I have a 92 D250 CTD 2WD with the 518 auto that I've converted to lockup. I'm using a Hobbs pressure switch off the governor pressure port to activate the ground circuit for the L/U solenoid. It is tied to the O/D ground circuit so I don't get L/U unless it's in O/D. But this method leaves a little to be desired because at certain speeds I get an annoying, in and out of L/U action. Normally it's not a problem but getting caught in traffic sometimes I can't get around it without slowing down. So what I'm looking to do is find a way to activate the circuit at a higher speed or pressure and have it stay engaged until it reaches a lower speed than the activated speed. Maybe a 5 MPH difference or something. I've not been able to find a switch like this in my internet searches so if anyone has any ideas I'm all ears.
Thanks.

 

Go to RockAuto.com and look at A/C compressor switches. When you find one, look at the description. There is a little blue "info" button after the part name. It will give you the info they have on the part.

The Four Seasons 35800 switch turns on at 49 psi and off at 22 psi. I do not know the thread pitch.

 

You want a pressure transducer and not a pressure switch. I think it was $~65 ish. Default was 50 psi which works about right for me even though it is adjustable.
The transducer has an activation pressure (50 psi) and the fallout pressure is (40 psi), so it doesnt hunt for OD.

M

 

That would work great but while searching for pressure transducers I find there are many different kinds. I have no idea what type I need or really where to find them so if you could give me some insight as to the manufacturer, type of switch, where you bought it or even a part number that would help greatly.

 

Those switches won't work for me. My governor pressure at 60 MPH is 90 PSI, it's 45 PSI at about 30 MPH, that is way to low of speed so I need a higher rated adjustable switch or transducer.

 

Check this out, I use Automation Direct all the time. At 89 bucks, probably more money than you really want to spend, but it is the cheapest I can find a switch that should work.

https://www.automationdirect.com/adc...PSD25-0P-1450H

https://www.automationdirect.com/sta...seswitches.pdf

The good thing about Automation Direct is they have very good CS technical help and even their forum is full of good help.

 

I don't mind spending $90 on a switch but what concerns me about this one is the operating temperature of the fluid which could reach upwards of 250 degrees. The spec they have listed for both operating temp and medium temp is -13 to 176 F.

 

Didn't think of that.......

You might give them a call and see what they might have to help you out.

Another less attractive choice would be to use a pressure sensor and one of their cheap PLC's ( the Click ) to make a custom setup, I use them in various control schemes, cheap, easy to program and reliable.....

 

I would recommend the Compushift mini for this application. I am installing on right now on my 1973 D200 with A518, however it has logic to control a lock up T/C as well, and the "tune" can be fully custom to your preferences/application.

COMPUSHIFT Mini for Chrysler A518/46RH and Chrysler A618/47RH - Twist Machine

 

That is what I'm putting on my 92. They put their pressure switch in the front servo port so OD will turn on in 3rd and 4th.

 

If it is a hobbs switch, remove the rubber plug on the top center of the switch, and adjust the pressure with an allen wrench. They are adjustable by about 10%.

 

I have adjusted it but there is still that annoying contact chatter right at that pressure. I got a schematic from the Moparts forum using two Hobbs switches and a relay. Looks to be the easiest way to accomplish what I want to do.