I need some help here folks... and let me say in advance that I appreciate anyone who takes the time. I'm not exactly well versed in the nuances of engines in general, though I have a natural talent for troubleshooting and can understand / follow directions well.. just more of a computer guy than a car guy.

I have a 99 SL2 that I use as a commuting vehicle. It has about 160k on it. This car has always ran flawlessly and everything has always worked properly. As of yesterday, the service light (one with the wrench icon) came on. The service engine soon light has been on for some time, and I know it's irresponsible, but I've ignored that one, because everything has been functionally fine. With the advent of the wrench light, the car now gets hot when idling for too long. Previously, when the temperature gague reached just above the halfway mark, the radiator fan would kick on and cool it back down to between 1/4 and 1/2. Now, it just keeps rising. At about 3/4 I get concerned, and turn the heater on, which pulls heat off and takes me back down to 1/2.

I turned the A/C on, and watched the radiator fan for several minutes. The fan didn't move. I assumed this was the cause of the overheating, and that I'd first start looking at the fuse and ECTS.. however... I've also noticed that the A/C no longer blows anything but alternating warm and hot air (worked fine before yesterday). I also notice..(and this is going to illustrate my lack of knowledge) that the part of the A/C compressor that the belt goes around has a front face to it labeled "uni damp". The piece that says unidamp spins with the belt... then stops.. then spins with the belt again...then stops again.. the engine changing tones as it does. Is that normal? Is there a "likely scenario" I'm looking at here, or should I just bite the bullet and pay my mechanics diagnostic fee?

 

OK -- Couple of things going on here ...

1) Repeated cycling of the A/C compressor. Usually indicates a system low in refrigerant. The change in engine tone is due to the additional load/strain when the compressor engages. No worries there, however low refrigerant can lead to insufficient cold air inside the car.

2) Radiator cooling fan does not run. Could be simply a blown fuse, or a defective fan relay, a burned out fan, bad wiring or even a defective ECTS. With the A/C controls set to maximum cold, and recirculate, the cooling fan should run when the A/C is turned on. I'd check for a bad fuse, then a bad relay, then a bad fan, and finally for bad wiring. I don't believe that the ECTS is bad, although it is a remote possibility.

Let me know what you find ......

 

Yessir. And thank you. Can I charge the AC myself, with one of those dinky little kits at Wal-Mart, or should a shop do that? Also, just out of curiosity, that compressor should always be spinning right?

I'll check the fuse. If that's not it I'll have to find out where the relay is and go from there.

I suppose I freaked a little bit because this all started happening on the same day, I assumed there must be some overall systemic problem, rather than looking at it as individual elements.

Thanks Again!
Nick

 

Well, if you have recharged an A/C system before, then you should have no problems. If you are a 'newbie' at this, it might be better to have a shop do the work. The compressor will be spinning only when the A/C is turned on, otherwise, just the outside ring on the pully will turn ...

 

Ok.. one mystery solved. Went out on a break with a pair of pliars and pulled that fuse.. blown like Bill Clinton. I doubt that'll fix the hot air out of the AC, but I'm assuming once I replace that fuse the radiator fan will start working again!

 

Ugh.. the plot thickens... I replaced the fuse, and the fan still didn't run. I checked the new fuse, and it was already blown. So I tried another one. The fuse remained in tact, until I turned on the AC.. then it blew. Then I replaced the relay, and put in a new fuse. Same thing.. as soon as the AC goes on, the fan fuse blows. I'm assuming this means that the motor for the radiator fan is bad....

Another interesting thing to note. Just out of curiosity, I turned on the AC while I was on the interstate, and it blew ice cold air like it used to... so somehow the proper functioning of that AC is related to air cooling the radiator, or what?

 

Exactly ... highway speeds force air through the condensor coils of the A/C, cooling the high pressure gas from the compressor the fan 'helps' out when running in traffic. Sounds like a bad fan motor ....

 

Thank you very much for your help and explanations OA.