What is the "front" radiator on a 1982 240d?

[herring]

I am away from home right now so don't have access to my service manual. I've just completed an hour of driving and while checking the oil level I noticed that the area right behind the front grille wasn't as hot as I expected. When I checked I found that the car seems to really have two radiators, one immediately in front of the other. The one in front is not hot at all, room temperature. The one behind it is very hot, as you'd expect a radiator to be. So is the small, narrow "third" radiator to the right (as I'm facing the engine compartment), which I think is a cooler for the automatic transmission.

I've attached a picture...the whole part in front (with the fan on it) is evenly cool to the touch, while the part that's mostly hidden behind it is very hot.

What is the difference between these two? I assume it's a bad sign that the front one isn't hot? What should I check?

[Demothen]

Front one is your AC condenser. It should only get hot when the AC is running.

The largest section (in the back) is the radiator for the engine coolant.

The slim radiator on the driver's side is for engine oil.

The bottom of the large radiator will be for automatic transmission fluid.

So if that front radiator (condenser) is not hot, there's no concern unless you are attempting to operate the AC.

FYI - the electric fan is an auxiliary fan, it should engage part-time when the AC is running, it is controlled by a thermal switch in the receiver drier (a metal canister located behind the passenger side headlight)

[herring]

Thank you for explaining that! I'm less concerned now. I say "less" because I did in fact have the a/c on some. If the a/c is working (blows cold air) can I assume that everything's ok? Is there a link to a checklist for proper a/c operation?

[Demothen]

Hmm, if the AC is working and producing cold air, it has to be producing waste heat - and that's where it should go. Unfortunately, I can't tell you how hot it should be, since my AC never has really worked - and I'm in the process of rebuilding it.

If you were checking the oil, presumably the car had been turned off for a minute or two? Not sure how quickly the condenser will cool down after it's been up to temperature, but it doesn't have a ton of thermal mass (~3lb of refrigerant and oil in that circuit, vs ~3 gallons of water/coolant in the big radiator) so it should cool down pretty quickly compared to the actual coolant radiator.

[leathermang]

Between the compressor and half way through the condensor the theory is that should be hot vapor.... from half way down the condensor to the Txvalve should be hot liquid... after entering the evaporator through the Txvalve the evaporator should be cold and then exiting the evaporator and back to the compressor vapor should be approximately ambient air temperature....
So for the condensor to be cold at any point where the AC is running... is problematic.
The condensor is supposed to cool the hot vapor to a point where it can be turned into hot liquid... it is the phase change from liquid to vapor inside the evaporator with air blowing across the fins which should provide the cold air needed by the occupants of the car...it is where the ' excess' heat taken from the air inside the passenger compartment is released into the outside air stream...