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Overheat/Aux Fans/AC Issues

2K views 8 replies 4 participants last post by  GaryStofer 
#1 ·
Got some issues I think may be combined and want to see the correct order to fix these things. My car tends to get hot (close to overheat) when idling which is fairly common from what I've seen but want it fixed.

AC has some pressure (not sure its enough)
AC also has a leak I'm 90% sure
Low Speed Aux Fans Dont Ever Run
High Speed Aux fans kick on at 102c and cool down the engine properly
AC Compressor works and does send cool air through the vents until I get above about 85-90
Car will rise to 102c idling without the AC on on a hot day

I replaced the low speed aux fan relay and the ceramic preresistor, one of my aux fans was dead and that was replaced earlier. Can confirm both work perfectly on high speed mode.

1) Is the rising to 102 without ac on a hot day abnormal? Should the car stay below that even without ac on on a 90f degree day? Should I just go ahead and do a coolant change and/or what else to check here?
2) Should I have a shop fix the ac leak, vac and refill the system first or
3) Should I first track down the low speed aux fan issue?

I'm assuming the compressor is kicking off when the car gets hot and thats why I lose ac at higher temps. Just wondering which part of this to start working out first. I am kinda stuck on the low speed fan, any thing else to check there?
 
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#2 ·
Lots of questions there to address.

(1) Is it normal to hit 102c idling at 90F outdoor temp without AC operating?

- Yes on a 30 year old car. Sometimes people blame the regular fan clutch for not operating properly, sometimes radiator is blamed for not allowing enough coolant flow at idle, etc.
- If I were you I would just lower your electric fan trip temperature to be something like 95c. You can add a 1.2K ohm resistor in parallel to the temp sensor on the cylinder head. Works pretty well.

(2) AC refrigerant leak.

- Is yours converted to R134 or is it still R12?
- In either case check your high pressure hose for wetness. If it is wet, read my post on the matter for a quick fix that will only cost you $10. Mine has stopped leaking with that temporary fix.
 
#3 ·
Lots of questions there to address.

(1) Is it normal to hit 102c idling at 90F outdoor temp without AC operating?

- Yes on a 30 year old car. Sometimes people blame the regular fan clutch for not operating properly, sometimes radiator is blamed for not allowing enough coolant flow at idle, etc.
- If I were you I would just lower your electric fan trip temperature to be something like 95c. You can add a 1.2K ohm resistor in parallel to the temp sensor on the cylinder head. Works pretty well.

(2) AC refrigerant leak.

- Is yours converted to R134 or is it still R12?
- In either case check your high pressure house for wetness. If it is wet, read my post on the matter for a quick fix that will only cost you $10. Mine has stopped leaking with that temporary fix.
Everything seems to be operating correctly aside from the aux fan low speed. I did see where you can simply buy a lower temp sensor so might try that.

Converted to r134 at some point. When I bought the car last summer there was some AC, after winter I had nothing and after a can of refrig. its "working" again. Found what looked to be refrig. on the plastic panel under the engine so assuming there's a leak there somewhere.
 
#4 ·
Check my post for the AC. Yours is also a '89 that got converted. Puts to much pressure on the high pressure hose that is aged.

See if you have the exact same problem. My band-aid worked so far.

Idle coolant temp. - it is wise to power the fan temp from 102c to about 95c. Not much lower as it will run too much.
It is best to just put the resistor in and adjust the value to your liking with the value of that resistance. Mine turned out to be 1.2Kohm.
Yours maybe slightly different.
With all the tolerances needed, you are basically fine tuning the cooling system specific to your car. So it will be custom trimmed for you.

- Cheers
 
#6 ·
She's now working well, at least for the time being. Had a local shop properly refill the refrigerant and after a quick test drive today the low speed fans kicked on and after sitting in 80 degree heat idling for 5 minutes the car had no intention of getting above 85-90c. That said there's definitely an ac leak and the shop can't find it so we'll have to see what happens but at least for now everything is working right and not overheating.
 
#7 ·
Hi there. I would like to ask a question on the Coolant temparature sensor issue please. Got a w124 with a M102 (2.3) engine. South African model. I need to Identify the Coolant temparature Sensor on the car. I just bought it as a 'Project'. The car apparently overheated because of fan issues caused by the previous owner trying to disable the alarm. The cylinder head was stripped and repaired by a local "Expert" but the sensors are all suspect and have been left in a plastic bag in the boot.
Any advise will help.

Thanks from Sunny South Africa
 
#9 ·
Hi,
I fixed the nearly overheating problem once and for all !!

The thermo switches that operates the magnetic fan clutch and the aux fan are both in a single sensor mounted front left corner of the cylinder head on the earlier models and in two separate sensors for later ones. For the RED colored dual sensor/switch the magnetic clutch switch closes at 105 deg C and opens at 100degC while the secondary AUX fan comes on at 115 and goes off at 105. On the dashboard temp display that's just a hair under red line, and it is very concerning to the observant driver. Also at those temps the oil pressure at idle starts to head to very low indications.

The fan clutch and AUX fan (half speed) also get triggered by a pressure switch in the AC system. There are two pressure switches on the AC-dryer bottle, just behind the left headlight, one is for the fans. Both fans come on when there is enough pressure in the AC system to start working, independently of temperature. While this system works assuming the AC unit is functioning and the driver turns it on, it doesn't when the AC unit is out of gas or otherwise disabled. Then there is no fan cooling while sitting in traffic until the very last minute, just before boil over.

Having had this issue in California stop and go traffic and not being able to find a source for a replace thermostat with lower set points, I made an electronic thermostat that gets its input from the temp sensor which runs the dashboard gauge. It control the fans by means of the AC pressure circuit by paralleling that switch . The electronic thermostat is adjustable so I can set it to kick in at 90C and go off at 80C for example. Oil pressures and drivers are much happier now...

If there is enough interest in this I could make some boards and instructions for others, parts cost maybe about $30..

Gary S
 
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