the flyin' scotsman

Given the number of inputs to the HVAC control head what intelligence is applied to which actuators to open or close? I believe the auto system has little issue (when operating properly) when outside and inside temps are quite different.............my query really is the decision making the head unit applies at the many input situations; outside air temp, inside air temp and the temp selection lever ie. which input signal has priority? (any other EE's around today?)

Ketchmi

I'm not sure it has anything to do with logic...

69gaugeman

I've started to design a climate control head replacement that will be electronic and user a micro processor. The system is actually very simple and the inside and outside temperature sensors are in series with the temperature slide lever. That means that it controls temperature based on the difference between outside and inside temperature relative to the slide lever. I intend to offer both a direct replacement and a version that will show the outside temperature as well (would require a little rewiring).

Where in alberta are you? I spent a lot of my youth in Calgary as well as two of my kids were born there.

Rod

BrianG

Great idea Rod! I'd bite on something like that!

I too was raised in Calgary, but I've grown up and moved to Edmonton, now!

69gaugeman

Brian,

That must mean you have to work for a living.

BrianG

Unfortunate, but true!

heinrich

I'd prefer a simple pushrod cable replacement sytem. Open, shut, on, off. Manual. Driver controlled. Never fails.

69gaugeman

Malcolm,

The head really does not do very much. The control unit does all the thinking. The head just sends signals to the vacuum solinoids to tell which flaps to open and to tell everything when the A/C is on. It does some other little stuff like turn the fan on full when in defrost etc. My advanced system will have infinately variable fan speed that would come on only when the system was warm enough (for us northerners) and slow down when the temperature was correct.

69gaugeman

had a beetle with one of those... never worked

the flyin' scotsman

Rod...............2 1/2 hrs south of the city in an area generally know as the Crowsnest Pass.................we're forunate to have 40 acres on the Crowsnest river and lots of room for toys with no people presuure to be concerned about.

the flyin' scotsman

So what does the control unit do? If the temp lever is set to 18 and the outside temp is warm (perhaps July in this part of the world) and the inside of the car is warm (been sitting in the sun) does the control unit select the recirc solenoid automatically? If not whats the purpose of the outside and inside temp sensors?

As Dave said............where's the logic?

As I've mentioned in other posts perhaps a modified HVAC system would delete the centre comb actuator (more trouble than its worth) and perhaps the inside and outside temp sensors.

As H said............go manual.

69gaugeman

Malcolm,

It basically controls the coolant valve and the 'impact wall solinoid'

the flyin' scotsman

Understood, so the coolant valve solenoid is switched to allow heat to the cab and the inside sensor sends a signal to the control unit indicating the desired temp has been met which un-switches the coolant valve solenoid. This happens in parallel to the outside temp sensor that when the o/s air temp is highr or lower than the temp lever setting a signal is then sent to the recirc solenoid to acitvate or not ?

Is this accurate?...........the WSM does a poor job in explaining.

WTH is the 'impact wall solenoid'?

69gaugeman

Close, the two temperature sensors and the lever are all in series (one after the other) as one goes down the others stay the same. Basically there is a voltage that goes to the controller. I have not yet studied the controller in depth but basically if the outside temperature is low and the inside temperature is low and the slide position is high it turns on the heater valve. as the inside temperature rises the voltage signal drops to tell it to close the heater valve. if the outside temperature rises it has the same effect as the interior temperature rising. It then shuts off the heater valve and just puts in air from the outside. Cooling is the same but in reverse. I haven't checked voltages yet but I asume that stable is 2.5volts heat is above that and cool is below that.
There are some other things such as when a/c switch is on will not turn on heat etc..

Damn it if you keep me thinking about this I might have to eliminate the controller too. I want to do one thing at a time ok!!!!!!!!

the flyin' scotsman

Rod..........that's what I assume also and without the input from the temp sensors the unit would then operate in a relative manual mode........forbid that the driver would have to make such a drastic decision......too hot move the lever to a cooler selction and vice versa.

I believe when the a/c switch is on there are certain defaults; coolant valve solenoid is switched to apply vacuum and no heat and the recirc solenoid is switched to open the recirc flap; similar defaults apply when the lever is switched to defrost.

Sorry for making you think on New Years Eve..............go have a drink.

Its +9C here................I'll take my car for a little run, quick wash and perhaps go fishing this aft.

Happy New Year!!!