Overheat/Aux Fans/AC Issues - Mercedes-Benz Forum
 
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post #1 of 6 (permalink) Old 05-22-2019, 06:22 AM Thread Starter
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Date registered: Jul 2018
Vehicle: 1989 190e 2.6
Location: Alexandria, VA
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Overheat/Aux Fans/AC Issues

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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post #2 of 6 (permalink) Old 05-22-2019, 07:33 AM
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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.
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post #3 of 6 (permalink) Old 05-22-2019, 08:24 AM Thread Starter
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Garage
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Quote:
Originally Posted by dolucasi View Post
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.
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post #4 of 6 (permalink) Old 05-22-2019, 10:54 AM
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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
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post #5 of 6 (permalink) Old 05-23-2019, 07:57 AM Thread Starter
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Garage
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Quote:
Originally Posted by dolucasi View Post
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
I'll take a look this weekend with adding in the resistor.

Any ideas on low speed aux fan being inop?
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post #6 of 6 (permalink) Old 05-29-2019, 06:52 AM Thread Starter
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Garage
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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.
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