89 Carrera Budget AC Upgrade....

[Steve Marshall]

I've been messing with the AC on my 86 Carrera the last two summers. New hoses, Griffiths front condenser and evaporator, PFC's in the tail and fender. I feel like I got it dialed in.

In nut shell, air flow, or lack of, over the condensers seemed to have the greatest impact on the system. I was curious what the real world performance would be by just adding electric fans to the rear condenser.

A buddy of mine recently acquired an 89 Carrera with stock AC and we did just that. We got the front condenser fan working and added the fuse. We added two fans to the rear condenser. We evacuated and charged the system it with 46.5 ounces of R134. It's hot AF in Austin right now. I pretty surprised how well it worked. Here are the results:

We charged the system sitting in a super hot unventilated garage.

Ambient temp = 95
Low pressure = 29
HI pressure = 325
Vent temp at idle = 55
Vent temp at 2K rpm = 52

Measured vent temps with a digital probe thermometer on two occasions driving around town. Max speed around 40MPH.

Trip one:

Ambient temp = 93
Vent temp range = 43 to 45

Trip two:

Ambient temp = 102
Vent temp range = 43 to 49

[Ctopher]

Was this a wide body with a wing that the 2 fans were mounted in? If not what size fans were mounted on the rear condenser? Did it still have the heater fan and air box? Got pictures?

[GH85Carrera]

Electric fans on the rear condenser are pretty pointless. The HUGE air sucking fan on the engine sucks a lot of air. A LOT of air. You might see some difference at long stop lights.

That is the real advantage to adding the condensers in the rear fender. The fan on them help a lot and in fact are necessary.

The Griffith's hurricane blower for the condenser blows more air for sure.

So, if you are in traffic at a stop, you might see some minor improvement to AC temps, but you are adding that heat to the engine. As long as you have a fan on the oil cooler you should be OK.

Enjoy the AC, I sure love mine on my 85.

[Discseven]

Steve... I agree with Glen on the volume of air a Porsche engine fan moves---it's impressive. There are specs out there somewhere. I've also stood behind an engine fan while it was being balanced... so I know first hand the hurricane these fans are capable of. My 2 cents here come in two parts. First, I suggest it being better to seal the engine bay so MOST of the air entering the bay does so through the condenser under the draw of the engine's fan. I don't have technical data but would not hesitate to bet the engine's fan in a seal engine bay would out air-flow any mounted fan config.

Secondly, and with due respect to you concerning the ozs charged... am inclined to believe 46.5 being a bit much. I too have a 3 condenser system, albeit with an extra fan in the fender... I run 23 ozs. In 85 dF ambient in Miami, am getting 23 dF at the vent. (Testing done at 2k rpm with fan at low speed, 166 psi HI, 17.5 psi LOW.) I know this vent temp is not practical---it's bittingly cold. And evap is beginning to freeze. Point is... this temp is possible from a 911 AC. Is notably with a digital thermo control with a temp probe near the discharge port in the evap. If your probe is at the center of the evap, you can drop about 10 dF by moving that probe near the discharge port---this is because evap's core operates 10 dF cooler than perimeter by discharge port. (With a temp probe located at core, the evap's not "allowed" to cool to it's potential.) This is provided your thermostat will allow the drop and the system's integrity is in order. In the back of my mind, I can't help but think these stock thermo units are set too conservatively. (And so the reason I developed & tested a digital, Arduino-based control system. Point being to see what level of cold a 911 3-condenser system is capable of.) In other words, with all things set correctly, am not convinced a stock thermostat will allow a 911 AC to perform to its full capacity. With my system as it was, I should have placed the stock thermostat control unit back in to compare. Let's face it, once something is working, it's usually on to something that's not. Good luck with this whatever you do.

[Steve Marshall]

It's not a wide body but it does have a tail. It's equipped with the stock condenser. We just used some fans we had laying around. On the left is a 7" Amazon special and on the right is an old 8" Spal. They clear the heater duct, fan housing, intake manifold and air filter box but it's tight.

[Steve Marshall]

[QUOTE=GH85Carrera;11007831]Electric fans on the rear condenser are pretty pointless.

What I failed to mention was we ran the system for a month without the added fans, but with less freon, and the vent temps were at least 10 degrees warmer. Sure the cooling fan sucks an impressive amount of air, at speed. My experience is the system falls behind at stop lights and in traffic and never catches up. The extra fans are definitely worthwhile in this situation.

I think the performance gain is probably attributable equally to the fans and the freon bump. We shot for the Porsche Service Bulletin amount of 43.5 but missed by a couple ounces.

No doubt all the Griffiths stuff is worthwhile. But for under $ 100 it's worth the effort. If the system produces mid 40's vent temps in 102 ambient, it will probably freeze you out in milder climates.

[Discseven]

Steve... Am not suggesting my way is THE way. Only reporting my findings. I'd agree that condenser performance under an engine fan scenario declines when the engine's idling compared to cruising at higher revs. I'd not go so far to say the system doesn't catch up. I've watched the internal temps in evaporator and know they respond within seconds to any change to the air flow through a condenser. I've also tested water misting a condenser. Adds complexity but that's killer thermal exchange territority. Unnecessary given a system performing well without it.

A near 60 degree delta as you mention is great performance. I'm chatting AC because I like it and, inevitably I learn new things via these discussions.

Griffiths hardware is excellent. So is the man behind it. There's no better install instructions for DIY'ing his hardware and no better support.

[jran76]

This gives me some hope on my 87 in the Texas heat. I have to figure something out....

[Steve Marshall]

Originally Posted by Discseven

Steve... Am not suggesting my way is THE way. Only reporting my findings.

I appreciate your input. I think your way is the way to go. Hell I've got 4 condensers in my 86! And 3 condenser fans! I like messing with the AC. I've also got a 91 VW Westy that I've restored the AC on. Many Pelicans don't care about it but we'd only have about 6 months per year of comfortable driving without it. I'm also a value guy so trying to crack the code without breaking the bank is a challenge I enjoy. (Although this inevitably costs me more in long run).

Arduino is pretty serious tinkering and over my head. What temp differential did you see between the evaporator and vent?

[pavegeno]

Originally Posted by Steve Marshall

I appreciate your input. I think your way is the way to go. Hell I've got 4 condensers in my 86! And 3 condenser fans! I like messing with the AC. I've also got a 91 VW Westy that I've restored the AC on. Many Pelicans don't care about it but we'd only have about 6 months per year of comfortable driving without it. I'm also a value guy so trying to crack the code without breaking the bank is a challenge I enjoy. (Although this inevitably costs me more in long run).

Arduino is pretty serious tinkering and over my head. What temp differential did you see between the evaporator and vent?

Good luck to you.

Living in the south as well, cold a/c is a must. I did the Griff's four condenser system 12 years ago in my 88 Cab. Best money I ever put in the car. Works perfectly with vent temps on highest fan setting in the low 30s. Ten minutes of cool down and then turn the fan and temp setting down even in stop and go traffic with no oil temp issues.

There is a new electric a/c system coming on line you can read about. Choices are good in the market.

[woodyTPA]

I have an 86 carerra and am in process of rebuilding it. I am installing griffiths 4 condensor system. I am using atock evaporator fan with griffiths new evaporator. Any ody using stock evap fan instead of hurricane fan? Cant find parts to retro modify evaporator box to fit hurricane fan.

[pavegeno]

Originally Posted by woodyTPA

I have an 86 carerra and am in process of rebuilding it. I am installing griffiths 4 condensor system. I am using atock evaporator fan with griffiths new evaporator. Any ody using stock evap fan instead of hurricane fan? Cant find parts to retro modify evaporator box to fit hurricane fan.

I sourced all my parts to convert from Aldo at Suncoast Porsche. Big improvement with the Hurricane fan!

[Quicksilver]

Originally Posted by GH85Carrera

Electric fans on the rear condenser are pretty pointless. The HUGE air sucking fan on the engine sucks a lot of air. A LOT of air. You might see some difference at long stop lights.

That is the real advantage to adding the condensers in the rear fender. The fan on them help a lot and in fact are necessary.

The Griffith's hurricane blower for the condenser blows more air for sure.

So, if you are in traffic at a stop, you might see some minor improvement to AC temps, but you are adding that heat to the engine. As long as you have a fan on the oil cooler you should be OK.

Enjoy the AC, I sure love mine on my 85.

Adding an electric fan to pull air into the engine compartment would be pointless because it can't move anywhere as much air as the engine fan.

.. but ...

I've always wanted to try a fan on one side of the grill that blows outwards only when the car is at idle. Blowing outwards would push air outwards at the fan but also pull an equivalent extra quantity of air inwards on the other side of the grill.

[pavegeno]

Drove my 88 911 Cab on a three hour round-trip with my wife for lunch crossing the border into Florida from Alabama.. We like to drive.

Outside Temp 96. Griff's four condenser system with Hurricane fan.

Vent temps in the mid 30s. After first 10 minutes to cool down fan and temp setting reduced to 75% max speed/max cold. I have the variable fan speed controller and hurricane fan. Engine oil temp at or just below first line (90C/194F) during drive. Interior temp in mid 70s and no humidity.

Restaurant was curbside pickup. Parked in the sun for 30 minutes at engine idle while waiting for food and eating. Engine oil temps crept up to one needle width above 90C line. A/c settings stayed in same place. Interior temp stayed in same place. After driving off, engine oil temp dropped back down to the line and then just below.

Best money I ever spent on my car and it's been going strong since 2008.

[kuehl]

Originally Posted by Steve Marshall

We charged the system sitting in a super hot unventilated garage.
46.5 ounces of R134

Ambient temp = 95
Low pressure = 29
HI pressure = 325
Vent temp at idle = 55
Vent temp at 2K rpm = 52

Bogey on the high at 95F is 258 psi at idle. 325 psi is too high, especially at idle.
Too much R134a. 89 year should be 39 to 40 oz if you have a very good vacuum and purge the system with nitrogen or refrigerant.

If you keep driving around with those high pressures you are going to stress the compressor over time. And, you will end up with a 100 page thread (Discseven )

[Steve Marshall]

Originally Posted by Quicksilver

Adding an electric fan to pull air into the engine compartment would be pointless because it can't move anywhere as much air as the engine fan.

There are quite a few german cars that run electric/engine driven fan combinations and they have superior AC to a stock Carrera. The results we are getting by adding electric cooling fans are well worth the effort.

Originally Posted by kuehl

Bogey on the high at 95F is 258 psi at idle. 325 psi is too high, especially at idle.
Too much R134a. 89 year should be 39 to 40 oz if you have a very good vacuum and purge the system with nitrogen or refrigerant.

Thanks for the input. I'm going to revisit the high pressure on next hot day and see if I can get it down.

[kuehl]

Originally Posted by Steve Marshall

There are quite a few german cars that run electric/engine driven fan combinations and they have superior AC to a stock Carrera. The results we are getting by adding electric cooling fans are well worth the effort.

Yup, there are quite a few cars with radiators, condensers and engines in the front of the car with electric fans.

However, the 911's engine cooling fan starts to produce a higher cfm above 1500-2000 rpms. And that cfm exceeds what any electric fan(s) you can adapt to the 911 or 930 engine deck lid condenser(s); to the point were the small electric fans on the deck lid impede the air flow and heat transfer. They might work a bit to help at idle rpm however they 'get in the way'. If adding electric cooling fans was the magic bullet that is what everyone would have done 30 years ago.

[Steve Marshall]

Originally Posted by kuehl

If adding electric cooling fans was the magic bullet that is what everyone would have done 30 years ago.

I don't remember what all the options were 30 years ago when I was daily driving a 78 Targa in Dallas. I do remember paying a pretty good bill for an AC upgrade that at a minimum included I believe a Sanden compressor and maybe an evaporator? What I do specifically remember is that it worked okay if the temp was around 90 or less and I was at 65 mph with no traffic. Once you slowed down or got caught in traffic, which was the default scenario where I lived, the system would fall behind and never really catch back up. In spite of the high "at speed" volume of air moved by he early 60's 911 cooling design it was barely capable of keeping the engine cool, much less the AC functioning, in traffic or at idle in Texas heat. I'm surprised they weren't using electric fans back then. Maybe they just weren't available in a size that would squeeze into the engine compartment?

I've heard about the theory that at speed cooling fans could impede the air flow but I've never experienced it. I guess this would manifest in higher engine temps? I'm running cooler with the electric fans, including one on the oil cooler. It's Africa hot in central Texas. On a slow summer we get 30 days over 100° and at least 65 days where the high is never below 90°. I never get to 2/3's hot even sitting. At speed, when theoretically the cooling fans would impede air flow, I'm seeing half hot or below on the temp gauge.

Investing in more than just fans will provide better overall performance and reliability which is why I've done just that. But for adding a couple of fans we had laying around I'd say the results were pretty good and certainly worth the effort.