I spent several hours wiring up my manual fan switch following directions closely from ultimate fan mod and shoebox's OBD1 diagram using diodes.

First of all, the switch works well; turns on the fans & LEDs accordingly. My problems are:

1. LEDs don't light up when the PCM controls the fans (switch is off). I thought turning on A/C = high-speed fans? Neither LED comes on with A/C. No LEDs even when the car gets up to 3/4 temp guage mark.

2. With the switch off, the fans are still working since the car heats up to ~3/4 guage mark, then stays in the 1/2 - 3/4 range. I thought this was b/c the high-speed fans turn on too late and turn off too soon. The high-speed fans using the switch however seems a lot louder than when the fans are PCM controlled, even around 240deg, which I thought would engage the high-speed fans.

What could I have done wrong? I tapped the wires like this: http://users.oco.net/xero/fanmod/connectorwiring2.jpg and soldered & taped.

Please help, thanks a LOT.

Brian

 

Sounds to me like you did everything correctly.

The LED's aren't supposed to light up with the switch off.
So with it in the center position it's really just the same as never having done the mod to begin with.

 

i thought the differ read a couple times that PCM operation with the switch off will light the LEDs.

>> could this be because i used the diodes (OBD1) to prevent constantly lit LEDs with the car off, but they also prevent lit LEDs with the car on but switch off? <<

maybe? shoebox?

 

Only the low speed fans come on with the a/c. High speed is commanded by temp only. I would say that you may have wired the diodes in backwards if you are not getting the LED indication when the computer turns the fans on. The line on the diode should be on the switch side just like the diagram shows. Please verify.

Also, you are sure the fans are actually coming on when you turn on the a/c?

 

i will verify the diode direction tomorrow. i mocked it up the right way, but may have switched when making final connections after passing wires through the firewall. i have no constant-lit LED problems however.

i will also check that the a/c turns on the low-speed fans.

QUESTION: do BOTH fans operate at low & hi-speeds? or is one for low and the other for high?

can't see the fans well through the top, i'll have to ramp it up

THANKS a lot!

 

Yours should be a 3 relay system. Both fans run at low or both at high.

 

verified that the diodes are facing the right way (band pointed towards the switch), all other connections are good, fan switch/LEDs work fine on their own. PCM/LED operation is still missing.

- could the diodes be preventing lit LEDs under PCM operation? (i used two NTE156 SI, general purpose rectifiers: Phv 1000V Max, Irsm 60A Max, If -3A Max, Vf -1.1V @ 3A) they are black with a single grey band.

- also verified that the fans themselves are working, although the PCM doesn't turn on low-speed until the car is near the 3/4 mark on the temp guage, which is ~230deg? (correct according to shoebox ) this cools the car down to ~215deg till it bounces up again. i think high-speed comes on after a few cycles when it really gets hot

i will do a coolant drain/refill asap to aid the cooling, but i do still have the PCM/LED issue... plz help, THANKS.

 

You could jumper around the diodes to see if they are the problem or if you are using a switched source of power for the LEDs, you don't even need the diodes.

The reason the diodes were added in the first place, is because on some cars, one of the LEDs would stay on after the key was turned OFF (when using constant source for LED power).

 

edit: testing w/ jumper wire now

(being a certified electronics noob, i opted for the ciglighter; but i may have to change that eh?)

 

I jumpered around the diodes and the LEDs work with the PCM, yay... this however creates the lit LED when the car is off. win/lose situation

SO, it looks like the diodes will prevent constant LEDs but also prevent PCM monitoring, boo. I guess all OBD1 cars have to be wired via switched power souce.

 

I ran into the same problem when i did mine... Im not sure why it was doing it, but i have an easy solution. BTW, i didnt use the diodes when i did it on my 95 Z28.

Find the hidden accessory power feed wires (http://shbox.com/accy/Accessory.html thanks shoebox!). I'm pretty sure i used the pink wire as my hot wire. so its "switched on" when in the run posistion. I suppose you could use the orange wire also if you have the AU3 option so it would work in accy, run, and RAP otherwise it would just be a always hot if you dont have the AU3 option. I also used this as the ground, but it sounds as if you already have that covered.

hope this helps you out a little
Jeff

 

Those wires are only on Camaros (I used them, myself ) and he has a T/A, but there might be some close by that you can use.
I am not familiar with the Firebird dash parts to tell anyone how they come off.

 

oooh good point, i missed that he had a T/A. I'm sure there is some wire in the dash thats hot only in the RUN posistion.. The radio should have one, too bad i dont know which one it was. Sorry i couldnt be much of a help

 

Only on camaros...what a bUrn! thanks for trying though

Yea I didn't see any spare wires under the console (which btw comes apart pretty straightforward) in fact I soldered in extra lengths of wire to the + & ground since there's so little exposed to work with. A real pita.

I'm going to look for switched power next. I guess the radio is my best bet? Looks like we found a place where OBDII is easier to mod eY? haha

> how do you take off the radio bezel? i need to access the back <

thanks Jeff, Shoebox & all