Automotive Air Conditioning Information Forum

Hey all,
Converted a 99 Porsche boxster to EV.
Am building a Tesla EV compressor based system. Currently have the system fully flushed, proper oil, EV dye is on the way.
Originally I thought I could intercept the compressor clutch signal from the HVAC head, but Porsche uses the cars computer to actuate the compressor based on many different inputs.
I've been trying to fake out the computer because it needs things like Throttle valve position, RPM, coolant temperature, intake temperature and I'm not sure what else in order for it to operate the fans and clutch. Was making progress but it's becoming harder to figure out what inputs need to be faked out for it to operate.

My question is
The only input coming from the AC system is mean pressure and high low pressure from the pressure switch. H/L is easy it passes 12V when there's enough but not too much pressure.
But the mean pressure.... What is the car looking at there to regulate the compressor clutch?

I can build a controller if I know the operating conditions of that pressure switch.

Or in other words, how can you manually control a TXV system on a Porsche.

Thanks
Jesse

Typically the climate control for an engine driven compressor is madly trying to sort out the wildly variable engine RPM, the need for condenser fan speed vs road speed, engine temperature, cabin temperature and heat load. The Porsche will cut power to the clutch beyond a certain RPM to keep the compressor from over speed damage...

I don't know anything specific about what Tesla is doing for a compressor. I do know about the HVDC compressor in the Equinox Hybrid however. Can you describe the Tesla compressor operation?

I would spoof the Porsche ATC with some middle of the road parameters. IAT would be ambient temp. RPM 2850. TPS about 25%. Coolant temp 200f.

That will get you started.

The high side pressure feedback tells the ATC when to run the condenser fans, and at what speed.

The HVDC compressors I know about use the CAN bus to drive the inverter located in the compressor. A variable speed compressor, using a 3 phase motor and a scroll compressor.

This means your interface will need to regulate the compressor speed based on cooling load. The Porsche simply drops the compressor clutch engagement when the evaporator approaches freezing. All or nothing.

An interesting project. The Equinox does better than most engine driven compressors at idle and low speed. You get full compressor output sitting at a stoplight, something that is not available otherwise.

Why do you believe the Boxster uses mean pressure? I've never heard of that, and I can't think of why it would be built that way. When a pressure transducer is used it's usually high side pressure. Your Boxster used an internally controlled variable compressor, so it would take care of cooling capacity by itself.

Valid point Detroit if his Porsche has the electric control valve in the compressor. My parts listing shows the Boxster with either the electric control valve OR the clutch type compressor.

In the case of the control valve, he would need to translate the Porsche control valve PWM to a signal for the CAN bus electric compressor control input.

It's internally controlled variable meaning a control valve, but it's entirely mechanical, no wires, it controls compressor by itself using only pressures