Air Conditioning Control

[Gazbon008]

I was wondering if you had thought of adding control for the Evaporator Temperature - to prevent freezing

Some modern cars have a electronic sensor imbedded into the Evaporator which could be feed into a Spare ADC input

Adding some controls into the Air Conditioning Idle Up dialog box could facilitate cycling of the compressor to prevent Evaporator Freezing

The A/C Compressor Shutoff section could include an Input for the Evaporator Temperature and a value to shutdown the Compressor and a Hysteresis

MS3X in use on this vehicle

Cheers

Gary

[prof315]

Most evaporator temp sensors aren't temp sensors at all but rather switches that open at a certain temp. All you need to do is wire the temp switch in series with the A/C request signal ( and a pressure switch if you're smart) and presto no freeze up.

[Reverant]

Some cars do actually have thermistors, and others have a more elaborate scheme of two or more pressure control switches/resistors.

[Gazbon008]

Thank You for the information (prof315)

It did help me with the XJ Jeep I am working on

I still think the software feature I originally suggested is a good idea

Because as (Reverant) says some cars have a 2 wire thermistor such as the mid 90's Ford I have to do

Second as the output of some A/C Cycling Switches pulls High (such as the Jeep above) this means tying up the 12v Nitrous Input (or building an internal input into the Base) Some people might be lazy and want A/C plus Nitrous

Also as a Spare ADC would still work with a feed from a Cycling Switch - the value would change suddenly is all - setting a value < or > when the switch broke would work fine (Hysteresis set to zero)

cheers

Gary

[prof315]

Actually many cars especially in the late 80s and early 90s used a going High 12V "A/C is on" signal to the ECU and pressure sensors and that does mean using the 12v Switched input to make things work with a factory set up. Or use a relay to invert the signal to going low.

[Gazbon008]

Actually many cars especially in the late 80s and early 90s used a going High 12V "A/C is on" signal to the ECU and pressure sensors and that does mean using the 12v Switched input to make things work with a factory set up. Or use a relay to invert the signal to going low.

I was wondering about that but was worried
Would an electronic A/C Cycling Switch designed to send a signal to a ECU have enough amp/power rating to carry an automotive relay

This seems to me to confirm the value of using an ADC input because it handles all input situations - Switches pulling high or low and thermistors giving a variable result..

[prof315]

Would an electronic A/C Cycling Switch designed to send a signal to a ECU have enough amp/power rating to carry an automotive relay

Sure, when using a relay to invert a going high signal to going low, send the 12V to the relay coil, ground the other side of the coil and one side of the relay load contacts, and the other relay load contact becomes your going low signal to the ECU.

[Ghost]

I was actually looking for a similar functionality - I'm starting an ls swap and it would be nice to have a table that outputs a specific duty cycle based on evaporator temperature in order to run a variable displacement ac compressor.

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