Vehicle HVAC questions

[prisky]

Hi

My name's Dave and I'm located in Australia. I have just recieved a new company car, known as a GM Holden VE Commodore station Wagon. The vehicle uses and Air International Thermal Systems HVAC module with a Denso ECVD compressor. I believe the manufacturer is being quite conservative with their air conditioning effeciencies. The operation seems to cater more for fuel consumption than performance. Putting it basically it just doesn't get cold enough. With reasonably high ambient temperatures (around 35 centigrade) the vent temperatures start off around 5 degrees and within a very short period of time step up to 9, then 12, then 15 as the interior cools slightly. This is with the temp control set as "C" for cold and the vent on recirculate. The HVAC accepts inputs from an outside ambient temperature sensor, and inside temperature sensor via an aspirator, a photoelectric sun load sensor and an evaperator temperature sensor. My question is can I substitute a resistive load to one of the sensors, for example the interior temperature sensor to indicate to the HVAC module that the interior temperature is in fact hotter than it is? My guess is the compressor would not be cycled down as much and vent temperatues may remain lower? Would I also need to modify the outside ambient temperature sensor and possibly the sun load sensor? Hoping someone out there may be able to assist. I can provide a URL to a site with further details particular to my vehicle if required. Thanks, Dave

[charlie patt]

if you are running a 35 ambient aint 15dc air of the coil is enough? in good old sunny england if we get 20dc diff thats as good as it gets, as far as your sensor adjustment the main controlling issue is the evap sensor we reposition those if colder air is required citroen done this al of a sudden air of was cutting of at ten dc when there older citroen would do 2 dc THIS IS ON THE PROVISION THIS IS A AIR SENSOR AND NOT A ICE SENSOR. THE biggest influence we find is the lack of insulation on new vechicles due to weight and cost and manufactuer looking to save money the vechicle would cool better on the road due to the air under the vechicle cooling exhausts etc. i would have a word with your dealer in your area and sea what they say due to ac systems being built to a cost or that what it seems to be happening a recirc flap thats not working makes 5 dc diff or 100grms of gas short the same ? a system with rear ac with starve the front ac? if you have a red hot ambient say your 35 dc when you step out of the car if it is pumping out 5dc you will probable have a bad headache or worse as gm and ford found out several years ago

[prisky]

Hi Charlie

I'm not saying I'd like 5 degrees constantly, just maybe a little longer than the HVAC currently decides. As you've mentioned the vehicle interior absorbs so much heat that as the HVAC throttles off to around 15 degrees I'm fighting a losing battle. I know the system has the capacity as on a recently hot day (40 centigrade) with the car in the sun parked for a couple of hours the vent temperatues went to -1.5 for a short time before easing back to around 9 degrees. Perhaps I'll try bypassing the in-car temperature sensor with a resistor of value which would indicate to the HVAC that the in-car temp is a constant say 40 centigrade and see what happens to the vent temperatures then? I think the evap sensor may be difficult to get to, as is the sun load sensor. Any other ideas would be appreciated, especially as I just heard the forcast for today and we're heading for 39 degrees again!!!

[cadwaladr]

my idea of a holden was some hypercharged gas guzzlin tyre squealing getaway car,windows down with uzis poppin out shoutin feck you.

[Rob White]

.

I have no answer for the question but is it possible it is set
to draw in fresh air (at +35 degC) as apposed to recirculating
the air in the car?

Regards

Rob

.

[prisky]

.

I have no answer for the question but is it possible it is set
to draw in fresh air (at +35 degC) as apposed to recirculating
the air in the car?

Regards

Rob

.

Hi Rob

Hopefully not, control set to recirculate and it seems cooler on this setting, damn computers deciding when you are allegedly cool enough....

Dave

[Rob White]

Hi Rob

Hopefully not, control set to recirculate and it seems cooler on this setting, damn computers deciding when you are allegedly cool enough....

Dave

Your on your own then mate

In principle finding the internal probe and installing another
sensor or adding a resistor to fool the controller is possible,
but there lays your problem, finding the probe and frigging it.

All the best

Rob

.

[install monkey]

can you not put a straw or similar tube sized implement over the tipoff the sensor so it is less responsive, saves ripping the dash out to try and bodge!

[fridgability]

I fink you is jus tryin to pi?? us off about our weather here in Blighty,

[stufus]

can you not put a straw or similar tube sized implement over the tipoff the sensor so it is less responsive, saves ripping the dash out to try and bodge!

Is that Monkey's version of a (bell)Endocube ;-)

Cheers
Stu

[mikeref]

Hi Rob

Hopefully not, control set to recirculate and it seems cooler on this setting, damn computers deciding when you are allegedly cool enough....

Dave

Just to add to your dramas, some vehicles have IR sensors aimed at you and your passenger. This gives onboard computer more control over supply air temperature by mixing air off heater coil through a "Blend door"
I have the model before yours, the VZ and it doesn't use IR or sunlight sensor. It just uses the variable drive on compressor. More questions now right?

[mikeref]

my idea of a holden was some hypercharged gas guzzlin tyre squealing getaway car,windows down with uzis poppin out shoutin feck you.

Had to laugh because your perception is mostly true. Strict control on weapons though.

[prisky]

can you not put a straw or similar tube sized implement over the tipoff the sensor so it is less responsive, saves ripping the dash out to try and bodge!

Have to find the evaporator temperature sensor first, any one know exactly where it's located?

[prisky]

Just to add to your dramas, some vehicles have IR sensors aimed at you and your passenger. This gives onboard computer more control over supply air temperature by mixing air off heater coil through a "Blend door"
I have the model before yours, the VZ and it doesn't use IR or sunlight sensor. It just uses the variable drive on compressor. More questions now right?

Yes, more questions. I located the internal temperature sensor and temporarily replaced it with a resistor that would indicate the inside temp to be 70 centigrade. Upon first start the vent temps kept going down (got to -1.5) and I thought I was onto something, then they gradually increased to 8-9, the next day the best I could get was 12-14 degrees. Maybe need to locate the evaporator temp sensor and attempt a similar modification?

[install monkey]

moisture in the fridge side,or going out on freeze protection ? you need a fridgie to get some gauges on it, if its a new company car get the bugger back under warranty- saves you ripping the dash to bits

[R717]

Hi Charlie

I'm not saying I'd like 5 degrees constantly, just maybe a little longer than the HVAC currently decides. As you've mentioned the vehicle interior absorbs so much heat that as the HVAC throttles off to around 15 degrees I'm fighting a losing battle. I know the system has the capacity as on a recently hot day (40 centigrade) with the car in the sun parked for a couple of hours the vent temperatues went to -1.5 for a short time before easing back to around 9 degrees. Perhaps I'll try bypassing the in-car temperature sensor with a resistor of value which would indicate to the HVAC that the in-car temp is a constant say 40 centigrade and see what happens to the vent temperatures then? I think the evap sensor may be difficult to get to, as is the sun load sensor. Any other ideas would be appreciated, especially as I just heard the forcast for today and we're heading for 39 degrees again!!!

OMG.....what a monstrosity !! In car temp sensor, evap sensor, ambient temp sensor, sun load sensor, sensor this, sensor that, computer to second guess the comfort level of the occupants............Automotive HVAC really only needs the biological air conditioning controller.....YOU. After all you are already driving the car, switching the a/c on/off is no harder than than switching on the wipers.

If you are hot put the a/c on if you are cold turn it off.

Given the large number of ever changing variables in a automobile including the personal feelings of the driver / passengers, how can a programmer work out a program for a computer to virtually "read your mind" and control automotive air conditioning system to accurately provide the temp you want at any particular time ??

Many cars a/c don't have the capacity to cope on a hot day even running flat out but to then be burdened with numerous complex control inputs really makes the job much harder. The compressor in my car needs to run constantly to achieve proper functioning.

I have a old Ford that suffers the same problem as your Holden, ie: vent temps not really cold enough on the occasions you really want it, and let's face it there is nothing worse than a car a/c that blows lukewarm air while burning up petrol and producing tremendous underbonnet temperatures, i decided to eliminate what i call all "the second guessing controls" such as the de-icing switch and the thermostat, i am the new de-icing and thermostatic control via the on/off switch.

This allowed the system to get a go on and get the evap temp pulled down to a stable level. I have never found the need to de-ice, there is so much heat in a car coming in from every direction ice formation is just non existent. Maybe on a cold rainy day ? but then you probably wont be using the a/c ?

I don't know how hard it would be to eliminate the superfluous controls on a more modern car but a simple on/off switch does me. I don't like a designer in a office somewhere deciding how hot or cold i am.!!

[mikeref]

The only thing we need in Australian vehicles on hot days is a simple thermostat for temperature control.

Has anyone here heard of a computer controlled hot water valve to regulate engine water temperature to the heater coil, AND using the air-con to soften the air temperature coming out the air vents when we ask for heating on cold mornings?...NO..

[R717]

Have to find the evaporator temperature sensor first, any one know exactly where it's located?

I found some info that may help you out.

Evaporator Temperature Control
As the A/C system uses a Denso variable stroke and "clutchless" compressor that utilises an ECVD (electronic control valve) operated via the HVAC Control Module to increase or decrease the crankcase pressure in the compressor, which then alters the compressor output (displacement). The evaporator temperature sensor has no bearing on the cycling of the compressor as there is no direct or indirect electrical connection to the compressor from the vehicles wiring harness, as no clutch exists on the compressor. The compressor is operating constantly when the engine is operating, only the compressor output is adjusted. The evaporator temperature sensor is located in the lower section of the HVAC in the air intake stream after the evaporator and is used for sensing the incoming air temperature after the evaporator into the HVAC, to be used as part of the output calculation by the evaporator temperature sensor values are also required to operate the ECVD (electronic control valve) of the compressor to alter the stroke (displacement / output) for the A/C system.

I found this on: http://www.carmodder.com/ve-factory-...on-t13637.html