327_TPI_77_Maro

iTrader: (8)

I have a stock 89 trans am 305 TPI w/ dual fans that I just repaired the AC system on and now I see that idling with the engine cool and the AC on, neither fan runs. When the high side exceeds ~235 psi, both fans kick on, run for about 10 seconds, then shut off, then they keep doing this on/off behavior as the high side pressure rises and falls due to the condenser airflow changing w/ then on vs off. My AC is not cycling, it is charged correctly and stays clutched in when running.

I keep reading that people are under the impression that the ecm controlled fan should run constantly at idle w/ AC on but looking through the 165 bin this does not look correct. It looks like below 8 mph the AC on tables are always used, and above 8 mph either AC off or AC on tables are used depending on whether the ECM is receiving an AC commanded signal. It also looks like if the secondary fan kicks on either due to the temp in the cyl. head temp sensor being exceeded or from the high pressure switch in the compressor being activated, the ecm receives an aux fan command signal and the ecm will force the primary fan on if it was not already running.

So is it normal for my dual fan 1989 to only run both cooling fans when the high pressure switch cuts in, and then to shut off when the pressure drops below 200 psi? Such that I do not have the primary ecm controlled fan running constantly just because the AC is on, if the engine does not otherwise need to be cooled due to temp?

Thanks, Steven

TPI-Formula350-

I control my drivers side fan in the tune in the scalars/constants. It will turn on or off in park or gear according to my scalar settings. The passenger fan if controlled off the temp switch in the passenger side head and if the ac is on I believe. I just put the passenger fan on a toggle switch.

327_TPI_77_Maro

iTrader: (8)

I am troubleshooting at this point and I don't want to mess with how the stock tune controls the fans, I am just curious if what I am experiencing is correct according to the factory tune. I was surprised to see the primary ecm controleld fan is not running all the time w/ AC commanded but then when I looked at the bin it seems that it shouldn't. But this seems to go against what the common wisdom says around here?? I keep reading in stickies in the cooling system section that a dual fan car should have the ecm controlled fan commanded on any time the AC signal is received, but I don't understand how the 165 bin would do this the way I'm reading it?

I am getting really cold AC and the low/high pressures are good but I just want to make sure this fan behavior is normal before I break something, it seems kind of hard on the AC system to be letting the pressure keep hitting ~ 250 psi by the time the condenser airflow is sufficient to drop the high side pressure.

utilityguy2

iTrader: (1)

This is what I believe is normal from looking at the wiring diagram. The auxiliary fan is powered by the aux. fan relay which closes anytime the alternator is putting out 12v.
the Fan on is initiated by one or both of two things, the temperature switch in the head or the AC pressure switch. Fan 2 is independent of fan 1 and is mostly mechanical in operation. There shows an input into the ECM at D11 but it is a 12v input so don't know what that does other than to tell ECM it is powered?? I suppose there is a draw down of voltage if any of the 2 switches close and fan is on. I do know in the ECM programming there are no settings or mention for fan 2.

327_TPI_77_Maro

iTrader: (8)

Fan 2 kicking on based on the high pressure switch is definitely causing the ECM to kick fan 1 on with it so it must reference that D11 input, not sure though.

My question still is then, is it normal for fan 1 to not run all the time when the AC is on at idle? Or is my ECM shot? I have a bucket of spare 165 ecms in the basement so I will swap it out if something is wrong with it.

utilityguy2

iTrader: (1)

Going through the 89 bin file It also looks like the duty cycle tables are only used above 35 mph. also it won't turn on with the A/C on until car reaches 20 mph. Even if all of the minimums are met the fan must stay on for 10 seconds even if temperature drops below off set point. I'm not an AC guy but doesn't seem right that the A/C pressure switch is closing and the pressure is so high to cause that. Maybe someone else knows about that process.

327_TPI_77_Maro

iTrader: (8)

The switch is only 235 psi, that is normal for an AC system w/ no fan running and a full charge to hit that figure. As soon as the fan runs it pulls down to 200 psi. On most cars a fan of some sort would be always running w/ the AC on specifically to keep the condenser cool so your high side pressure is appropriate, hence my concern for the fan not running until the pressure spikes, which is normal if you don't cool the condenser.

utilityguy2

iTrader: (1)

My previous response seems to indicate that ECM will not command fan on for any reason relating to A/C unless you are going 20 mph and using the duty cycle tables. Do your numbers match mine in above post?

utilityguy2

iTrader: (1)

Fan two is running. If not your aux. coolant fan switch is no good. I don't know what temp that is set for but surely it is a low temp.

327_TPI_77_Maro

iTrader: (8)

It depends on the bin, in some tunes the min speed is 8 mph not 20, and my understanding was that min speed isn't when the fan kicks on w/ ac, it is when the ac on vs ac off tables are used. I'm really not sure though, I have never used '165 with a car with functional AC before. I have never seen a car where there is not at least a low speed fan always running @ idle with the AC on...the system would self destruct from the high side pressure running so high w/ no airflow across the condenser.

Fan 2 is working correctly, I need to know why fan 1 is cycling w/ the AC on at idle and not just running?

utilityguy2

iTrader: (1)

You are right and I think I know why. D11 probably is an ground from the ECM when A/C is on. It acts like a separate switch in addition to the other 2 switches.so there are three conditions to turn fan 2 on. ECM commanded (A/C on), high pressure switch, high temp. switch.

That now makes sense. So if A/C is on then Fan 2 is on always. By the way, I was reading a 89 350 bin the 305 is as you say.

327_TPI_77_Maro

iTrader: (8)

Ok so the next question is, why do neither of my fans run constantly w/ the AC on (one should or else my AC system is going to self destruct soon from lack of condenser cooling). Both fans porpoise on/ off constantly even though the AC clutch is staying engaged and the AC is running continuosly? Other than a faulty ECM I can't think of any other reason why this is behaving like this....

utilityguy2

iTrader: (1)

"my understanding was that min speed isn't when the fan kicks on w/ ac, it is when the ac on vs ac off tables are used."

I may be missing something but I see no A/C on and off tables, there is only the duty cycle table and if you look in that you'll see all temps are for 99.6 duty cycle. Seems to me a waste of programming space for only.4 savings. But ...

327_TPI_77_Maro

iTrader: (8)

I meant when it switched from ac on temp to ac off temp tables, not duty cycle. Yeah I don't know why there is a duty cycle table when its not actually a PWM fan

utilityguy2

iTrader: (1)

I suppose it's going on and off at 5 second intervals because it has tripped the pressure switch because the aux fan is not on. If it was mine I'd check D11 to see if it is indeed a ground which means the fan should be on. if there is no ground the ECM is not commanding it for some reason. Possible ECM related. Also you can ground out the switch in the head and see if fan comes on as it should. if it does the switch is probably OK. and we know the pressure switch is OK as it turns fans on.

utilityguy2

iTrader: (1)

remember, only 3 switches turn fan 2 on. temp, pressure, ECM I think we can possible rule out first two.

327_TPI_77_Maro

iTrader: (8)

Ok will report back, I will hook up my ALDL cable and watch and see if the ecm is reporting that the AC is always commanded or if for some reason it does not know that (broken wire?). It sounds like my 2 options are either the ECM doesn't know the AC is on, or the ECM is bad.

utilityguy2

iTrader: (1)

Yes if the signal wire at B8 going to A/C is broken it would also not work.

anesthes

iTrader: (12)

Both fans come on when the A/C pressure switch closes. (1600kpa)

(From the actual service manual)

action: With engine cold, and idling, turn A/C to NORM.
VIN E: Coolant fan turns on
VIN 8 & F: Coolant fan & heavy duty fan turns on when A/C head pressure exceeds 1600 kpa.

The system is working properly. When the car is moving, the A/C condensor is cooling. If pressure gets too high (your idling stopped) the A/C pressure switch will trigger the fans to come on.

-- Joe

327_TPI_77_Maro

iTrader: (8)

Ok Joe so is it then normal for there to be NO fans running on the Vin F car until it trips that 235 psi switch? So my fans cycling, basically managing the head pressure of the AC 200-250 psi, is normal? Seems a little scary but I guess that would almost be duty cycling the AC without turning the clutch on and off. Thank you for replying, this would make one of the threads in the cooling section which claims fan 1 should always be on with AC commanded completely incorrect, which is what initially confused me.

anesthes

iTrader: (12)

Correct, it is normal. A lot of the forum information is wrong because people think the way the car they own operates applies to everyone. There were year to year changes, different designs based on the VIN, etc.

I just ripped all the A/C our of my '88. Need room for the intercooler.

-- Joe

utilityguy2

iTrader: (1)

I'm sure the manual is correct. But on mine, as soon as you turn on A/C the ECM (I believe) turns on fan 2 and it stays on. I think the pressure switch maybe is a safety switch if pressure gets too high it turns on both fans. But I'm not a expert on A/C. Only my experience on my cars.

327_TPI_77_Maro

iTrader: (8)

Thank you for clearing this up Joe, you just saved me an evening of frustration!

anesthes

iTrader: (12)

What year is your car? Stock ECM or updated prom ?

My manuals are actual GM manuals from the pontiac service group. Not helms or reproductions or anything like that. They have come quite handy over the years in fixing cars with broken wiring harnesses

-- Joe

utilityguy2

iTrader: (1)

Going through the programming for your F body 5.0 car and the wiring diagram has convinced me that it is not normal but that is my opinion and as you know, everybody has one.

Don't know where that leaves you but I'm sure other, more experienced guys will chip in with their knowledge.

327_TPI_77_Maro

iTrader: (8)

I wired another TPI car as an 89 Firebird and used the 165 ECM and with AC, the AC on signal to the ECM does not force that fan on either, so this seems to make sense, and I don't see anything in the bin for the 89 TPI cars that would run one fan at all times w/ AC on. It just seemed like odd logic for the factory to cycle both fans, counter intuitive to what I have seen on other cars in general, but if thats what the manual says I am ok w/ that. The AC blows super cold and the system pressures are good. As long as it's not going to destroy itself.

utilityguy2

iTrader: (1)

I've had well over 100 cars and I think they all (that had electric fans) worked that way but you are correct in this group there are so many variants and hacked bins that always wise to ask. My current is the Vette with 88 Camaro engine and harness. But had a 85 T/A recently that worked that way (fan 2 on) so just going by the wiring diagram tells me something and the bin some more that is what I based my opinion on. But will be glad to change it if I'm wrong.

327_TPI_77_Maro

iTrader: (8)

I agree in that I have never seen another car of any make with electric fans that did this (cycle the fans w/ AC on to regulate condenser temp/head pressure) which is why I was confused. It looks like it achieves the same thing as a PWM fan without actually being PWM

utilityguy2

iTrader: (1)

There are lots of things in a bin that you don't see. I think D11 grounding when A/C is one of them or I can see no purpose for a wire to D11.

utilityguy2

iTrader: (1)

I have a test stand with a 165. I will try the d11 ground scenario and report back with any info. that may help you, me and other as to what turns fan2 on besides pressure and temp.

327_TPI_77_Maro

iTrader: (8)

Knowing the AC is on via D11 will cause it to use the different cooling fan temp tables for fan on/off at least. Yeah def. let me know, both of my 6E mask 165 TPI setups do not force the fan on w/ AC request signal on D11 being on.

anesthes

iTrader: (12)

What mask are you running?

-- Joe

utilityguy2

iTrader: (1)

$6Eextended with apym bin.

OK back to square 1. D11 is a 12v output which ties in with a 12v from the alternator. the only reason/purpose I can see for this is the ECM will possibly see the draw down of voltage when any switch is closed/grounds. I wish I was a electrical engineer to see the purpose of this but I'm not.

Bottom line, Moderator and others are correct as I see no other way that the fan 2 can run unless reaches A/C pressure switch limit or Temperature fan limit. I don't see how fan 1 and 2 are connected in any way unless it is thru D11 and that would need to go from 12v to ground which I don't think possible.

I'm sure other more learned people will respond but I'm stumped. But I know one thing, if it was my car, it would not work that way. It would work the way I thought it did. And as my car now does. But I wired that.

utilityguy2

iTrader: (1)

327 - I still don't get where you see different cooling fan tables? I see no tables for fans. But, I may be blind.

327_TPI_77_Maro

iTrader: (8)

I meant to say scalars. Fan 1 on ac off, fan 1 off ac off, fan 1 on ac on, fan 1 off ac on. Hence the ecm needing to know if ac is commanded or not, to decide which scalar to use, which is modified by some minimum speed scalars.

utilityguy2

iTrader: (1)

Ah Yes. that makes sense. the A/C on signal comes into the ECM on B8. it is 12v whenever the A/C compressor is engaged.

327_TPI_77_Maro

iTrader: (8)

^^I am tired and making mistakes because I stayed up so late trying to figure out why my fans were working incorrectly, when it turned out they were in fact working correctly.