This will kind of rambling because my head is starting to spin. I am beginning to think the PO disconnected because he could not figure out what was wrong.

It started when I was working on getting the AC going on my new to me 93 940 (built 7 92). Somehow I got the compressor going from a possibly stuck position. I attempted to refill the system but either my low mechanical aptitude kicked in or there is a big leak. I retreated from that and made an appt at a friend's AC shop to get it going from my progress.

While doing this, the car appeared to overheat with coolant wanting to push out of the overflow. I noticed the fan was not going. I had never had the problem before this time. The only difference between this idling session and others was I had the compressor running via a jumper at the low pressure cut off switch. Is there some correlation?
I have spent quite a bit of time in the FAQ sections. The fan spins freely. I find neither wire going to the temp sensor in the upper right radiator with the engine off or on. I cant jump it from there by connecting it to teh battery direct. jumping both leads together does not do anything. The car did sit for four years. I cleaned the ground on the front wall by the battery. IS there a way to see how the cooling relay is working? (course you have to take the battery out pretty much).

One issue I have with the FAQ, is there are many references to early and late 940's with man important differences in AC and cooling. Is there a way to quantify what the breakoff is?

When I was going over the AC, I found the three switches down on the bottom of the evaporator (the high pressure etc) all disconnected (probably the DPO by my guess. Was he dealing with over heating and sacrificed the AC to keep the car running rather than fix the problem?
Sorry to be so rambling but I have been so involved under the hood of this car that I was getting a headache. I will need to buy beer for lots of people out there when this is done.

It sound like you have two separate problems - non working A/c AND overheating engine. I think I would tackle the engine cooling first. Make sure the thermostat is opening when the temp gauge approaches mid point. A rapid increase in upper radiator hose temperature is generally a good indicator that the thermostat has just opened.

If it still overheats check the radiator for free flow - no obstruction.

I assumed the overheating problem was due to no cooling fan but I will check out the hose. I did grab an infrared thermometer and found the radiator to be hot, mostly up near where the top hose comes in so I assume the rad works.

...and think about on the Fan Control relay down in front of the radiator. It should have constant 12V from the Battery on both the High and Low speed coils. Both of them just waiting for a ground from 1 of 3 sources:
High Speed...
1) Radiator thermo-switch, 2) Gray pressure switch on condenser
Low Speed...
3) Brown pressure switch on condenser
[the other (purple) switch there is an excessive pressure cut-out in the clutch circuit, so if it's unplugged, there is no way to get 12V from the Low side switch to the clutch.

Since shorting the 2 radiator switch wires* didn't get the fan going, it's good bet there is no voltage to those coils (or thru the HS coil to the rad sw). My son had that problem on his '92 940 and it turned out to be a Gray Fusible Link wire leading from the battery + terminal. I'd say start there.

I was "helping" him by phone, despite which he found the FL (after slitting the outer wire sheath) burned open at the end (about 10" or 12" away). Remember, I never saw this, so I can't describe exactly how that connection is made or was fixed. But he repaired it by cutting the last inch or so off and reattaching the rest of it, which then allowed the fan to run when the radiator switch closed.

BE SURE to disconnect the Negative battery cable before getting into the Positive wiring. I think you'll find 3 or 4 smaller wires at the + terminal besides the big cable to the starter. The Fusible Link will be a thickish gray one.

*"jumping both leads together does not do anything."

THIS confused me:
"I find neither wire going to the temp sensor in the upper right radiator [HAS VOLTAGE?] with the engine off or on." That's what you meant, right?
Otherwise "jumping both leads together does not do anything".doesn't make sense to me.

ALSO: The Fan relay can be unclipped from is mounting and pulled up a bit, if you need to check voltage or operation more closely.

ALSO #2: If your jumping the AC clutch is what's causing the overheat (with no fan), pull the Fan back or out and flush water thru from the front. My son's '92 radiator was really full of crap, and most of the lower fins had perished as they say. Didn't take much to get the Fan on till he put in a new radiator.

"later" 940's may refer to the introduction of factory R134a AC in the '93 940. My son's '92 had been converted to R134a according to underhood labels.

--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Bruce,

I recently swapped my 90 744 (both elec and mech fans) for a 92 745 (elec. fan only) and find your post valuable in explaining the fan logic. Does it appear in the FAQ's? If not, I think you should send it to Steve R for inclusion. I'm sure many others would like it.

You said "...#2: If your jumping the AC clutch is what's causing the overheat (with no fan), pull the Fan back or out and flush water thru from the front..." How about "from the rear"?

"I...find your post valuable in explaining the fan logic."

Thanks, Chris. If you mean just the messy first paragraph, I'll try to clean it up below...
--------------------->

Engine Cooling Fan Control (based on '93 940 wiring)

The Fan Control relay down in front of the Battery should have a constant 12V coming in from the Battery (fusible link) at Terminal 1A. This 12V is routed internally to the relay's High and Low speed coils. Either coil can be energized by a grounding wire from 1 of 5 sources:

High Speed Coil Ground - white/black wire from either:
1) Radiator thermo-switch
2) Gray pressure switch on condenser
3) LH2.4 ECU pin 11 (on cars so-equipped)

Low Speed Coil ground - Blue/Black wire from either:
4) Brown pressure switch on condenser
5) LH2.4 ECU pin 10 (on cars so-equipped)

NOTE: The Fan relay's internal circuitry allows only one coil to be energized at a time, with the High speed coil having top priority.

<------------------------
That reads better to me. Or did I muck it up?
If it's OK, you have my blessing to give it to Steve.
Or give me your edit input if I overlooked something.








--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Sounds like the thermostat is OK. The radiator flow may still be in question though. Removing upper and lower radiator hoses and running a garden hose in the top will tell you if it has good flow through to the lower hose.

Does it overheat even on the open road like cruising at 45+ ? In that environment the fan doesn't do much even if it does work right, so overheating in that situation is likely caused by a problem somewhere else in the cooling system or something else with the engine like the ignition timing.

I do agree that you need to get the fan working if it isn't. Sorry if I wondered off track.

The only time I got over heating was when I was idling in the driveway with the Compressor jumped. I have had the car idling in the driveway many times in the last 2 weeks in hotter weather with no issues. It only over heated once and it was the only time I had the AC compressor running. In the FAQ, it says the cars are more susceptible to over heating with the AC on. I had two problems from what I saw.
1.) No fan came on despite the coolant pressuring out of the reservoir.

2.) The gauge in the dash did not appear to show the car being hot.

The FAQ seems to discuss the inter-relation between the AC and the cooling system but I believe the discuss this mostly in reference to later 940's which I do not know where teh break off is.