308 gts radiator / AC fans

A little weird but here it goes. (long explanation for short question)
Since I got the idle rpm low enough to advance the timing to 7degrees BTC at idle and 34 degrees at 5K (pertronix that has no retard micro switch which means I have 10 degrees more ignition lead below 2000 rpm or whenever the microswitch cuts in) it runs cooler around town especially at idle (which it is a good portion of the time) in fact it runs cool enough that when the AC is on only the AC radiator fan is on most of the time. I can let it idle for an hour in 90 degree weather with the ac on and the second fan never comes on and the temp never gets to 190 and yes with the AC off both fans come on at about 195 degrees. Sounds great except I noticed a 5 degree increase in AC temp (from 35 degrees to 40 degrees) when only the AC fan is on. (not as much air flow over the condenser?) so I am toying with the idea of having both fans turn on when the AC is on. I think I saw a thread about this but can't find it. Does anyone have a mod or can reference a thread which would turn on both fans when the AC is on without overloading the AC fan circuit by just jumping the cooling to the AC Fan. I guess this is "Having your cake and eating it too".

Thanks
Barry

 

Before you do this ..does the ac get cold if you rev the engine ..i saying that because maybe the compressor at low RPMs isnt effective as when driving (reving)

If not the case disregard

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Its cold all the time just colder if both fans are running while driving around town at low speed or idling. It runs at 35 degrees at freeway speeds no matter what the outside temp is so it seems to me to be a air flow over the condenser issue. Its actually two cold when at high at freeway speeds so I turn the temp up. I live in So Cal so we have plenty of hot days. In fact it was 92 in my yard today.

Barry

 

FWIW when I re-cored my radiator I went with 2 less FPI (fins per inch) it increased airflow across the system. No problem with radiator temps and lower speed AC temps. Also rebuilt the OEM fan motor brushes.

 

The condensor doesn't work in exactly the same manner that a radiator does. While the both cool the contents, the contents are in completely different states.

The coolant in the radiator doesn't boil; it remains a liquid. The fan, of course, removes the heat from the liquid. More fans remove more heat from it.

Inside the condensor, the refrigerant is in a boiled/gaseous state, and the cooling effect of the fan turns it back into a liquid and then passes (in liquid form) back to the expansion valve. It is not the condensor fan which removes the heat from inside the car, it's the evaporator fan.

Thus, I don't see that adding another active fan to the condensor would result in colder AC.

 

Can't agree -- the colder the liquid is entering the expansion valve, the colder the evaporator will be, so rejecting more heat from the liquid exiting the condensor is a plus.

 

100 percent

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I see your point, and I'm by no means an expert on thermal mechanics. Obviously, yes - a cooler liquid has more heat-absorbing potential than a warmer one, before boiling. But how many BTU/cc would we expect a second fan to increase absorption capacity by? Enough to make a 5F difference?

(Sorry if it sounds like I'm being snarky at you, Steve - I'm not. Just sort of trying to think it through...)

It just seems to me that with 90F ambient, the difference of 35F to 40F at the vent is nearly in a margin-of-error performance range.

As always, interested in learning more about things about which I know less... so, all corrections to my pondering are welcome.

 

Low air flow reduces sub cooling which in turn reduces superheating .. same as if refrigerant is low or over charged in more modern systems

Superheating is basically how much heat will be removed in evaporator

Lower temp and pressure output from condenser will allow for more gas evaporation in evaporator . Thus more superheating and colder cabin

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Back to your question bl10, to easily prove your theory you could just jumper the two wires on the thermoswitch in the bottom of the radiator. That would make both fans run all the time. If after trying that out you think this is a worthwhile mod we could probably find a place to put a wire or diode to tie the two circuits together.

 

Thanks guys
Brian I may try jumping the fans so both are on all the time, however, I'm pretty sure both fans on will reduce AC temp while sitting in traffic to a point otherwise why use the fan at all. I've jumped them before when I was having fuse connectivity problems (I soldered the fuse box sandwich connections and all is good now). I could jumper the fans and let it run (idle) for a while and check. I still use the original fans albeit cleaned up. I tried a couple of cheap (mistake) modern fans (ebay) and it actually ran hotter around town so back to stock. The radiator is all original and as far as I know never been out of the car.

Anyway back to my original question does anyone have the link to the thread that describes modifying the AC fan circuit so both fans come on when the AC is on. The only down side I see to this mod is that both fans would run at highway speeds where probably even one is not necessary. Another question just popped up. Does anyone know if the AC fan continues running when the AC cycles the compressor when the cabin temp gets to cold?. I assume it does but not sure.

 

Please be more specific about your exact model/year/version.

 

Hi Steve
Sorry its a 1978 GTS US.

 

I agree with Steve. Back when charging 308 A/C was a near daily occurrence they were marginal enough and we were in a hot environment, static in the shop getting outlet temps down below 40 we considered it a victory. A few degrees in a less than optimal test condition translated to a noticeable improvement out on the road with a lot of airflow. Sitting in traffic with a preheated stagnant airflow is pretty sub optimal.

In any event the mod is easy and he'll know soon enough if it works.

As far as the engine coolant temps the stock but properly working cooling system in carbed 308s worked very well with some reserve in traffic on hot days. It wasn't until the 4 valves when our reserves were gone and watching the gauge on a hot day was not a bad idea.

 

Rifledriver
I agree 5 degrees is not much. Just playing around now that I FINALLY!!! got the thing to idle like it should with no R2 points and timing set to factory total advance. Also we live is So Cal and take trips to Death Valley, Los Wages and the Mojave desert where outside temps can be 115 degrees and every little bit helps.

 

I know. We used to live in Diablo Valley and 100+ in summer was not unusual. Here in Austin it is actually cooler at peak daytime.

5 degrees sitting in a greenhouse is important.


Please tell me you are using R12.

 

Are you saying that you're having a memory of someone actually posting such a thread for your car? On your car, I think the only way to do this is add a relay (not just some wiring changes), but I'll think about it a bit more.

No, the AC compressor clutch "on" signal is what's used to actuate the relay that runs the RH fan only. (Assuming the water thermoswitch in the radiator is not closed and running both fans) When the AC compressor clutch is "on", the RH fan is "on", and, likewise, whenever the AC compressor clutch is "off", the RH fan is "off".

 

I've changed my mind . I think it is possible to just rewire the "relay D - Relay for radiator right fan with operating air conditioner" (Relay 99 on the OM schematic) to change its function from supplying big +12V power to run the RH fan directly when the AC is "on" to being something that does the same thing as the water thermoswitch in the radiator and puts a ground signal on relays B and C to close them to run both fans whenever the AC is "on". (Give me a few days to create a diagram of the wiring changes.)

However, I'm still a little confused as to how often, or why, you need this, and am surprised that stationary on a hot day with the AC "on", and only one fan running, the radiator water thermoswitch never closes to run both fans as you report?

 

Steve
Thanks so much for you input and wealth of knowledge about these 308s and thanks for the wiring explanation.

Here's my take on what's going on. (Long explanation but a lot of moving parts)

So I took it on a fairly long drive yesterday both on the freeway and surface streets in traffic. I ran it very hard through the gears getting on the freeway (runs great now, really pulls hard considering the relativity low horse power. The gearing is perfect in my opinion) plus running about 75 mph for several miles. AC temp at lower vents right at 35 degrees with interior fan all the way up (AC temp drops a little on low fan setting). It was bright and about 90 degrees outside. Engine temp about 185 - 190 degrees. Pulled over with it idling and only AC fan was on, turned AC off and both fans remained off until 195 degrees then both turned on. Off the freeway in traffic about 20 min with AC on. AC temp 40 degrees (5 degree increase over freeway), engine temp still at 185 - 190 checked the fans and only right (AC) fan on. Turned AC off while idling and temp rose to 195 and both fans came on for a while, temp went down a little and fans cycled off. And repeat. Turned AC on (still idling) while both fans were on. After a bit the left fan turned off and stayed off. Temp at 185 - 190. It seems the AC (right) fan is enough to keep it blow the thermo switch trigger point.

In thinking about it I believe the reason for this is the additional 10 degrees initial ignition timing I'm running due to lack of R2 points (Pertronix). On mine when I was running the R2 points and idle was a little under 1000 rpm if I disconnected the R2 points which advanced the timing 10 degrees the idle rpm increased to about 1500 rpm indicating to me the engine liked the additional timing. In order to get the idle back to 975 rpm or so I had to mess endlessly with the carb sync and virtually have everything closed with the idle speed screws just touching the carb levers. I even closed the carb barrel balance screws. So now its showing between 3.5 and 4 kg/h across the board and is pulling 18 inches of vacuum. The idle mixture screws are between 4 and 4 1/2 turns out and I'm running size 60 idle jets.

Something else that may contribute is that I have the engine cam separation angle set to 111 degrees, up from 109 degrees stock with 1 degree overall cam advance, stock is 0 degrees. Increasing the cam separation angle reduces cam overlap which smooth's out the idle and increases vacuum. The came advance also helps torque at idle. The setup I'm running now has completely eliminated the "popping" back through the carbs when cold and has the fast idle cam working great. I start it ice cold and within a few seconds its idling at about 950 rpm and gradually increases to 975 as it gets warm. Its running better than it ever has.

For anyone interested:
78 308 US
New radiator (I think) in 1983 or so due to fender bender. Maybe the radiator is different than the original but it appears to be OEM. I'll check the part number if I can find it.
Stock original fans.
Original thermostat.
Replacement water pump.
Stock AC including original dryer.
R134
R134 compatible compressor oil.
50/50 antifreeze always which I think contributed to lack of corrosion when I had to pull the rear head to replace bent valves.
Overflow tank (like new cars) which keeps the expansion tank full at all times reducing rust and corrosion.
Pertronix ignition in rear distributor.
Pertorinx coils.
Derek White's cam pully setup with round tooth belts. (great addition)
Cams degreed to 111 degrees separation angle and 1 degree overall advance.
Compression 145 to 155 all around. Leak down 8 to 10 percent. (Tested when cold)
Timing at 34 degrees at 5k rpm.
Smog pump disconnected.
Smog manifolds and air injectors installed.
Empty Cats (I reinstall good cats and the smog pump for CA smog check which its always passed with flying colors)
Vacuum lines from carbs per Steve's drawing.
Jets
Idle 60
Main 130
Emulsion tube F36 (stock)
Air Corrector 200 (stock)
Starter 60F5 (stock)
Accelerator Pump Squitter 2 sizes richer
68K miles
.

 

The modification is usually in the reverse, on the early cars.

The radiator temp brings on one, the A/c circuit brings on Fan 2
Just wire them both to come on with coolant temp, and the A/c status has no bearing.

 

Big Tex
I think your missing the point. When the AC is on the AC fan seems to be providing enough air flow over the radiator to keep the thermo switch from reaching sufficient temp to turn on there by limiting air flow over the condenser to one fan. I want both fans on whenever the AC is on not just when the temp is hot enough to trigger the thermo switch.

Barru

 

I suspect your thermo switch is cooked from previous overheating, it has failed..

NO WAY ever, the two cheesy fans in the front of the ac condensor would drop the HOT water from the engine at 220 degrees F to below the threshold of the 160 degree thermo switch. There's just no way, and here the ambient air they are handling might approach 100 degrees F

The heat from the engine is non stop and resupplied by the second......at 220 to 240 degrees F

 

This decribes the stock Factory wiring, the air conditioning brings on the second fan, always....despite thermo switcch closure.

 

Big Tex
I'm going by the factory temp gauge. It never gets to 200. Temp fans come on at about 195 at which point temp drops to 185. (around town). With the AC on (left fan) the temp generally stays in the 190 range with only the AC fan on. On a really hot day the thermo switch will turn on the right fan. It runs about 170 on the open road no matter what the outside temp is. I know it sounds goofy considering all the heating problems everyone has but I just don't see it. I tried some cheap modern 11 inch fans and it ran hotter so back to the stock ones. I've had the car since 1980 (its a 78) and have never even approached overheating. As far as I know the cooling system is original except a couple of hoses and the water pump. I did have a small leak on the top seam of the rad which I soldered this past weekend with rad in car. AC temp on highway is 35 degrees at console vent and around 40 degrees around town. It takes a while to cool the cabin down if its been sitting in the sun for any length of time but is comfortable after about 10 minutes and cold enough to where my wife, Sonia, directs the air away from her. On the highway I turn the temp down to about 1/2 otherwise its too cold. I think everything is working fine just trying to get the rt fan to come on when the ac is on. I'm going to change the drier this weekend, maybe that will help the around town temp. The one that's installed now is the original from the r12 days. Image Unavailable, Please Login Image Unavailable, Please Login
View attachment 3289348

 

Barry -- These figures describe the stock radiator fan system and the two wiring modifications to run both radiator fans when the AC is "on" (but the coolant thermoswitch in the radiator is not closed). All of the 2-valve 308s are exactly the same in this regard, and even the 308QV have the same system architecture, but they changed some of the wire insulation colors on the QVs (and they run so hot they'd never ever need this ).

A word of warning -- I prepared these diagrams using the information shown on the schematic in the 150/78 OM for 1978-79 US 308GTB/S. However, these Bosch ...113 relays work just fine if the wires on terminals 30 and 87 are reversed or if the wires on terminals 85 and 86 are reversed. Not sure that Ferrari was always super-careful to assure that the schematic matched how the car was built. If you find that a wire insulation color and relay terminal number on these diagrams does not match your car, best to use the wire insulation color for what to cut and how to connect (and please let me know if you do find any of these wires are swapped).

Here's the stock 308 radiator fan system:

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And the modified system (with modification instructions) to run both radiator fans with AC "on":

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Attached are pdfs of both (so you can enlarge them for better viewing).