Weird AC Amp - Idle Up Problem (1 Viewer)

[elripster]

So I replaced all of Mudhorn's AC parts that touch refrigerant last summer but never got the idle up to work. I had increased the idle to trigger the AC clutch and adjusted the RPM potentiometer to prevent any rapid cycling. I jumped back into this summer and what I found is that I have 12V on both the Blue / black and Yellow / Green wires which power the VSV that increases idle. Presently I have the VSV unplugged and I get that voltage on both wires at the VSV plug and at the AC amp connector as one would expect. Obviously, the Blue / Black should be ground switching so I should see a voltage delta between that and the Y-G. Likely, I just have a bad AC amp but I thought I'd see if anyone had ran into this issue and possibly fixed it.

Frank

 

[OSS]

The AC idle-up feature was a little perk specific to the FJ60. It really isn’t necessary. Just set the engine idle RPM to 800 RPM and forget about it. The AC won’t stall the engine and will run fine at 700 RPM.
If you want to boost it a bit when waiting at a stop light, pull out the choke cable a bit to bump up the RPMS.
Assuming you have the choke breaker system working

 

[elripster]

That's what I have been doing.

Frank

 

[elripster]

Well luck struck out of the blue, my buddy had one in a parts rig, I installed it and it all works like it should. I set the AC idle up speed to 1k and the vents feel colder.

Interesting, though the part numbers are the same the connectors are different colors. The green connector is the newer to the truck one. I guess something on the old part must have fried.

Frank

 

[S.CarolinaFZJ80]

@Engineer8000 can fix that.

 

[Engineer8000]

There is a flyback diode on the collector of the transistor that switches the idle up VSV to protect it when the VSV coil discharges. Could be it is leaky causing you to see +12 on pin 4.

 

[elripster]

There is a flyback diode on the collector of the transistor that switches the idle up VSV to protect it when the VSV coil discharges. Could be it is leaky causing you to see +12 on pin 4.

Thanks for the heads up. I might just replace that and have a spare.

Do you know how I spec and buy that? I am an ME but have been designing EV's for a long time so have some idea what you mean but don't know enough to spec the diode.

Frank

 

[elripster]

Is it this diode?

Frank

 

[Engineer8000]

I keep a pile of 1n4007 diodes in stock to replace these. I would need to check my file on these to verify which diode it is on the board. I will get back to you.

 

[elripster]

Thanks!

Frank

 

[crackdpot]

So, all I'd need to do is replace the component shown, and my AC wouldn't cause the revs to run up so crazy?!

 

[elripster]

So, all I'd need to do is replace the component shown, and my AC wouldn't cause the revs to run up so crazy?!

Assuming that diode is bad, and it seems to be on mine, it prevented the idle up function from operating at all as there was equal voltage on the VSV + and -. As a result the VSV would not trigger and send vacuum to the dash pot to increase the idle.

If your AC amp is triggering the VSV when it should but the idle is too high when it does I would suggest backing off the AC idle up adjustment screw on the carburetor first.

Frank

 

[Engineer8000]

It is the one below it