A/C source/question/Is there one...

[e p slick]

For a number of reasons I do not want to run a belt drive A/C compressor in the engine bay (1979 930). Does anyone know of an electrically powered compressor one could position in the front trunk?

Thanks

EPS

[911pcars]

Hybrid vehicles typically use an electric A/C compressor. Check compressor power requirements first.

BTW, Howard Hughs had an electric A/C system installed in his '49 (?) Buick. He being the ultimate hypochondriac, he wanted cool, filtered air even when the engine was OFF.

Sherwood

[Jim Sims]

http://www.masterflux.com/userimages/Tecumseh%20Product%20Highlights%20042809.pdf

When run in a 12-volt system the smaller units require around 50 amps therefore an electrical system upgrade will probably be required. Higher capacity alternator (or a second alternator), perhaps an additional battery and larger gauge wiring running fore-aft will be required for a unit of adequate capacity. Note the biggest issue in the 911 body style is where to put the condensers.

These DC units are probably the "wave of the future" for automotive HVAC (along with DC motor powered coolant and power steering pumps) but the electrical system voltages will have to be upgraded for optimum efficiency - this presents safety problems if the voltages become high enough to cause lethal electrocution.
Perhaps a dual voltage system will be adopted to reduce this hazard.

[kuehl]

We investigated a system for a few clients, long discussions with the the company Jim mentioned and others. The challenge we determined was getting enough flow to meet the BTU requirements of a typical 911 based on what products are available today, that led into power requirements and so forth (frequency and voltage of available product in the market). Condenser placement is not a difficult issue. If you think of weight, system complexity, a belt drive pump is still the easiest and most economical solution at the moment.

[darthracing]

Originally Posted by kuehl

We investigated a system for a few clients, long discussions with the the company Jim mentioned and others. The challenge we determined was getting enough flow to meet the BTU requirements of a typical 911 based on what products are available today, that led into power requirements and so forth (frequency and voltage of available product in the market). Condenser placement is not a difficult issue. If you think of weight, system complexity, a belt drive pump is still the easiest and most economical solution at the moment.

Glad I checked the forum on this one - I've been hoping for en efficient complete replacement for my 911 AC rather than "repairing" a sad design...

-T

[tctnd]

Here's my solution. I didn't like the look of the compressor and additional belt hanging out the back so I mounted a tiny Sanden clone where the MFI pump would have gone if it had one, and ran a drive from the alternator to a multi groove pulley to turn it. I don't recommend this unless you are semi-obsessed as its a lot of work for a dubious benefit. My rational was to move the CG forward but it was really driven by a personality defect.
regards,
Phil

[kuehl]

"efficient": can be in the eyes of the beholder: cost vs. payoff.


tctnd ... . nice work!

Originally Posted by darthracing

Glad I checked the forum on this one - I've been hoping for en efficient complete replacement for my 911 AC rather than "repairing" a sad design...

-T

[wwest]

Originally Posted by Jim Sims

http://www.masterflux.com/userimages/Tecumseh%20Product%20Highlights%20042809.pdf

When run in a 12-volt system the smaller units require around 50 amps therefore an electrical system upgrade will probably be required. Higher capacity alternator (or a second alternator), perhaps an additional battery and larger gauge wiring running fore-aft will be required for a unit of adequate capacity. Note the biggest issue in the 911 body style is where to put the condensers.

These DC units are probably the "wave of the future" for automotive HVAC (along with DC motor powered coolant and power steering pumps) but the electrical system voltages will have to be upgraded for optimum efficiency - this presents safety problems if the voltages become high enough to cause lethal electrocution.
Perhaps a dual voltage system will be adopted to reduce this hazard.

"..this presents safety problems..."

No, not if the DC-DC inverter, up-convertor, is integrated, incapsulated, within the same assembly as the high voltage inverter generating the A/C multiphase voltages driving the brushless "DC" permanent magnet rotor motor

"..12-volt system...require around 50 amps..."

600 watts...I don't think so, 600 watts would be only ~1800 BTU of direct electric heat transfer and only ~5400 BTUs, PEAK, if amplified via an A/C refrigerant heat transfer system.

The 2010 Prius electric A/C has a PEAK BTU capability of ~15,000 BTU, just over a ton of peak cooling capability.

But the true question becomes.....how much of that peak capability is needed once the cabin has been initially cooled down..."

First, toss out the A/C's (manual and auto) "reheat/remix" airflow path that has become pretty much standard these days. Block ALL engine coolant flow to the heater core during A/C use.

And remember that an electrically driven A/C compressor's RPM can be varied, reduced, to whatever level will just barely keep the cabin at/near your comfort level.

Bottom line is that adoption of an electrically driven A/C compressor could/might result in less overall engine loading than a engine direct driven compressor.

My '01 C4 has a switch mounted inside the glove box that I use to disable the A/C compressor except when I have a need, typically summer months only, for actual cooling. I also have a manual shutoff valve in series with the engine coolant flow to the heater core that I close when the A/C is enabled.

More efficient A/C cooling and improved FE.

[wwest]

Originally Posted by tctnd

Here's my solution. I didn't like the look of the compressor and additional belt hanging out the back so I mounted a tiny Sanden clone where the MFI pump would have gone if it had one, and ran a drive from the alternator to a multi groove pulley to turn it. I don't recommend this unless you are semi-obsessed as its a lot of work for a dubious benefit. My rational was to move the CG forward but it was really driven by a personality defect.
regards,
Phil

Why not convert that belt drive to a CVT V-belt, Toyota PSD, type higher ratio drive system?

Or even a PSD type CVT...?

No clutch (weight) and a smaller, lower displacment volume (weight) compressor, and vary the RPM of the compressor as a function of cooling level required.

[kuehl]

The 911/930 through 1989 (pre 964) are all full recirculation (no outside air or heater air mixed with the ac air), you can't get more efficient than that in terms of what you want to cool; other than if the outside ambient is cooler than than the cockpit then by all means open the windows until temps equalize (humidity excluded for the comment) and then turn on the air conditioning.

Varying the compressor rpm (or rate of output) was accomplished many years ago with 'variable displacement wobble plate piston compressors; this accomplished with a mechanical signal. Later developments along the same lines were done with scroll units and are employed today in 'cars' as well as stationary units (truck cabs for overnight parking for example). However, for our currently owned or driven generation models this is done rather simply by the evaporator core's thermostat signal cycling the compressor on and off; mechanically (pre 964) or electronically (964 onward).

The challenge for our driven models if you want to develop or transfer over current technology is heat gain inside the cockpit. The latest generation out there for people cars is 3.4 btu or 1 kw (not enough). Assuming 1 ton will remove
720000 k/cal heat, latent heat that is, so coat those windows boys.

[wwest]

"..through 1989 (Pre-964) are all full recirculation...."

That's what I always thought also until I needed to work on our '88 Carrera's A/C. If you look carefully at the cabin to evaporator intake duct, the one the dropping resistors are mounted inside for cooling, you will see an alternate air entry path, FRESH air entry path.

"..many years ago...wobble plate...."

A/C compressors using that very same technique were introduced (re-introduced..??) within the Toyota product line just in the past 5-7 years.

"..current generation.."

The 996/997 series has two design flaws in the A/C system, three if you count the wasteful, needless, and often UNSAFE operation of the A/C compressor for other than cooling.

1. Once the cabin temperature declines to, or nearly to, the temperature setpoint, the system automatically opens all air outflow paths, dash, footwell AND windshield defrost/defog/demist ducts, and then lowers the blower speed accordingly. This mode is generally less discomforting, NO "RUSH", RUSHING, of the entire mass of cooling air directly to the face and upper body. But two problems arise, loss of cooling capacity on/through the windshield glass and inadvertent cooling of the windshield exterior surface often resulting in condensation formation on the windshield. Since that condensation may not be noticed right away, say in the early evening shortly after dusk, or the onset might be vertially instant and vistually blinding, that represents a potential for an accident cause.

2. The reheat/remix cycle is simply nothing less than stupid and results in additional fuel consumption.

[kuehl]

"That's what I always thought also until I needed to work on our '88 Carrera's A/C. If you look carefully at the cabin to evaporator intake duct, the one the dropping resistors are mounted inside for cooling, you will see an alternate air entry path, FRESH air entry path.
"
hmmmmm.... I don't think so. There are 2 air intakes from the cabin to the evaporator, each being under the foot boards. The intake you have mentioned, under the RH side foot board (passenger side on this side of the pond) containing the OEM fan speed shunt resistor pack mounted in the plastic trapezoid plenum, does not allow (when properly sealed) outside air to enter either the cabin or the evaporator. All pre 964 factory air and aftermarket models are all 100% recirculation. Stop on over my shop and I'll show you how to R&R a 911 evap in 40 minutes or less; bring the Becks.

"A/C compressors using that very same technique were introduced (re-introduced..??) within the Toyota product line just in the past 5-7 years."
I was mentioning the variable displacement wobble plate as opposed to fixed displacement as being a method of reducing compressor load (energy requirements).

'However, for our currently owned or driven generation models' ... this means 911 and 930 in the paragraph. Tis is an air cooled forum?

I agree, a cold windshield on hot humid day is a pita for sure when the condensation greets you. Seems to happen on plenty of other brands, new and old. That's why we have defrosters and windshield wipers.

As far as design flaws? All cars have them! Its us Monday Night quarter backs that enjoy fix'n and improvising um.

[wwest]

The newer Toyota's use wobble plates within the A/C compressor to modify displacement volume.

Now I have to go back and dig into my '88 since I'm pretty, but not certain, of what I saw. It's in the process of getting bi-xenon HID bulb retrofit/upgrade, replace the 9004, at the moment.

[kuehl]

Most piston compressors have 'wobble' plates, such as Sanden 507, Nippon 10P15C and E and whole magilla of other brands and models; except the old York crank shaft designs.

A "wobble" plate (sometimes called a swash plate), attached to the shaft, moves the piston(s) back and forth. In a variable displacement piston compressor by the angle of the plate you can change the length of stroke; hence a 'variable displacement'. Fixed displacement compressors, such as what we find on the 84+ 911, and the 964/993 models, have swash plates.

You don't have to dig into your 911 to see if it has outside air entering the RH intake plenum. Trust me (I'll never raise your taxes!).

So, you gonna blind us all know with those funky HID's? Hope you did not go over 5Kelvin.

[wwest]

Okay, so the new Toyota has an adjustable wobble for the swash plate, just like helucopters.

Sometimes taxes do have to be raised, more, increased, government services,....more taxing.

4300K

[kuehl]

4300K ! Thank you for not blinding me West.

We don't need more government services, this is the 21st century. Let's start off by deleting the Congress and Senate.... where is the delete tab ?