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 3.4 swap - A/C
#607926
05/27/05 10:06 PM
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Joined: Dec 2004
Posts: 42
OP
Getting the Wheeling Fever
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I have a 94 Runner with a 97 3.4 swapped in. The A/C does not work.
I suspect it has to do with the tachometer signal. The A/C amplifier uses the signal to shut off the A/C compressor when RPM is too low and too high (I think).
Now, we all know you have to do the tach mod to make the stock 3.0 tach work with the 3.4 motor. So logic tells me the different 3.4 tach signal also messes with the A/C control.
Can anyone confirm this? Has anyone found a fix?
94 4Runner, 5VZ-FE, A340H
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Re: 3.4 swap - A/C
[Re: 5VZ]
#607927
05/30/05 07:32 PM
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Joined: Dec 2004
Posts: 42
OP
Getting the Wheeling Fever
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I put 1, 5, 8, 9 and 14 volts into the tach signal and nothing.
Anyone know what the tach signal for a 3.0 looks like? Is it a varying voltage or frequency?
94 4Runner, 5VZ-FE, A340H
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Re: 3.4 swap - A/C
[Re: 5VZ]
#607928
05/30/05 07:37 PM
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Joined: Jan 2000
Posts: 12,153
Web Wheeler
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It would be a 12V square wave off of the ignition coil, frequency proportionate to the RPM.
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Re: 3.4 swap - A/C
[Re: 4Crawler]
#607929
05/31/05 03:46 AM
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Joined: Oct 2003
Posts: 2,661
Roll Me Over
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this topic interests me since I might do a 3.4 & live in FL.
94runner: Dana 44 SAS, 35's, Lockers, gears, winch, rock rails, bumpers, 3"BL, drivetrain lift, Budbuilt cross member, centerforce clutch and MORE! ***FOR SALE*** $8,500 -1985 Supra (STOCK!) FOR SALE $4,000 www.celicasupra.com
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Re: 3.4 swap - A/C
[Re: J94_4runner]
#607930
06/01/05 02:10 PM
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Anonymous
Unregistered
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Use the tach signal from the 3.4 to supply the stock A/C amplifier. I wired my 3.4 tach signal up to the same pin as the factory 3.0 tach signal and, while the tach didn't work until I modified it, the A/C worked like a champ.
The output signal of the 3.4 is clean 5 volt square wave, if I remember correctly. The output of the 3.0 looks like a large spike (upwards of 12 volts) as it's derived from the coil output. Like Roger said, it's in synch with the RPM.
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Re: 3.4 swap - A/C
#607931
06/02/05 12:27 AM
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Joined: Dec 2004
Posts: 42
OP
Getting the Wheeling Fever
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If Willcipher's worked, I guess something else is wrong. I will keep diagnosing.
Unfortunately, I bought the truck, then swapped engines immediately. I never tested the A/C when I had the 3.0 in it. So, I don't know if it is a pre-existing problem or a result of the swap. I'm regretting that.
Thanks for the replies.
94 4Runner, 5VZ-FE, A340H
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