Yesterday I was helping a friend with his A/C on a 2001 BMW 540i. The setup was very nice. It had a dedicated, fully shrouded fan front-mounted on the condenser. As I charged the car and pressure rose, the PWM boosted the fan up. The fan basically idled in silence under 200psi, ramped up gradually to 250psi. Over 250 the speed rose and fell very aggressively. It was awesome to hear the fan spool up, watch the pressures fall, then watch the cycle repeat. Once the cabin temp was stable, the fan speed would stabilize as well. Turn the interior fan speed up (increased load) and the condenser fan would ramp. Turn the interior fan down (reduced load) and the condenser fan would ramp down.


Now I don't know if there is a pressure transducer and the PWM is responding to that signal or if there is merely a temperature sensor and the PWM was responding to that signal. It really doesn't matter; either one would work, since pressure and temperature are directly proportional.


Very, very cool in every sense of the word!

 

if only I could my ac finally working. Still have to play with the pressure.

 

yeah sophisticated engine management is something you miss on old cars like Rx-7's

 

i recently got my A/c working in my FC.. i never really took the time before now to see how it works. basically the bigger the pressure drop between the low and high sides, the better the cooling, and the more air through the condensor increases the pressure difference.

but yeah that would be a cool aftermarket device.. a closed loop a/c fan controller using an a/c pressure sensor for feedback, it could easily attach to the low side charge connector. hmmm

 

The auxilary fan on the BMW is controlled directly by the DME(engine control unit). Which takes reading from the coolant temp sensor, and the A/C controller.
I'm not too familiar with Haltech ECUs, but I bet it could control both an engine radiator fan and a condenser fan.

 

LOL, welcome to one of the many reasons why the better RX-7s have a standalone EMS as opposed to the stock POS EMS jury-rigged with a POS piggyback fuel controller. You can also buy a fancy fan controller box such as the Spal FAN-PWM:
http://www.spal-usa.com/fans/automat...es/fanpwm.html

 

it doesn't matter how good your fan is or your ECU is, the piece of **** blower motors are the weak link in the A/C system

 

I was just about to have hope of using my A/C in my car again. I wanted to install a nice fan for the condenser in hopes of cool air....but now you've crushed my dreams once more...

My FC is an oven in California right now....and I'm the piece of meat going medium rare as I drive.

 

You may say they the factory EMS is a POS, but just an FYI, the S5 TII we purchased new is now 21+ years old, 199,000 miles and has never had an A/C problem.

 

I've never had a problem with a/c until it got in my way for making power, which it does. yay for the midwest, burr it's chilly.

 

The fan isn't really necessary for a/c, as long as you have a working and ducted clutch fan, you should have decent cooling. The fan helps though when you're stuck in traffic. Some FC's didn't have the fan from the factory.

 

My clutch fan died on me awhile ago and I went with a 16" e-fan from flex-a-lite. It moves a whole lot of air...2500 cfm. But when I turn on my A/C the stock S5 TII Alternator can't keep up and the fan loses some power...enough to have the water boil. I haven't used my A/C ever since that overheating incident. I'm waiting for my alternator from Japan2LA then I wanted to give the AC another try with an e-fan. That Spal fan controller is pretty cool but expensive...I might just get a thermostat controlled e-fan like the radiator fan I'm currently using.

I so agree with you on the ducts! My original undertray was MIA before I bought the car, I've been wanting to go get some sheet metal and fab up ducts that lead to the oil cooler and radiator seperately. I've seen a few members here do ducts like that to help their V-Mount.