It switched off at about 112 degrees.

__________________
1982 240D - 292,000 miles and counting
Same family for 33 years
Newly rebuilt Monark injectors
Newly replaced clutch
New Bilstein shocks

Based on the troubleshooting, it sounds like I may be low on refrigerant. I don't know a lot (read: hardly anything at all) about air conditioning. How can I check to see if the old system needs a recharge? I last had it serviced in 2006, so I had a good run. . .

__________________
1982 240D - 292,000 miles and counting
Same family for 33 years
Newly rebuilt Monark injectors
Newly replaced clutch
New Bilstein shocks

Just because the Aux fan doesn't come on, it doesn't mean the system isn't working; it simply means the R/D temp hasn't reached the point at which the switch closes, or about 112 degrees in your case. To check if the A/C is working adequately, you should put a thermometer in the vents and evaluate intake temps and vent temps and get a measure of the cooling effect in the car. Numbers are better than "it doesn't feel as cool as it used to."

To check refrigerant, you could use the sight glass, right there next to the temp switch, as a rough indicator, but the best method is to use gauges and check pressure. The sight glass is okay-ish for R-12, pretty worthless for R-134a.

There's also the "self-diagnosing" option: does the compressor clutch engage when you call for A/C and does the temp drop out the vents? If so, then there's at least adequate refrigerant for the system to run. It might be low, but not too low. (You did say the A/C works, so you already know this.)

If the clutch doesn't engage when you call for A/C, you could try jumpering the connection on the low-pressure cut-out switch, also on the R/D. DO NOT unscrew this, or then you will be low on refrigerant. That might mean you're low, or maybe you have a bad pressure switch. (No need to do this, since you said it works).

The best way is with gauges and someone at least familiar. You can read up and possibly buy a set, not too pricey. Or have it checked at a shop.

That's the problem the vast majority of the time when the aux fan never engages. It doesn't take much of a refrigerant loss before the temp switch fails to trip, even on a hot day in the Valley.

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

I see. I'll take it over to a shop and have them take a look. Hopefully I can get it recharged for a reasonable price. Like I said before, I had a good run. It was last charged in 2006.

__________________
1982 240D - 292,000 miles and counting
Same family for 33 years
Newly rebuilt Monark injectors
Newly replaced clutch
New Bilstein shocks

Hi guys,

So am I correct in understanding that the auxiliary fan is controlled by the A/C refrigerant temp switch alone?

What is the purpose of the aux fan? I always thought it was to keep the engine water temp down. Based on the information in this thread, it would seem that it serves to help the A/C condenser cooler to help with the A/C, and has nothing to do with keeping engine temps down?

My aux fan didn't come on at all. I tested each component, and finally figured out that the PO pulled the fuse out! Everything is wired properly and appears to be working.

Thanks,

PE

__________________
83 240D - 4 speed manual - Manilla Beige
189K miles, Tachometer mod, cool wooden shift knob from PeachParts, CocoMats, Original factory paint, manual windows, manual sunroof. Starting to add AudioWrap to this car too!

I believe the aux fan is only based on the R/D temp in your '83 240D. There is no connection to the cooling circuit, so it doesn't directly keep engine temps down. Indirectly by adding more air to dissipate heat, yes, and people will jumper the aux fan to get this airflow irrespective of the R/D temp.

There might have been differences in older model W123's, so I wouldn't make a blanket assessment about the fan.