AC Condenser Fan Control

To answer your question about the condenser fan, it sucks air from the outside of the car. The trunk liner also needs to be installed to make it work correctly.

quote:

Originally posted by BD:
I have two questions for the forum readers on the AC condenser fan control –
1.Which direction should the fan blow air, suck it in from the back of the car or blow it out to the back? Searching the forum on this subject, what I found wasn't very clear to me. If there is a vacuum behind the car at speed I would think that the fan should blow out to the back of the car. However, my early 71 doesn't have much space between the fan and the trunk insert to suck air from and blow it out the back.
2.TSB #3 Article 17 calls for rewiring the AC condenser fan so that it runs whenever the heater/AC blower fan runs. Is this still recommended? Mine only runs when the AC compressor kicks in. TSB #9 Article 78 calls for replacing the de-icing switch with one that will also control the condenser fan but I don’t want to do that as it appears that I would have to remove the dash to get the switch temperature sensor out
Thanks for the help.

Like JFFR said the fan pulls air in from the back through the condenser coils and down on top of the ZF.

Here is what I think is a pretty neat solution for controlling the condenser fan http://www.panteraplace.com/Sub1/page312.html

Mike

Guys i am a little stunned that the air is sucked in by the fan rather than blown out. I run an after market fan and i specifically set it up so it blows out side the engine compartment. The only downfall i see is that its making the condensor use heated air from the engine compartment over the condensor, but id rather have that than sucking in exhaust fumes.

The car as designed was to suck air into the condenser from the outside. I am sure that there is some exhaust that gets pulled into the condenser, but perhaps only at idle. I have seen a case where the fan was wire backwards and the system did not work very well. On that particular car the trunk liner was installed, which by design should be installed for the air conditioning system to work correctly. It would be possible to move more air through the condenser by having the fan blowing the air out, however you are not only picking up heat from the engine block, there is also heat from the radiator that flows through that area from under the car.

I have run tests on engine inlet air engine temperatures on my Pantera. With the air coming into my throttle body from under the car, which is where it would come in from as the car was designed, I had an inlet air temperature of 120 degrees on a 80 degree ambient air temperature day. By pulling air into my sealed air box via the side scoops there was a 40 degree drop in temperature at 75 mph. I know these figures are correct because the fuel injection system measures inlet air temperature and I can see that reading in real time on my system dash monitor. There is also a stand alone outside air temperature gauge installed in the dash. Air at 120 degrees going through an air conditioning condenser does reduce its ability to exchange heat.

Just a note Hemihunter regarding sucking in exhaust fumes. I dont think it should be any big concern. Imaging your daily driver with the Condenser in the front right up behind the Car/exhaust in front off you at the Red Lights. It was really never any concern if we think about it. There is a lot colder Air going through the Condenser if it is sucked from the outside and in, making it more efficient.

To expand on JFFR's notes, most of the hot air from the radiator goes under the car and not all goes out the front wheelwells, so his air temps are believable. Some hot air does go up and out the rear 'window' over the rear decklid, maybe picking up more heat radiated from the header tubes.

We think there is a large vortex or swirl trailing behind the Pantera at almost any speed, from studying the contrails from Muroc dry lakes and Bonneville. This swirl snuggles up close to the back panel and is available to be sucked in by the AC fan. The AC exhaust hits the contoured decklid and is bent down closer to the road so it doesn't make a second pass.

But as speeds climb, the swirl lags further and further behind the car. This may be why the stock AC configuration drops off in efficiency as speeds climb. And somewhere around 100 mph, a partial vacuum begins behind the bumper and gets bigger with more speed. This could be why AC hoses sometimes overpressurize and blow at higher speeds if the AC is left on during the run: little air is available to be sucked in by the fan.

A lot of this is guesswork on some odd things going on back there- but I have a photo around of a GT-5 that ran the Silver State one year in the lower speed classes. The upswept exhaust tips MELTED both his tail light lenses! Hard to explain that without a swirl. There is also the Ferrari Boxer intake problem with the same type decklid.

I linked to an old video of a test dealing with the issue. If overpressure in the system is a concern I recommend as much "cool" Air as possible through the Condenser as Pressure and Temp are going hand in hand with Refrigerant. It is also a very good idea to install a pressure switch in series with the Magnetic Clutch on the Compressor to break the curcuit in case of over/under-pressure.


youtube video

The air flow over and under the Pantera is a surprise until you see one at speed in the rain! It is then you realize the rear sail is like a giant vacuum drawing huge amounts of air through the opening in the rear sail. It looks like a group of fire hoses shooting through the opening, the air moves up into the engine compartment and out the (vacuum creating) opening in the sail. This low pressure area in the engine compartment sucks air into the condenser opening in the rear of the car. Pushing air against the vacuum of the sail does not work, except at speeds under cruising speeds, i.e. stop and go traffic and then it is marginal as you are now pushing hot air across the condenser, I put a oil cooler in place of the condenser, it had to be partially block off, it worked to good!

The air flow sketch confirms what I see on the back of my car after driving it on a nice day on winding mountain roads where the speed varies between 30 and 70 mph. It seems that the back of the car is the first to collect and show dirt and exhaust by-products. This is an interesting discussion, thanks to all who contributed.