FLYVMO

On a bench top power unit, each solenoid takes 0.31 A to activate at 13V.
At least mine which are at least 25 years old

Cheers!
Carl

BigAl1

THANKS Carl! That helps a lot.

hans14914

I have measured as much as 0.5a on the solenoids. A standard octal high-side driver would run them no problem. ST, Infineon, and ON all have nice single chip solutions with built-in fly-back protection for the inductive load. There are a couple digital pots out there that should work now, like the AD5290 or MCP41HVX1. That was kind of the stumbling point before. If you want to mimic the original design, you needed a digital replacement for a 1/8W pot, but you could theoretically use a DAC instead. I never tested this personally, but think it should work in the servo loop for temperature control if you are sampling external sensors instead of using the factory thermistor style sensors.

MjRocket

Let me know when your ready for a beta tester.

BigAl1

Thanks Hans - didn't know about those driver chips. I'm looking more for DIP packaging, and will likely run separate relays for the main outputs, with plenty of overhead on the current to allow for other uses if someone wants to try. The ***** I'm working with are 10KOhm 0.1W pots. The last challenge is the hot/cold pot output - converting it to replace the stock head's 200-1200Ohm resistance, trying to keep the mixing motor and thermistor sensor string intact.

BigAl1

Can anybody do some Ohm checking on the stock 928 HVAC control? Need to verify the resistance of the potentiometer controlled by the Cold/Hot slider, with no other temp sensors in the loop. Hoping to hear from several different model years (early to late). I'll start - my 1980 Euro S measures 750-1781Ohms. I am asking for more input because of the difference of 200-1200Ohm previously mentioned, vs what I measured on mine last night.

69gaugeman

I believe the WSM says 750 - 1750 is the proper range. I do know it's 1k total change.

BigAl1

Does the 750-1750Ohm range change for various years?

hans14914

All you need is to print or cut cams that fit on the back of the shaft to engage a min and max limit switch if you want to use a standard pot.

According to my old notes, the stock pot is 2.2k 1/8th ohm. It is used in a range of 200-2200 so a total of 2k range over 20 steps. Each increment in temperature is represented by a set of 100ohm.

I have some circuit boards here from when I was playing around with this to convert the factory card interface to ribbon cable. I can dig those out and send one to you if it helps.

I have a lot of documentation, schematics, and files from various efforts on this if it helps. Feel free to pm or email me.

AirtekHVAC

Al, I have a spare controller, that has unknown history...it is in fair condition...think it's from an 82. I will send it to you, if you need or can use it for testing. Also, I believe the solenoids are still intact, on the 84 parts car.....let me know what you need, I would be happy to be involved.

BigAl1

Thanks for the offer Ron! Not yet on parts testing, just concept and design phase. I'll do initial bench test with mine.

BigAl1

That is very generous Hans! I'll PM you.

parcon

Again, thanks for the wiring diagram. Seems the Altima control head while similar in appearance to the Sentra's uses different pin configuration, but otherwise seems nearly identical. I was able to get wiring diagrams for the manual temp controlled unit.

Pins
1 IGN (on/start)
2 BAT
3 GND
4 COMP ON (runs to BCM)
5 VACTR (runs to air door motors)
11 LT-ILL -
12 LT-ILL +
15 LAN SIG (feed back from air door motors)
17 FAN GATE (runs to Fan Control Amp)
18 FAN F/B (from F.C.A.)
19 FAN ON (runs to BCM)
20 IGN 2 (on only)
22 RR DEF SW (goes to BCM)
23 RR DEF SW (in from relay)
24 SENS GRD (goes to intake sensor ?)
25 INTAKE SENS (goes to intake sensor ?)
30 AC PD CUT (goes to ground)

Rear defogger, A/C clutch on/off and fan speed control seem straight forward to integrate. Going to get a new blower motor while it's ripped apart. Recirculate, Temp and Vents involve LAN and need more thought. Definitely not a plug and play conversion. Maybe head to a U-Pull It salvage yard and pick up the door motors to experiment.

M. Requin

Just FYI, when I was fooling around with this project, I found the following:
State Electronics, Part # L25392. This potentiometer is equipped with two limit switches that operate individually at each end of the pot's rotation, eliminating the need for cam operated microswitches. I requested a quote and got a price of 38.93 each, minimum 5 plus a 50.00 setup charge. That was in 2010.