Very hot 300TE with Low (& High??) electric fan cooling problem

Guys

I have been reading quite a few threads since my temp gauge went to 120+ in traffic a couple of days ago (ambient temp was 32C or about 95F). I tried to get the fans to come on by turning on the A/C but they refused, so I managed to lower it by turning down some side streets & getting some air through the radiator. (I added this to another thread but it occured to me that it might be better to post a new thread)

A/C works well & the belt driven fan clutch was renewed last year & seems to be working OK.

I've tried to do some tests and so far today (35C) I have had 1 fan come on high at about 95-100C (temp gauge) with the A/C on a short trip (right side looking at it from the front - your driver side - my passenger side).

Later I removed the Temp guage connector (which looked a bit beaten up) and the same fan came on high, but nothing from the other one.

When I bridged the plug I heard relays switching near the fusebox & near the A/C drier but no Low fan came on - in either of the fans.

I also tried bridging the each side of the Low fan resistor with 12v - but nothing happened either side. Though I may not have done this correctly?

Does this mean -
I have at least 1 fan that's dodgy;
I possibly have a Resistor that's stuffed;
Possible other problems...

Any help greatfully accepted.

PS - something else I was wondering is that when all of the R12 was replaced with R134a a few years back, how does this affect the psi readings from the A/C for the Low speed fan? Are they close enough?

Cheers

Stu

[david s poole]

g'day mate,if you run the a/c the aux fans should come on almost immediately.sounds like one of them is burned out and the extra amp demand may be causing the relay to work erretically.i lived in elizabeth back in the sixties and have been in dallas since 78.by the way the radiators in those cars could cause problems when they got old with the symptoms of climbing temp while sitting at idle and then coming back down as the engine was speeded up.

[Arthur Dalton]

There are two fan circuits High and Low

The high fan comes On @ 105C..that is the fan sensor that you unplugged . It defaults to high fan when unplugged, verifying that circuit.
With that test, if both fans have to come on..if only one does, you have a bad fam motor.
If the low fan [ a/c ] does not come On with a/c on a hot ambient condition, then the refrig level may be slightly Low.
The test for low fan is to jumper the sensor at the drier ..the sensor that has the pigtail wires , NOT the spade connectors. If YES, then low refrig is most likely..if NO, then check the fuse for Low Fan if the relay is clicking w/jumper

The 12v to resistor test is with a jumper wire from battery pos terminal to resistor.. One side of R will give you low fan , the other will be high fan. That jumper test by-passes all sensors and relays, so it is fan motors test only

Thanks for that David & Arthur!

(& sorry for the other post - I thought I better try starting one myself after I'd already posted that one...)

I was having issues sorting out which sensor to disconnect for High aux fan but finally found it before I posted last night.

I think I have worked out which pigtail terminals to jumper to test low aux fan. And where those annoying relays are. I'll check these tonight.

The rest of the system is hopefully OK - I replaced the radiator, thermostat, fan clutch, & everything in the A/C last year - I figured you can't muck around when its 45C outside...

Thanks again.

PS - David - don't know if you'll care but the Dogs won the footy again this year beating the Bays, but the only stuff in the paper now is about the Adelaide United soccer team playing off in the Champions League tonight.

I jumped the pigtail connections near the drier earlier and confirmed that the Low fan aux circuit came on (at least in 1 fan). It didn't sound/feel much different to the High fan test I repeated.

I let the car idle until it was showing somewhere over 110C (ambient 34C), but no aux fans cut in either high or low - with or without the A/C on.

The A/C seems OK but I'm going to get the refrig level checked anyway - probably Saturday.
I will check the Thermistor resistance values tomorrow as its mainly the High fan fail safe - or lack of thats bothering me.
I'll have a go at repairing/replacing the dodgy fan on the weekend.

Does that sound like a reasonable course of action? or any other suggestions?

[Arthur Dalton]

If you have high fan when you unplug the blu sensor, but it does not come on when the coolant temp gets to 105/107, then the sensors values are off spec. A new sensor will work..
There is also a modification we do by putting a resistor across the sensor that allows the cut-in spec of the sensor to drop to around 100C..you may want to do that.
Search Archives.
There should be a distinct difference from low/high speeds, so if you do not see that, then the fan motor is suspect, along with the other bad one.
Another trick is to put a cabin on/off toggle switch across the wires I had you jumper to test for low fan..that allows you manual control of the fans from the cabin..cheap mod and comes in handy when you run into overheat condition like you did the last time.
Both fans must run, so start there.........sometimes the brushes get crap in them and a sharp blow at the blade fron hub w/rubber hammer will get one going again

[Stu17]

Originally Posted by Arthur Dalton

If you have high fan when you unplug the blu sensor, but it does not come on when the coolant temp gets to 105/107, then the sensors values are off spec. A new sensor will work..
There is also a modification we do by putting a resistor across the sensor that allows the cut-in spec of the sensor to drop to around 100C..you may want to do that.
Search Archives.
There should be a distinct difference from low/high speeds, so if you do not see that, then the fan motor is suspect, along with the other bad one.
Another trick is to put a cabin on/off toggle switch across the wires I had you jumper to test for low fan..that allows you manual control of the fans from the cabin..cheap mod and comes in handy when you run into overheat condition like you did the last time.
Both fans must run, so start there.........sometimes the brushes get crap in them and a sharp blow at the blade fron hub w/rubber hammer will get one going again

I am actually the OP and just wanted to thank those guys. I couldn't at the time due to some IT issues.
The fans and sensor did get sorted because of them. (The low speed of the fans decreased when both were working...).
Also by putting a 1.1K resistor across the blue sensor, the emergency cut in temperature is much lower - less than 100C. Loved the price of those resistors - 45c for a pack of 8.

Cheers
Stu
1992 300TE

[Cal Learner]

Glad to hear you got it sorted out. Many of us have learned that Arthur was the "go-to" guy for aux fan issues. BTW, I'd like some of that 34C weather right about now. "Sunny" Northern California where I am is actually foggy, rainy, chilly. Maybe I'm just in the wrong part of the world?