A/C "recirculate" mode??

[chrisbruck]

So is there any sort of "recirculate" mode to the stock A/C system like a "normal" car has or does it only blow cool air in the cabin from the outside?

Mine works pretty well but I can 't seem to tell and it would be nice to pull some humid air out of the cabin while blowing dry air back in.

[javadog]

It's always recirculating air. It pulls it into the evaporator from a hole under the passenger floor board.

JR

[chrisbruck]

Ah, cool! (well, sort of "cool"). Good to know that.

[OttawaDave]

Here's a related question then: how does that other knob work on the ac controls? I had thought it blended in outside (or otherwise warmer) air...?

[wwest]

If the cabin is "super-heated", triple black and setting out in the Texas sun all day, you may want to run the fresh air intale blower for the first few minutes of operation, or/and with the windows down.

[kuehl]

If you want to cool the car down quickly simply open all the windows and sun roof if you have one; ie. if the outside air temp is 99F and the cockpit is 125F, the outside world can suck the heat out of the car quicker than the fresh air cooling fan. So....., open the windows, start the car, drive down the road, and when the cockpit feels as cool as it can get then turn on the ac (turn both thermostat and evap blower knobs fully clockwise; this will clear out the residual heat soaked vents quickly) and when the vents start to feel cool then you can start closing up the windows and adjusting the thermostat and fan speed to your desire.

The Mr. Ice Project

[javadog]

Originally Posted by OttawaDave

Here's a related question then: how does that other knob work on the ac controls? I had thought it blended in outside (or otherwise warmer) air...?

You have two knobs. One controls the fan speed and the other is essentially a thermostat. It determines how much the compressor cycles on and off, thus determining the temperature. There's no air blending in a 911 A/C system of that era. Outside air is available via the top black lever on the dash. The middle black lever directs the frsh air to the dash vents, or footwell vents, or both. It's a separate path from the A/C air.

JR

[wwest]

Originally Posted by kuehl

If you want to cool the car down quickly simply open all the windows and sun roof if you have one; ie. if the outside air temp is 99F and the cockpit is 125F, the outside world can suck the heat out of the car quicker than the fresh air cooling fan. So....., open the windows, start the car, drive down the road, and when the cockpit feels as cool as it can get then turn on the ac (turn both thermostat and evap blower knobs fully clockwise; this will clear out the residual heat soaked vents quickly) and when the vents start to feel cool then you can start closing up the windows and adjusting the thermostat and fan speed to your desire.

The Mr. Ice Project

The only revisional suggestion I would make would be to turn on the A/C IMMEDIATELY, no good reason to delay until the cabin atmosphere and surface "surround" is cooled down. Get that evaporator cooled down, CHILLED, asap.

[wwest]

Originally Posted by javadog

You have two knobs. One controls the fan speed and the other is essentially a thermostat. It determines how much the compressor cycles on and off, thus determining the temperature. There's no air blending in a 911 A/C system of that era. Outside air is available via the top black lever on the dash. The middle black lever directs the frsh air to the dash vents, or footwell vents, or both. It's a separate path from the A/C air.

JR

Personally I would recommend keeping the thermostat setting at maximum cooling and use, at least initially, the blower speed to modulate, moderate, the cabin temperature, comfort level. Dehumidification of the cabin atmosphere is a big aspect of human comfort level and that can be best accomplished with the COLDEST evaporator surface temperature, ~34F, feasible.

[javadog]

I never ran mine at less than full blast on both knobs. But then again, I live where it's hot...

JR

[kuehl]

Originally Posted by wwest

The only revisional suggestion I would make would be to turn on the A/C IMMEDIATELY, no good reason to delay until the cabin atmosphere and surface "surround" is cooled down. Get that evaporator cooled down, CHILLED, asap.

Your 'suggested revision' has been REJECTED ! It defies the laws of physics.

Since outside ambient air cools a cockpit sooner than the ac system could
its not logical to load up the evaporator with hot cabin air.

[SilberUrS6]

Originally Posted by kuehl

Your 'suggested revision' has been REJECTED ! It defies the laws of physics.

Since outside ambient air cools a cockpit sooner than the ac system could
its not logical to load up the evaporator with hot cabin air.

But, what if you are running decklid fans? *Surely* that will help.

[wwest]

Every Lexus I have owned, still own, has had an automatic climate control system that in "this" situation, close up, hot sun, super-heated interior, will immediately go into full A/C blower and start fully cooling, CHILLING (34F "target") the A/C evaporator, air reheat/remix door fully closed, and place the system in full recirculate.

My "job" is to, as quickly as I can, place the system in "fresh" while simultaneously lowering the rear windows slightly. Within a few minutes I raise the windows and if I wish maximum efficiency from the A/C I switch the system back into recirculate mode.

So, yes, there will be a minute or so wherein the evaporator cooling system will be inordinantly burdened with the over-heated airflow but it will also be helpful in more quickly reducing the temperature of the cabin atmosphere.

[wwest]

Originally Posted by kuehl

Your 'suggested revision' has been REJECTED ! It defies the laws of physics.

Since outside ambient air cools a cockpit sooner than the ac system could
its not logical to load up the evaporator with hot cabin air.

But it is perfectly logical, and in perfect alignment with the laws of physics, to make simultaneous use of BOTH in order to cool the cabin down quicker than ether one alone.

[kuehl]

Originally Posted by wwest

But it is perfectly logical, and in perfect alignment with the laws of physics, to make simultaneous use of BOTH in order to cool the cabin down quicker than ether one alone.

"laws of physics'... well Wild West let's hear the law of physics,
Please quote the scholars:
Sir Benjamin Thompson
Sadi Carnot
Rudolf Clausius
Ralph H. Fowler
.... we are waiting patiently, all of us... lol

[wwest]

I really do enjoy leaving the less educated "hanging"!

[kuehl]

Originally Posted by OttawaDave

Here's a related question then: how does that other knob work on the ac controls? I had thought it blended in outside (or otherwise warmer) air...?

With regard to the thermostat (LH knob), go here:
AIR CONDITIONING HELP
and review "The AC Temperature Switch - An example in detail with a typical 911 Porsche"

[wwest]

Originally Posted by kuehl

With regard to the thermostat (LH knob), go here:
AIR CONDITIONING HELP
and review "The AC Temperature Switch - An example in detail with a typical 911 Porsche"

Considering the horribly misleading section about the use of the sight ("site") glass at the linked site I'm not sure anything there should be trusted.

What I expect to see in the sign glass as the compressor starts up is "clear", then a brief transition to bubbles, then clear again as the transition to liquid refrigerant occurs.

[wwest]

Originally Posted by kuehl

"laws of physics'... well Wild West let's hear the law of physics,
Please quote the scholars:
Sir Benjamin Thompson
Sadi Carnot
Rudolf Clausius
Ralph H. Fowler
.... we are waiting patiently, all of us... lol

Sorry for the poor, in your face, initial response but I just can't even imagine how or why using both cooling resources simultaneously doesn't get you to the desired cabin atmosphere sooner that either one alone.

[SilberUrS6]

Originally Posted by wwest

I really do enjoy leaving the less educated "hanging"!

Which, by the strangest of coincidences, looks EXACTLY like being uneducated oneself.

The mental image I get is my physical chemistry professor in full facepalm.