too that the datalog is showing the AC request signal...

Is it normal for an 89 dual fan trans am to only run both fans at idle when the 235 psi switch kicks on? It seems unusal and annoying for this to be the case but that's what my car is doing.

Reid Fleming

iTrader: (2)

Are both fans turning on/off simultaneously? In other words, they're both spinning down at the same time?

I'm not sure what to say in this regard. I've watched mine in action while standing in the driveway with the A/C on. And the driver side will stay on while the passenger side will alternate on and off with the high-side pressure. That's with some A/C manifold gauges hooked up and watching the psi numbers rise and fall.

Now if the A/C compressor is actually cycling on/off in the driveway, that "could" make both fans turn off at the same time. However, I've noticed that there seems to be a bit of a delay between when the A/C shuts off compared to when the fan shuts off. I actually like this because it keeps the fans from on/off/on/off everytime the A/C cycles. New Hondas for example. You'll hear the (noisy) radiator fans start/stop with the compressor when they're idling in a parking spot. I hate that.

327_TPI_77_Maro

iTrader: (8)

As stated, the AC is not cycling the clutch, it is engaged and running continuously. It's hard to say if both fans are starting and stopping at exactly the same time b/c it takes time for them to spin up and down, but they are definitely both cycling. I let the car idle tonight for about 10 minutes and the interior got ice cold w/ the AC running w/ the fans cycling like that.