DME Pin 40, 41, and 50 Operation, Help Please

[Maych87]

This is my first post on pelican. I have an 89 964 and I am installing a megasquirt 3 engine management system. I am just on the final stages of getting all my accessories hooked up.

I am stuck on the AC system control through the DME. They are pins 40,41, and 50 on the 55 pin DME connector.

The only information I can find on these pins is they are all outputs and AC Compressor controls - The DME control unit receives inputs and sends output signals over terminals No. 40 (AC Compressor), No. 41 (AC Switch), and No. 50 (AC Heating System Regulation)

If anyone has any information on the
- operation of these pins
- If they are power or ground controlled
- What voltage are they
- Or any other information that will help me set up these pins in my Megasquirt engine management system

[Dmitry at Pelican Parts]

Hello and welcome to the forum! I've attached a link to our site's DIY tech articles on the 964 platform. There are several articles on the a/c system, take a look at them to see if they help you troubleshoot. If you need more details, please post a Comment just below the article and we'll have someone get back to you with specifics. Best of luck!

Porsche 964 and Porsche 993 Technical Articles Directory (1989-1998) | DIY Maintenance and Repair Projects for Porsche 911 model years 1989-1998 | Pelican Parts

[Maych87]

Originally Posted by Dmitry at Pelican Parts

Hello and welcome to the forum! I've attached a link to our site's DIY tech articles on the 964 platform. There are several articles on the a/c system, take a look at them to see if they help you troubleshoot. If you need more details, please post a Comment just below the article and we'll have someone get back to you with specifics. Best of luck!

Porsche 964 and Porsche 993 Technical Articles Directory (1989-1998) | DIY Maintenance and Repair Projects for Porsche 911 model years 1989-1998 | Pelican Parts

Hi thank you for the response. I had a look through the articles and was unable to find the information I was looking for. If there is anyone that could help that would be fantastic.


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[nickd]

I don't know too much about how the dme treats these, but have you followed them in the wiring diagrams? Do they terminate into the ccu? Many motronic cars use ac input to adjust the idle speed. I wouldn't expect the dme to do much more than that with these pins.

[Typ53]

Did you ever find out the signals to expect at these pins? I'm in the same boat now, looking for confirmation as part of a Motec installation.

It looks like DME Pin 40 senses AC relay open/closed state via 12V from the compressor relay;

Pin 41 senses condenser blower relay lo/high state, also 12V;

Piecing together info from BergvilleFX on CCU operation and the wiring diagrams it looks like DME pin 50 is the heater coast signal to prevent fuel cut on overrun when heat is required.

I can't work out the voltage value that DME pin 50 will see and whether 0V or some voltage is the trigger condition.

Can anyone confirm or deny the above please?

[Abijawara]

It sounds like you're working on an exciting project with your 964! The pins you're asking about are typically used for controlling the AC system in the stock DME. Pin 40 is usually for triggering the AC compressor, and it typically sends a ground signal to activate the compressor clutch. Pin 41 is generally related to the AC switch and might provide a signal to indicate when the AC is turned on, while Pin 50 is involved with regulating the AC heating or fan system. These pins are usually low-voltage signals, often involving ground control, but the exact details can vary by model year and system setup. Since you're using a Megasquirt, you'll likely need to either simulate these signals or adapt them to your engine management system to control the compressor and related functions correctly. If you haven’t already, checking factory wiring diagrams or looking into other Pelican threads with similar builds might provide more specific information on voltage levels and wiring details.