Stock evaporator performance ?

[azhodge]

I have seen some really amazing numbers (temperatures) from folks who have conducted various levels of upgrades to their AC Systems. What I would like to know, is what is the best I can expect if regardless of whatever else I upgrade, I stay with the stock evaporator? Or maybe stay with the stock evap and put in a fresh TXV ??

[Bob Kontak]

This is my experience base. A single point of reference.

Garage queen 89 930 and my 81.

My pal and I worked our natural behinds off flushing, changing o-rings (on his - I had tapered interfaces), re-oiling, new receiver driers and TVX valves. I think he installed the pro-cooler type R/D. Both refreshed with R-12 as I got lucky on ebay and snagged a sealed 30lb. tank of DuPont for a fair price.

Here is the rub. Both of our front condenser fans did not work. Both 55F vent temps in around 85-ish F temps. Tolerable but not chilling.

Guessing the operable fans would have stripped 5F ? His relay was bad (tall one up by the front left light) and my fan turns hard.

That's all I got for you.

[86 911 Targa]

Originally Posted by azhodge

I have seen some really amazing numbers (temperatures) from folks who have conducted various levels of upgrades to their AC Systems. What I would like to know, is what is the best I can expect if regardless of whatever else I upgrade, I stay with the stock evaporator? Or maybe stay with the stock evap and put in a fresh TXV ??

I did install a Rennaire Hi-Flow evaporator which has served us well.

Also, re-tuned the temp switch for a 10f hysteresis from the factory 6f setting.

This has reduced evaporator freeze-up in our Hi humidity environment
which has been an ongoing concern.

The rest of the system is factory stock.

If you choose to replace your evaporator,
it should be equipped with the already installed appropriate TXV.

Good luck,

Gerry

[kuehl]

First, you need integrity and reliability. No leaks, the system works when you need it.
This means, if you don't have them, barrier hoses, new o-rings, drier, low high pressure switch. If you have a 86-89 year, the evaporator is prone to leaking because they tried to bond a copper manifold to aluminum tubes and the bond fails over time. Depending upon the mileage on your compressor, as a minimum a seal kit if the internals are good or a new denso.

Second, is performance upgrades. Besides a better evaporator, you need more condenser performance or function. For an Atlanta climate, you need a lot.
The evaporator pulls the heat out the car and the condenser releases it outside.
A rear fender condenser would help; maybe 2 or at least 1 and upgrade your front condenser

You can read about what others experienced with upgrades in the forums; in terms of Griffiths AC products, here:
Customer Comments, Porsche 911 and 930 Air Conditioning Upgrades

[GH85Carrera]

I drove my 85 911 for over 11 years with just the stock system. It was not much fun in the dead of summer.



I finally upgraded my system 9 years ago to a dual Kuehl system and added two condensers and all new hoses and vents. This is a picture I took of my old evaporator. No doubt that was big part of my problem. The drain hole was partially plugged and the entire box was filthy.

Just pulling that old evaporator out and cleaning would have helped but replacing it was the logical thing to do.

As Charlie mentioned, more condenser area is the big step up.

You can peek at the bottom of your evaporator from the passenger compartment. Pull out the carpet and floorboard and the resistor pack. It is pretty easy to take a look and see if it is a gross as mine was.

[wwest]

Originally Posted by azhodge

I have seen some really amazing numbers (temperatures) from folks who have conducted various levels of upgrades to their AC Systems. What I would like to know, is what is the best I can expect if regardless of whatever else I upgrade, I stay with the stock evaporator? Or maybe stay with the stock evap and put in a fresh TXV ??

There is of yet no subjective evidence that upgrading the evaporator and/or the evaporator blower results in an increase in A/C performance ABSENT some method of providing an adequate level of refrigerant condensing efficiency, most especially while idling or driving with consistently low engine RPMs.

The FIRST thing to do on your way to the most comforting A/C is TINT the windows to the greatest level that is legal in your state.

SECOND, find a way to upgrade the condensing efficiency such that the system provides an adequate supply of liquid refrigerant to the TXV in the worse case conditions.

For some of us, that meant simply adding cooling fans to the rear lid condensing such that it could remain productive when the cooling flow provided by the engine fan was not adequate.

For others, in the extreme, it seemed to require upgraded front lip condensers, dual rear fender condensers, along with more efficient evaporators and evaporator blowers.

Care must be taken here since at least one person with the FULL upgrade "boat" freely admits that his A/C comfort level involves sitting in a sub-freezing air stream for hour upon hour.

But I digress..

If, for whatever reason, adding fans to the rear lid condenser doesn't float your boat, then the next best answer is a condenser/fan combination mounted in the front of the driver's side rear fender. You can power the fan via a relay activated by the power to the compressor clutch, as most owners seem to do, or you can use the third element of a trinary pressure switch.

You will need to add a pressure switch regardless of what else, whatever, you choose to do, upgrade, otherwise. There is, literally, no additional cost for a trinary switch vs a binary switch.

Using the trinary switch to control any cooling fan(s) would avoid running the fan(s) when the engine RPM provides a satisfactory level of cooling airflow. And keep in mind that high side pressure doesn't instantly abate with the compressor cutoff. Trinary powered fans would continue to cool the high side until the pressure declines below a set level.

Once you get to the point that liquid refrigerant is available to the TXV in the worse case conditions then it is a quite simple matter to determine if the evaporator/blower combination is efficient enough to "BURN" all the "FUEL" flowing out of the TXV with a FULL heat load.

[SilberUrS6]

Originally Posted by wwest

There is of yet no subjective evidence that upgrading the evaporator and/or the evaporator blower results in an increase in A/C performance

Totally untrue.

Added efficiency in ANY part of the heat exchange system leads to better performance. Including the cabin portion of the system.

Your continued assertion that the choke point of the system is the condensers is false. It has been from the beginning and continues to be false at every repeat. The choke point for this system is the evaporator. It is simply too inefficient to cool the cabin adequately. In fact, upgrading the condensing capacity will have very little effect on cabin temps absent modifications to the evaporator system.

The proof of this is that suction line devices work at all. And they do work, from reports here. If the evaporator was 100% efficient, the suction line devices would have nothing to do. This means there is excess condensing capacity in the stock system.

Straight physics, with evidence. Yet another assertion of your proven false. Will you please stop posting your incorrect and misleadsing drivel? Thank you

[Hoppe]

OK, I think this thread can now end before we begin the constant back and forth that tends to destroy most AC threads. I am a new owner living in NC so the AC threads have been interesting reading...to a point. I need to improve my original AC in the coming year and I have excellent ideas now and have developed a plan to move forward. To continue to beat the dead horse is pretty pointless and I think the OP's question has been answered.

[wwest]

Looks pretty bad, huh..??



But there is no way to know if, or not, the evaporator was doing a perfectly adequate job "as is".

The evaporator in my 1988 Carrera, <100,000 miles, might well look this bad, or possibly even worse.

But the vent temperature and the suction pressure indicate that my evaporator is "Burning" all the "fuel" a wide open TXV, with a adequate supply of liquid refrigerant(***), can provide.

*** 92dF OAT, engine idling (800 RPM), doors wide open, max cooling and blower.

But to be perfectly fair my A/C compressor thermostatic control switch has been calibrated such the evaporator core will not decline to the sub-freezing level.

[SilberUrS6]

Originally Posted by wwest

But there is no way to know if, or not, the evaporator was doing a perfectly adequate job "as is".

Re-read my previous post for the clue you need. Your assertions are false. They continue to be false. You are misleading folks trying to make their systems work, and it's not appropriate for the technical forum for you to do so.

I will repeat: the stock system choke point is at the evaporator. This is so because suction line systems attached to the stock system are reported to work. This would not be so if the evaporator was able to transfer all the energy that the compressor generated through the condensers.

Upgrading the evaporator/evap blower will help the stock system perform better.

[wwest]

Originally Posted by SilberUrS6

Re-read my previous post for the clue you need. Your assertions are false. They continue to be false. You are misleading folks trying to make their systems work, and it's not appropriate for the technical forum for you to do so.

I will repeat: the stock system choke point is at the evaporator.

You and Charlie seem to be at odds on this..

This is so because suction line systems attached to the stock system are reported to work.

Pro-cooler... reported to WORK... ask Charlie....


This would not be so if the evaporator was able to transfer all the energy that the compressor generated through the condensers.

Upgrading the evaporator/evap blower will help the stock system perform better.

You might note that even with best of Charlie's upgrade/retrofit "suite" the suction line ALWAYS sweats in humid environments, even downstream of a "pro-cooler". All that means, even absent "sweating", is that with respect to the OAT, the suction line is always cooler.

And you're supposed to be the most intelligent one of Charlie's disciples....

[wwest]

And then we have this thread. Jump to post 93...

Retroair complete system in my non a/c car

Yes, upgraded evaporator/blower, but a 930 with a sub-standard rear lid condenser/fan capable of supplying adequate refrigerant flow to the TXV?

Reflective condenser surface rejecting radiant heat from the engine/exhaust/catalyst?

If not, then what, how?

EDIT: On second thought... OP has restricted inlet flow to the evaporator plenum, so overall flow volume may be more toward factory than otherwise. Still, IMPRESSIVE results.

[SilberUrS6]

Originally Posted by wwest

You might note that even with best of Charlie's upgrade/retrofit "suite" the suction line ALWAYS sweats in humid environments, even downstream of a "pro-cooler". All that means, even absent "sweating", is that with respect to the OAT, the suction line is always cooler.

And you're supposed to be the most intelligent one of Charlie's disciples....

Moving the baseline. Do you understand what that means?

If I improve efficiency on every component, then overall I can still have a bottleneck in the same location, but that the capacity of the entire system is much higher. Your analytical thinking skills are poor. And Charlie and I have not disagreed on how poor the stock evap is.

[SilberUrS6]

Originally Posted by wwest

Reflective condenser surface rejecting radiant heat from the engine/exhaust/catalyst?

Ahh, yes, another one of your theories that is total crap. The emissivity of aluminum is almost the same whether polished or dull. As in, not a factor. Look up what emissivity means as it applies to radiant energy transfer. Then look up the emissivity of aluminum, and polished aluminum.

Oh, make sure you don't just compare those two numbers. The perfect radiant (or absorptive) black body has an emissivity of 1.00. The difference between aluminum and polished aluminum is REALLY small in comparison to the total possible emissivity, which is in the numerator of the calculation. LOL.

[wwest]

Originally Posted by SilberUrS6

Ahh, yes, another one of your theories that is total crap. The emissivity of aluminum is almost the same whether polished or dull. As in, not a factor. Look up what emissivity means as it applies to radiant energy transfer. Then look up the emissivity of aluminum, and polished aluminum.

Oh, make sure you don't just compare those two numbers. The perfect radiant (or absorptive) black body has an emissivity of 1.00.

The difference between aluminum and polished aluminum is REALLY small in comparison to the total possible emissivity, which is in the numerator of the calculation. LOL.

First, the subject matter is NOT about "emissivity", "out-welling of heat", there is no question that a flat black surface gets the highest marks for that.

But what about "incoming" radiant effects, white, black, silver, or even a chrome or fully mirrored surface??

And the answer is:

http://littleshop.physics.colostate.edu/activities/atmos1/ColorAndCooling.pdf

[SilberUrS6]

Originally Posted by wwest

First, the subject matter is NOT about "emissivity", "out-welling of heat"

In physics, emissivity has a specific definition.

You obviously don't understand it.

And the experiment you posted actually proves my point, if you actually read it.

[wwest]

Originally Posted by SilberUrS6

Moving the baseline. Do you understand what that means?

If I improve efficiency on every component, then overall I can still have a bottleneck in the same location, but that the capacity of the entire system is much higher. Your analytical thinking skills are poor. And Charlie and I have not disagreed on how poor the stock evap is.

Again, NOT the point. The question of Charlie is what is the major "bottleneck" of the factory system.

And yes, even I will agree that most any of the modern aftermarket will out perform the factory evaporator provided the supply of refrigerant is adequate in both cases.

By the by, what is the BTU rating of the factory TXV vs Charlie's.

[SilberUrS6]

Originally Posted by wwest

Again, NOT the point.

In refuting what you claim, it is the point, exactly. When you attempt to change the subject, or switch the discussion around, or redirect it, you are abusing the privilege of posting here. Making wild assertions you cannot prove, making promises you will not keep, all of this makes your posting worthless, and you cheapen every thread in which you participate. You are not helping anyone improve their AC.

[Porsche 2]

If you have not removed your evaporator assembly, take a flash light and mirror and look at the under side of the radiator through the hole under the passenger footboard. Obviously after removing the electrical equipment in the hole. You may find what you see in the picture above.

[Hoppe]

Or not..............another thread high jacked and destroyed.