Radiator fan dilemma

Hi I know this is debated again and again, but this is a new angle to an old story (at least that is what I hope). My AC is out of order for a short time, and hence the fans dont run continuously. Thus the temps rise to something like 92-93 degC before fans come on, I want it to stay at 81-82 degC as it does with AC on. so I thought it was the hispeed fans that turn and not low speed. Fiddling with the relays, it is evident that AC turns on stage1 low speed, and probably the hispeeds turn on at that upper temp of just over 90. So the fans work fine at both speeds, jumped from the relays. 1) So logic would have it that the low speeds should turn on without the AC, but why dont they? 2) or is it at that 91-92 the low speeds that are in fact on? If so how can I make them turn on at a lower temp? Jumping the relays mean its always on, even with ignition off, so that's not an option. Any help appreciated Mike

Quotes source post: 9650273

Why mess with the car's electrics? The engine will be fine with the fans only coming on when the coolant temp rises to 212F. The fans shut off when the coolant drops to 205F. (Those of us that live in warmer climes see this happen over and over again with no harm. My experience even in the hottest temps (116F) the coolant temp never climbs above 226F. Any modern water cooled Porsche with a properly functioning cooling system can well tolerate this.) In fact if the coolant got hotter once in a while this might a good thing in your car's case because I suspect with the lower coolant temps the oil doesn't get hot enough to boil the water out and the oil probably sees a pretty rapid build up of water. This lowers the ability of the oil to do its job. My advice would be to leave the fan circuitry alone and get that A/C compressor problem fixed and the A/C system working. If you don't before you know it you'll let it go too long and the rest of the A/C system will degrade due to lack of use and you could then be facing a bigger repair bill. When a car's first problem is ignored, its repair postponed, or worked around or bailing wire and duct taped patched, the car begins its downward spiral to a beater. Including a 996 Porsche. Sincerely, Macster.

It goes in for AC repair in a few weeks - so not a long-term situation at all. So those 90-95 degC temps are not a problem at all? OK...but why is the car set up so that when AC on, the temps stay at a lower temp overall, i.e. the thermostat opens fully at that lower temp and keeps it there. I've never seen this behaviour in any other car, which I thought was strange. I appreciate your thoughts and just reasoning through the logic is good to do.

Quotes source post: 9650551

Briefly, in case you missed it, I drove my Boxster thru mid-July AZ 116F temps and the coolant temp stayed at 226F, the radiator fans ran high speed, intake air temp was 135F and the engine compartment ran until nearly Xmas. In spite of the above the car the engine appeared unfazed. Just in case, though, when I returned home I spoke with my SM and he forwarded the above to the factory. The word back was no warning lights, no problem. That was at least 100K miles and probably more than that, a lot more, ago and the car and its engine is fine. I'll stress this again: "high" temps with properly operating cooling system do not phase these cars. A qualifier is the engine oil must be reasonably fresh and of the proper type of oil. A 'watery' oil or the wrong type of oil may not be able to protect the engine even if the cooling system does keep the coolant (and oil temp) to below acceptable levels. That the coolant temp stays lower when the A/C is on is a side effect of the fans running all the time. They need to run all the time because the A/C system presents an additional and substantial heat load that has to be dealt with, shed, and the A/C system can't well tolerate the 'wide' swings (relatively speaking) the engine and its cooling system can and do tolerate, day after day. Actually this works to reduce wear and tear on the A/C system for it can be adjusted if autoclimate control to produce more or less cooling by varying the compressor's displacement but the electric fan motors are cheaper to replace --- not that they go bad all that often -- and affect the parasitic load to the engine less by running all the time than a compressor having its displacement constantly adjusted in reaction to a the amount of cooling available from passing air. This A/C heat load is shed via the condensors one of which is in front of each radiator. The A/C heat load then reduces the cooling system effiiciency somewhat in that the air temp of the air passing through the radiators is raised a considerable amount over ambient. Believe it or not, in spite of the appearance that air just howls through the radiator duct openings this is not the case. Both the condensor and radiator do not readly pass air and as speed goes up they act more like barriers to air flowing through them. The radiator fans are there to help move air through when the heat load is more than the air flow provided for by the aerodynamics and the car's speed can provide, and of course to move air through when the car is stopped. Under some conditions -- I have seen this at least once with my Turbo -- with the A/C on and on a mild day when I was driving through some mountains and the outside temp swings sometimes 20 or more degrees in just a few miles -- the coolant temp can drop a noticeable amount. I've seen it drop based on the coolant gage needle's position by several needle widths below where the needle usually resides. There also might be a little hysteresis in the t-stat. Once it has been exposed to hot enough coolant to open beyond a certain point it may take some additional time being exposed to cooler coolant to cause it to partially close again. Also, if you are relying upon the temp gage and its needle do not put much weight on the needle on the 180 mark. My experience is these gages are not that precise and the only real way to know the coolant temp is to if the car's on-board computer doesn't offer this data to read the coolant temp in real time using an OBD2 code reader/data viewer/logger. Get the A/C problem taken care of. Then relax. Your car's fine if you can tell me the cooling system does not lose coolant and there are no real signs of cooling problems. Sincerely, Macster.

Here is a solution, I did this to my car and my '99 runs cool in the 105+ temps we have here in Phoenix for 4 months. It works! The relay box is to the right and above the fuse box. It's very hard to read the relay numbers. You want relay number 20 & 22. They are on the bottom row (the row closet tothe floor) and last on right (22) and two over (20). If you have fat fingers use a large needlenose to gently pull it out. There are 4 prongs, #85 is the one you use, it's marker on the underside of the relay. Imagine a n,s,e,w when looking at the empty relay socket. # 85 is the e prong. Put some 16/18 wire in the little slit and jam the relay back in, press firmly. Turn your key on and touch the other bare end to some metal, you should hear your fan come on. I routed the wire over some air duct an into the spot for your manuals under your steering wheel. For the ground wire, I unscrewed the screw by the gas pedal, sanded under the head a little to make sure there is bare metal to make a good ground. I stripped the wire 1/2 inch and wound it around the screw and tightened it up. I routed this wire over the air duct also and into the manual spot. I used those little female 1/4" solderless connectors on the wire ends. The single ground wire from the gas pedal slipped onto one of the male ends on the toggle switch. The two wires from the relay box slipped onto the male 2-1 male and this then this slipped onto the other male toggle. I taped the toggle just barely sticking out of the manual holder. Turn your key on, flick the toggle switch and you'll hear both fans turn on. The engine fan is the same but much easier because of the location. The relay box is under the carpet on the drivers side. Put your seatbacks down and pull out the thick foam piece. Unscrew the three nuts pull flip over the silver relay holder. The relay # is 8, it's easy to find since you can read the relay numbers on the relay holder. You use pin # 85 again. Slip the bare wire in and jam the relay back in. I used the front nut where you tighten the relay holder as my grounding location. I used 1' of wire for each wire, used the same connectors and slipped them on the two prong toggle switch. I have my seatbacks down so I have the toggle switch just sitting out of the seam from the thick piece of foam. I left extra wire under the foam for when I need to pull the toggle switch out further. You could run the wire from the relay all the way up to the same spot as your other toggle switch, use the gas pedal screw again for the ground as you did for the radiator toggle and have both toggle switches in the same location. Both mods took about 1.5 hours combined. I bet I could do both in 30 minutes now.

Quotes source post: 9650737

oil is four months old, 1000 miles on it 5-50 mobil1, still beige in colour. Coolant is at the right marks. no losses anywhere and nowadays oil dry too except usual sweat marks here and there. Everything is good in that sense. thanks for all the explanations. White99: I thought of a manual trigger switch, not a bad idea but as Macster said, probably overkill. Now, all I need to know is why my AC compressor makes a whiny noise...

The whiny noise means it is low on freon.