740 - compressor fan just behind grille

petershen1984 · Post by **petershen1984** » 25 May 2004, 20:06

Hi, my 740 has a belt-driven cooling fan for the engine, but also has an electric fan in front of the radiator, visible through the front grille. I believe this electric fan is supposed to operate in conjunction with the A/C compressor, but that hasn't been the case lately. The electric fan doesn't spin, but the A/C otherwise functions normally - I'm getting cold air, the dryer is chilled, and the compressor clutch operates normally. I'm not getting any signs of engine overheating, either.

Should I be concerned with this fan? Perhaps this is just one of several electrical failures my car has been suffering from..

LaRy · Post by **LaRy** » 26 May 2004, 12:29

This fan is probably started by some sensor checking the cooling medium r134a temperature somewhere close to the condensor. (In some systems the increase pressure is starting the electrical fan). When the temperature of the r134a increase the pressure also increase and that is not good. It can actually increase to a forbidden level. Normally you have an over presure security switch switching off the compressor if the pressure is really to high, but it is definitely not good to reach that level. My oppinion is that this fan must be working, espcecially if you have changed from r12 to the newer r134 and live in a hot country like Taiwan. The reason for this is that r134a is using a higher pressure in the system compared to the older R12.

arete · Post by **arete** » 26 May 2004, 13:01

That front electric fan is probably a sensor driven fan. If so, it would only kick in when the water temp reaches a certain temp. I don't think it has anything to do with the a/c system, other than to make sure your car doesn't over heat. If you can, trace back the electric connections and see if you can find where the temp sensor is that activates it.
I installed an electric thermostatically controlled fan in my 81 240 as my main fan. It works very well. I can set the temp that activates the fan and it works automatically with a manual override.

petershen1984 · Post by **petershen1984** » 26 May 2004, 19:36

Yea, I thought this was abnormal because usually I can hear the fan right after I start up my car. My A/C isn't thermostatically controlled - it's operated with a slider switch that, when in the maximum position ( the largest "snow flake" icon), probably activates a timed relay for a few minutes at a time. As you probably know, LaRy, there's a handful of electric problems with my car - like that defrost ground problem that depleted my battery in March

My system was retrofitted to R134a by the young "FordVo" mechanics at OEM Volvo whom lacks experience with the older generations. Since the retrofit procedure last November I had to refill three times under warranty because of R134a leaks. (although, the initial job itself was expensive and probably pays for redoing it!), but having to revisit the mechanic this often is starting to get annoying.

I've had too much $$ invested into this car to give it up now.

petershen1984 · Post by **petershen1984** » 26 May 2004, 19:49

Thanks arete, my B200E drives its own cooling fan mechanically, so I don't have thermostat failure issues.

Volvord · Post by **Volvord** » 26 May 2004, 20:11

The electric "pusher" fan is thermoststically controled. When radiator coolant temperature reaches about 210 deg F the fan will come on. Because this temp is above the normal thermostat opening this electric fan is seldom needed, but on the turbo cars which have an intercooler, radiator, trany cooler, oil cooler, and A/C condensor all in the front of the car the extra air movement is sometimes needed.

Guest · Post by **Guest** » 27 May 2004, 23:41

Hey folks, the problem was traced to a broken Taiwanese relay and loose wires. My fan was modified with this timed relay switch to activate the fan and help cool the air conditioning refrigerant. The new relay from Germany feeds more power and makes the fan spin faster than before. Sigh..