A/C Tach signal mod for V8 Conversions

[djawahir]

So, I've finally got A/C in my V8 swap!

I've got a new model Vortec V8 (2007 Gen III L59 Flex Fuel engine). The engine PCM has blue and green connectors for those that know what I'm talking about.

I'm running every FJ60 Toyota A/C part except for the compressor, which is the one that came with my L59 engine. (It's still a Denso, just a different model.)

Now, I wired up the A/C circuit like I thought it was supposed to be wired. One of the signal wires coming out of the Vortec PCM is the tach signal wire. I thought I would just wire up this tach signal wire directly to my A/C amplifier tach signal wire and all would be well. Well, it doesn't work. (Since I don't have an oscilloscope, I can only assume that the PCM generated tach signal isn't strong enough for the FJ60 a/c amplifier to pick it up.

Enter the DEI 454T tach signal generator. This is a small device that sits on the alternator wire and generates a tachometer signal equivalent to the coil signal you would find on the original FJ60 with 2F setup.

 

[djawahir]

To wire up this DEI 454T, you will need:

red = +12V ignition (You can use battery, but then the device will drain some current all the time.)
black = gnd
black/gray stripe = generated tach signal (which will go to the a/c amp, tach gauge, etc.)

orange
green
yellow
white

The orange wire will either connect directly to the green, yellow, or white wire. In my case, and probably yours, if you are using a similar setup that I am using, you will connect ORANGE to GREEN.

 

[djawahir]

First, I needed to find a nice cozy place to mount my 454T. It has to be near the alternator wire since that will be how it generates the proper tach signal. I found a great place directly under the plastic Vortec engine cover.

 

[djawahir]

I have a Marshall's hardware store near me and I picked up a 1" x 1" steel L-bracket with 1/4" holes pre-drilled. (You can use whatever you like for a mounting bracket.)

I unscrewed the DEI 454T and modified the plastic cover with a 3/16" hole. Then, I bolted an M5 x 12mm bolt to the L-bracket as shown in the picture.

I reassembled the 454T as shown in the second picture. The L-bracket will securely hold the 454T in place.

 

[djawahir]

Then I just found some power and ground, hooked up the orange wire to the green wire and zip-tied the alternator wire to the underside of the 454T.

 

[djawahir]

Now, of course I checked that the red LED was flashing when my truck was idling to make sure that I was generating a tach signal from the 454T. Then I wired the black/gray stripe wire to the A/C amplifier tach signal (It's the black wire in the corner of the connector on the a/c amplifier).

Voila! No more putzing around with making my own circuits, doing a pullup resistor to the PCM tach signal wire, etc. This cost $20 and generates a good enough tach signal for my A/C amplfier circuit.

(I'm assuming that I will also be able to use the same signal to go directly to my stock FJ60 RPM gauge and it should be fine up to 4000 rpm. I'll post that in a new thread when I test that part out.)

 

[djawahir]

The good news is that with this tach signal generator:

You don't have to splice into any of the coil wires, etc.
It's also fairly cheap...I found one for around $20.
And you may be able to use it to control your original FJ60 tach as well as your FJ60 a/c amplifier.

I hope this helps anyone with a distributorless system looking for a valid tach signal!

 

[dbleon]

DUDE........ This is awesome!!

Thanks for doing the write up.

Questions:
1. The alt wire does not get spliced, correct? just sits on the backside of the module?
2. Where doe one find the Toyota A/C amplifier wiring you speak of?
3. Where does the compressor get power (from original Toyot wire I assume?)

 

[djawahir]

dbleon,

1. No wires get spliced in this setup. The alternator wire just sits underneath the 454T module. I ziptied the alternator wire to the module as per the instructions for the 454T.
2. The Toyota A/C amplifier tach wire is a solid black wire that comes out of the amp. On your evaporator box in the passenger side footwell, there is a 9 pin connector. The tach wire is the middle one. It's a solid black wire.
3. I just used the same compressor wire that ran to my old compressor on the new one. So, yes. the original Toyota wire supplies the power to your v8 compressor. (I just grounded the other compressor wire directly to the frame.

It's an easy setup and I will soon check to see if the 454T tach signal can run both my a/c amplifier and my stock 60 tachometer dash gauge...

 

[dbleon]

dbleon,

1. No wires get spliced in this setup. The alternator wire just sits underneath the 454T module. I ziptied the alternator wire to the module as per the instructions for the 454T.
2. The Toyota A/C amplifier tach wire is a solid black wire that comes out of the amp. On your evaporator box in the passenger side footwell, there is a 9 pin connector. The tach wire is the middle one. It's a solid black wire.
3. I just used the same compressor wire that ran to my old compressor on the new one. So, yes. the original Toyota wire supplies the power to your v8 compressor. (I just grounded the other compressor wire directly to the frame.

It's an easy setup and I will soon check to see if the 454T tach signal can run both my a/c amplifier and my stock 60 tachometer dash gauge...

Very cool my friend!

This will help me greatly!!

 

[Clonestocker]

Somebody's Lurking

 

[djawahir]

Update: After installing the DEI 454T tach signal generator, the A/C started blowing really nicely...at high rpm. And that was after turning the blue dial on the A/C amplifier all the way to the right.

I think with the 2F engine and coil, the manual says that the range on the blue dial is between 600-900rpm. So, I'm assuming that the extra 2 cylinders of my V8 makes a difference in the signal that gets seen by the A/C amplifier. (Since I don't have an oscilloscope to measure any of this, it's plain wild a$$ guessing!)

Since the price of gas keeps me from just changing my V8 engine idle to 2000rpm for cold A/C, I decided to modify my A/C amplifier instead.

 

[djawahir]

The blue knob on the A/C amplifier is a 10k potentiometer. If you look on the back of the circuit board, you will see that two of the pins are glob soldered together. One pin stands all by itself.

You will be adding one side of a 10k resistor here at the single pin.

But first, you have to cut the copper trace that runs from the single pin of the pot to a resistor. After doing that, you will connect your 10k resistor between the single pin of the pot and the pin of the resistor along that trace you just cut. Hence, making a new electrical connection through your resistor instead of through the trace. Got it?

After this mod, you should be able to adjust (clockwise) the A/C amplifier blue dial down to around 800 rpm for your V8.

 

[djawahir]

Here is a picture that speaks a thousand words.

 

[djawahir]

And I need to give a shout out to Rex at CoolStream A/C for helping me sort out my custom air conditioning hoses. He was very helpful and patient with me in figuring out what I needed. Good service definitely goes a long way. If you can, please support another MUD member/vendor. His tag is Coolstream.

Thanks Rex!

 

[dbleon]

Awesome! How on earth did you figure this out??

 

[djawahir]

Awesome! How on earth did you figure this out??

I stayed at a Holiday Inn Express...?

I used to tinker with electronics in my younger years.

 

[Elbert]

There are other options on getting the A/C to function with a V-8 swap, but as is true most of the time there is more than one way to approach a solution. There may be different issues between the various GM V-8 engines.

My tach signel wire from my 5.7 PCM feeds the wire that use to connect to the negative side of the I-6 ign coil.

The A/C idle up function is my next task to figure out when I get through messing around with all the other stuff I want to do.

 

[dbleon]

I stayed at a Holiday Inn Express...?

I used to tinker with electronics in my younger years.

Its a darn good thing you did..

I think I will do like the Japanese and copy your knowledge.

ouch