96 SL320 getting hot at idle - PeachParts Mercedes-Benz Forum

bwheitman · #1 01-04-2005, 10:41 AM

It is pretty warm here in Texas, reasonably warm for the season, about 60-70 degrees F. My SL is running hotter than normal, when in traffic the temp gauge is going up to 100 C. It just started doing this, it has otherwise always floated between 80 and 90. Once I start moving it cools down really quickly. The car has 120k on it, the entire cooling system was serviced, water pump, stat, belt, flush, and radiator cleaning. It operated perfectly for almost a year. I noticed last night after I activated my Sirius Satelite (was sitting in the car with the engine running) that the AC was running not very cold. I moved the temp all the way down, still just a little colder than norm. With the AC going full blast the AC compressor is on, the Aux fans in the front are not on. Is there a separate pressure switch in the AC system for the fans? If those fans are not running at idle it will burn up my compressor. What should I check first? Thanks for any ideas!
Best Regards,
Brian

G-Benz · #2 01-04-2005, 11:03 AM

The aux fans are activated via the engine temp sensor and the A/C compressor switch. Your fans operating (or not) shouldn't affect your compressor operation (MB placed another circuit to shut down the compressor under certain circumstances for protection), but with the A/C on, the condenser radiator sits in front of the engine radiator and your engine is drawing heat from it, hence the higher temps.

Check fuses first (of course). Next, pull the plug off the temp sensor (near the front of the engine next to the valve cover just beside the water pump). The aux fans should roar on full if you do this. If this isn't happening, the aux fan circuit is at fault.

I can tell you much about diagnosing the circuit on the A/C side though...sorry.

bwheitman · #3 01-04-2005, 07:59 PM

I pulled the connector loose from the top of the thermostat housing above the water pump, I think that is what you said to do. When I disconnected the single lead wire, the temp gauge on the dash went to "0" When I pulled the 4 prong plug, nothing happened. I guess this tells me there is something wrong with the relay. I also checked the pressure in my AC system, it is corect, but just hair low. The compressor kicks on and stays on, but the fans do not engage. I understand the relay is behind the fuse panel, which relay is it on the 129 chasis car? Any help is appreciated! Thanks,
Brian

bwheitman · #4 01-04-2005, 11:40 PM

Well I got on Startek, I found my relay for the fans, it tested and is fine. I also found the secondary switch from the AC system, there are two, one has a green connector. If you jump those two wires it kicks on, so I know the fans work. There was a statement in diagnostic that the outside temps had to be over 86 degrees? is that correct? so maybe the fans are not supposed to come on? oh well, more tinkering tomorrow, who know what I will find.
Brian