School me on a/c condenser locations, multiple units

[TRE Cup]

There have been all sorts of threads regarding upgrading a/c systems on the G and older series 911s. Electric, dual condensers, fans, etc etc.
Porsche thought it best on the early 911s to put a small front condenser with fan under the trunk and then one over the engine on the rear lid. This persisted till the end of 1989.
Griffiths, and others have upgraded the factory system with single or dual left rear fender condensers. Some people kept the front tub condenser in the loop, while others have removed it so there is "only" three with these set ups.

So if we keep the rear lid condenser, what if we have space and plenty of air for for a large parallel flow condenser in a 74 RSR front bumper ? The external oil cooler is still in the right front fender, so a large condenser (with two suck through fans) can be fitted with no obstruction of "pre heat" ;-) .
What are the pros and cons of having the rear lid and front mounted condenser operating in this manner ?

Appreciate your input
Dave

[GH85Carrera]

The big limiting factor for the 911 AC system is the lack of condenser volume. The two factory condensers just can't keep up.

I did a lot of reading, and looked at different systems on the market back when I was ready to have some good AC. I live in a part of the country that often gets to high 90s or even to the 100s. I also make road trips, and I drive across country in the summer.

I just maned up, and went for the Griffiths 4 condenser system. I added the two condensers in the rear fender, replaced all the hoses (a vital step) and of course a new receiver-dryer and a new evaporator. Later I upgraded to the hurricane blower, and the variable speed fan controller, and temp controller. I even added the extra vents inside since my 85 has the tiny vents on the sides of the dash.

It simply works, and it has worked since 2007 when I did the majority of the work. I have been in Savannah GA in AUGUST, and I heard my wife say "I am cold, turn the temperature up please" I almost got out and did a happy dance. I have been in Key West in late July and my only problem was my sun glasses kept fogging up when I stepped out of the car.

Driving due west, on I-40 in the afternoon with the sun shining right in my face, warming my chest, the dash was so hot I could not hold my hand on it, it was 100+ outside, and I had to turn the temp up as it was too cold after driving for hours.

The ONLY parts of my system left stock is the front and rear condenser. Every other part, except some brackets and the dash vents are replaced.

I can't speak at all about the other systems as I have no first hand knowledge about them.

[TRE Cup]

Thank you Glenn
From your experiences with your system, I think we will move forward with a large condenser that will fit the IROC bumper. That should solve the needs on this particular project.
The plan all along was to get the hurricane blower, the better evaporator core, new txv valve, barrier hoses and receiver drier.
It will be interesting to hear other 911 owners experiences using an aftermarket large front condenser like we intend on doing

[GH85Carrera]

The large front condenser will be nice when moving along, but not much help when going slow or at a stop.

For my 1986 El Camino the AC kicks butt. Except when stopped. The cool air gets warm fast.

Or it did, I added a large electric fan in front of the condenser. Then I wired in a dual relay that I figured out how to have the fan ONLY come on if the compressor is running, and if the brake lights are on. That way it does not try to run in the 70+ MPH wind on the interstate, or when not needed.

It made a huge difference for coming to a stop at a red light.

[Mocker]

You might want to make sure you have the room in the front center--I doubt you'll be able to fit two fans in there. That's why the Griffith kit puts them in the left rear wheel well.

Full disclosure: I am very satisfied with the mac-daddy Griffith upgrade in my 79 930.

[Nditiz1]

Is the Griffiths 4 condenser setup all new equipment, meaning compressor, dryer, evaporator, blower OR does it just add 4 condensors to your existing setup. Are 4 needed? Has anyone actually done just 2 with all new stuff to see how it works?

[Michael7810]

I live in Phoenix and have the Griffith system with only 2 condensers. I had intended to use 4 condensers but when I ordered the system last December I was told the 2 auxiliary condensers were unavailable due to supply issues and it could be 6 months to 2 years before they would be available. I talked to a guy at Patrick Motor Sports and he said they don't use 4 condensers (and that was confirmed by Griffith). I replaced everything except the rear condenser. The car is not my daily driver but I have had it out several times in 100+ weather and it works satisfactorily. I think it would struggle if the car was sitting in the sun for a couple hours and then I was stuck in traffic...but for driving around town and certainly on the freeway it does an adequate job. I think the 86+ cars would do much better with larger dash vents. I'm happy with it as is and won't bother to add the aux condensers when(ever) they are available.

[blucille]

I too have the griff 4 condenser system with two condensers and fans in the left rear wheel well.

I’ve had the system installed in my black SC for 8 years without a single hiccup or recharge. And the system will freeze me out on the hottest and most humid days the New York metro area sends me.

The system performs flawlessly. I very seldom turn the fan or thermostat past 60%.

[kuehl]

Originally Posted by TRE Cup

So if we keep the rear lid condenser, what if we have space and plenty of air for for a large parallel flow condenser in a 74 RSR front bumper ?

What is the front condenser's length and height that will be exposed (facing forward)?

[RSTarga]

Originally Posted by TRE Cup

There have been all sorts of threads regarding upgrading a/c systems on the G and older series 911s. Electric, dual condensers, fans, etc etc.
Porsche thought it best on the early 911s to put a small front condenser with fan under the trunk and then one over the engine on the rear lid. This persisted till the end of 1989.
Griffiths, and others have upgraded the factory system with single or dual left rear fender condensers. Some people kept the front tub condenser in the loop, while others have removed it so there is "only" three with these set ups.

So if we keep the rear lid condenser, what if we have space and plenty of air for for a large parallel flow condenser in a 74 RSR front bumper ? The external oil cooler is still in the right front fender, so a large condenser (with two suck through fans) can be fitted with no obstruction of "pre heat" ;-) .
What are the pros and cons of having the rear lid and front mounted condenser operating in this manner ?

Appreciate your input
Dave

I have a 73 Targa with the over the engine condenser and the very dinky front condenser mounted in an RS front spoiler in place of an oil cooler. I should also mention I have a ducktail. Sanden style compressor, R12.
It was 98 yesterday with 90% humidity in South Texas. I drove 150 miles and my vent temps were under 50 degrees. I had to turn both the thermostat and the fan down as it was too cold.
I think the ducktail increases the efficiency of the rear condenser, and even this small front condenser in direct airflow make it work. I will say that the effectiveness is reduced while standing still for a period of time in high temps, so a front fan would be a good idea if you can fit one in.

[Nditiz1]

Originally Posted by RSTarga

I have a 73 Targa with the over the engine condenser and the very dinky front condenser mounted in an RS front spoiler in place of an oil cooler. I should also mention I have a ducktail. Sanden style compressor, R12.
It was 98 yesterday with 90% humidity in South Texas. I drove 150 miles and my vent temps were under 50 degrees. I had to turn both the thermostat and the fan down as it was too cold.
I think the ducktail increases the efficiency of the rear condenser, and even this small front condenser in direct airflow make it work. I will say that the effectiveness is reduced while standing still for a period of time in high temps, so a front fan would be a good idea if you can fit one in.

So is this just the factory setup? Do you have the under dash blower? Did you leave a garage where your car was at a cool 75-80F before heading out into the sun? Did you ever stop during the 150 mile trip and let the car get heat soaked for an hour or so? I ask because several AC owners throw out these claims about how effective their system is, but don't provide more details of the setup/conditions. I do appreciate you including the temps/humidity.

[GH85Carrera]

Originally Posted by Nditiz1

So is this just the factory setup? Do you have the under dash blower? Did you leave a garage where your car was at a cool 75-80F before heading out into the sun? Did you ever stop during the 150 mile trip and let the car get heat soaked for an hour or so? I ask because several AC owners throw out these claims about how effective their system is, but don't provide more details of the setup/conditions. I do appreciate you including the temps/humidity.

As I have mentioned in the posts above, I have the 4 condenser system from Griffiths. Read my posts above for what my system is.

When I drove down to Key West, we stopped on one of the bigger keys for seafood lunch. My 85 911 was parked in the full sun, on a very sunny day, in July, in the Florida keys for the 1.5 hour lunch stop. We had driven there from Boca Raton, so the engine was good and hot, and then the interior was nice and toasty from the sun.

We hopped in, and within 60 seconds I could feel cool air pumping in. Within 5 minutes it was comfortable enough, but I left the system at MAX cold for 15 minutes until we got to a spot to take some pictures. When we stepped from the car our glasses fogged up instantly from the humidity and heat of the keys.

We drove to Key west, and I handed my brother my camera all set up and ready to fire.



We were completely comfortable for the entire trip.


This is my car in front of Little Round Top at Gettysburg, PA.


Laguna Seca was a really pleasant day, and no AC was needed. The trip to California and back home through beauty spots like Needles, CA where it was 118 degrees (not heat index) tested the AC system. I never broke a sweat, but I was not getting cold.

Just talk to Charlie Griffith. He can set you up with what will fit your needs.

[RSTarga]

Originally Posted by Nditiz1

So is this just the factory setup? Do you have the under dash blower? Did you leave a garage where your car was at a cool 75-80F before heading out into the sun? Did you ever stop during the 150 mile trip and let the car get heat soaked for an hour or so? I ask because several AC owners throw out these claims about how effective their system is, but don't provide more details of the setup/conditions. I do appreciate you including the temps/humidity.

My car has the VWof America dealer installed A/C. Vents under dash vents , blower evaporater in the smugglers box. The front condenser is the factory tube and fin but standing up on the front RS spoiler.
I stopped for lunch with the car in the sun and got back on the highway, cooled down within a couple of miles. I've had the same setup for 35 years in Texas. When I had the stock engine lid and no front condenser it really had a hard time keeping up, even on the highway. Once I fitted the duck and the front RS spoiler with the upright condenser it was a game changer. The Sanden compressor also was a great improvement. It's a Targa with the black roof too. It's all about direct airflow over the condensers.
Probably would not work as well on R134. Maybe I'ld have to use a larger front condenser, there is room, no room for fans though. I will clarify that if I am caught in a traffic jam in 100 degrees it definitely loses efficiency.No airflow....

[fintstone]

This is a pretty well documented build.

Obligatory 32F AC vent image

[Jonny H]

Originally Posted by TRE Cup

There have been all sorts of threads regarding upgrading a/c systems on the G and older series 911s. Electric, dual condensers, fans, etc etc.
Porsche thought it best on the early 911s to put a small front condenser with fan under the trunk and then one over the engine on the rear lid. This persisted till the end of 1989.
Griffiths, and others have upgraded the factory system with single or dual left rear fender condensers. Some people kept the front tub condenser in the loop, while others have removed it so there is "only" three with these set ups.

So if we keep the rear lid condenser, what if we have space and plenty of air for for a large parallel flow condenser in a 74 RSR front bumper ? The external oil cooler is still in the right front fender, so a large condenser (with two suck through fans) can be fitted with no obstruction of "pre heat" ;-) .
What are the pros and cons of having the rear lid and front mounted condenser operating in this manner ?

Appreciate your input
Dave

For the RSR, use the central opening for your oil cooler and put a condenser under each headlight. That way you are not having any issues with pre heat of the oil cooler and you also have no heat soak on the condensers either (which you will get from mounting above the engine). Best of both worlds.

You do NOT need any ram air if you fully seal the fan shroud as we do with our condensers (which are from the 997).

Each 997 condenser has a heat load rating of 5kW giving a total load of 10kW. Given that the evaporator is around 4-5kW plus a little extra for rejection of compression heat, I can't see the point in adding any more condenser real estate.

[hannu_911]

It would be interesting to see how much additional temperature drop one would get from the 2nd, 3rd and 4th condensers.

Here is what I get from my single condenser setup.
88F Ambient
52F Center vents
199F Compressor out (measured on the surface of the barrier hose)
127F Evaporator in (measured on the surface of the barrier hose)
63F Compressor in
Measured with infrared thermometer on the surface of the barrier hose.
I have one 991 turbo condenser behind the left rear wheel in my Classic retrofit setup, no front condensers.

[GH85Carrera]

Originally Posted by hannu_911

It would be interesting to see how much additional temperature drop one would get from the 2nd, 3rd and 4th condensers.

Here is what I get from my single condenser setup.
88F Ambient
52F Center vents
199F Compressor out (measured on the surface of the barrier hose)
127F Evaporator in (measured on the surface of the barrier hose)
63F Compressor in
Measured with infrared thermometer on the surface of the barrier hose.
I have one 991 turbo condenser behind the left rear wheel in my Classic retrofit setup, no front condensers.

I can get 40 degree air blowing out my vents with the hurricane blower blasting out max volume air in 90+ degree weather, and my return line to the compressor is cold enough to make frost on the pipe when it is high 80s and low 90s. Above low 90s the line is just wet from condensation, no frost. Even on 100 degree days on a long drive, the return line to the compress is wet with condensation.

I have 4 condensers with the Griffiths system. I can say cool in 100+ degree temps.

[Nditiz1]

I'm not positive on the science of needing additional condensers (more than 2) I am positive that the hurricane blower against the evaporator is what is making the difference between CR and griffiths. If I can't figure out how to squeeze more air flow out of the CR unit I might make a jump.

[hannu_911]

Originally Posted by GH85Carrera

I have 4 condensers with the Griffiths system.

Glen - it would be very interesting to know what is the temperature of the
-compressor output
-1st condenser output
-2nd condenser output
-3rd condenser output
-4th condenser output
on your system. So how each condenser contributes to your system performance.

[GH85Carrera]

Wow, that would be a real pain to measure. The two fender condensers are up in the fender in front and behind the rear tire. The only condenser that is easy to get to is the one over the engine. The front condenser is hidden under a cover. I can tell you that the heat from the rear condenser is reduced, and my engine temps dropped after installing the two additional condensers. No other change except the new condensers and engine temps dropped.

Charlie Griffith did a lot of design and development on his system. He likely has that information, but I have no idea if he will share. I live in a part of the USA that gets HOT in summer. It is 95 degrees here right now, and the heat index is 106. I told Charlie I wanted max performance for hot days. Every single part of my AC system has been replaced with the exception of the front condenser, and the rear condenser. That of course excludes brackets and clamps and parts of the system that are not under pressure with the refrigerant.

To get the full cold air under extreme heat the lack of condenser capacity is the 911s AC system biggest weakness.

One story from the days when the Carrera was new, Oklahoma City used to be the home of Tech sessions. We had a factory speaker from Germany come talk to us every year. As I remember it was Tony Lapine that came in the mid 1980s and discussed his design work. As a typical German, he wanted to drive Rt-66 and he arranged for Porsche AG to have a new 911 ready for him to drive to California on Rt-66. He made his trip, and when he returned to Germany he went to Peter Schutz's office and they called in the two guys in charge of AC for the 911. They told the guys they were going to be sent to the US, and they get to drive a new 911 from Oklahoma to California.

They returned and reported back and said sir, the AC system in our cars really suck, and Peter put them to work designing a new AC system that works. It was incorporated in the 964 and those cars and later 911s have decent AC. Check out a 964 AC system, and the condenser capacity. From what I understand they have decent AC.