Bringing A/C pressures down 300TE - Page 2 - PeachParts Mercedes-Benz Forum

tangofox007 · #16 08-07-2011, 10:31 PM

Quote:

Originally Posted by vstech

...and bad aux fan both it sounds like to me.

Just one problem with that theory: the fan works.

vstech · #17 08-08-2011, 12:24 PM

Quote:

Originally Posted by tangofox007

Just one problem with that theory: the fan works.

fan works ONLY on high speed.
and after WAAAAY too much heat into the system.

vstech · #18 08-08-2011, 12:25 PM

Quote:

Originally Posted by ps2cho

The bad aux fan not coming on low would be one those sensors? I know there are two...which one is it?

I'll evac system again, replace R/D, replace x switch and refill to 850g then. Will report back in a few days.

I would fill to 750 and adjust until pressure and temps climb to where you like them.

tangofox007 · #19 08-08-2011, 12:34 PM

Quote:

Originally Posted by vstech

fan works ONLY on high speed.
and after WAAAAY too much heat into the system.

Both of those factors point to a control problem, not a "bad aux fan."

Quote:

Originally Posted by vstech

overcharged, and bad aux fan both it sounds like to me.

vstech · #20 08-08-2011, 12:41 PM

correct. bad aux fan resistor, I should have said...

compu_85 · #21 08-08-2011, 01:41 PM

I wouldn't go so far as to suck all the charge out. I'd remove a bit at a time until things settle in. (I might be wrong here and VSTech will probably correct me

) First I would get that aux fan working properly.

For the time being you could probably jumper the resistor so the fan just runs on high speed. I'm going from memory here... I think both speeds for the aux fan get power the same strip fuse so that won't create an overload. I'll double check that.

EDIT: According to the ETM both speeds get their power from the 16 amp fuse D. You should be ok just jumpering the resistor for now.

I'm trying to find the component locations section on the W124 service CD, but it's hiding. On the W126 it's in with the ETM... \

EDIT AGAIN: Looking in EPC, the resistor probably lives somewhere up by the driver's side headlight. Here is the part on fastlane.

-J

ps2cho · #22 08-08-2011, 02:48 PM

Ahh so it could be a bad resistor then, so not necessarily the A/C switch on the drier.

Is there a way to test resistor via resistance? I got one ordered regardless though. Should be here in the next day or two then I'll let you know if the fan kicks on at anything other than high speeds.

compu_85 · #23 08-08-2011, 03:09 PM

If the resister has no resistance you need not resist the urge to remove it and reassign it to the recycle bin.

Use a meter, if it's open (infinite resistance) it's bad.

compu_85 · #24 08-08-2011, 03:12 PM

If you just jumper out the resistor for now that might help you get the charge right... it will make more airflow over the condenser.

-J

ps2cho · #25 08-09-2011, 06:49 PM

I removed the resistor today....my DMM was reading I guess ~0.8ohms between the contacts....couldn't really get a completely accurate reading though, it was going all over the place at some points randomly.

Got the new one coming from UPS by the end of the day anyway, was just interested.

I'm hoping that does the trick.

ps2cho · #26 08-09-2011, 08:21 PM

Got the new one in....still only high. No change.

FYI though -- This has to be A/C related because coolant temp was only @ 81C when the high speed kicked on. It was zero to high though. No low speed. So the aux fan A/C side IS coming on, its not the coolant temp circuit here. Its just I have no low speed.

I disconnected the connectors at the green switch and jumpered them with ignition on and the fan did not start -- is this normal or?

Does my issue point to the high/low pressure switch being faulty?

ForcedInduction · #27 08-09-2011, 10:36 PM

Quote:

Originally Posted by ps2cho

I know the system is not overcharged because I evacuated the system a few times, then charged by weight again.

It is overcharged. Do you know how much oil was removed and injected?

ps2cho · #28 08-10-2011, 09:29 AM

Evacuation should not remove any oil, so none.

What would be considered normal pressures on a 105F day?

vstech · #29 08-10-2011, 10:57 AM

evacuation shouldn't remove much oil, but removing REFRIGERANT will certainly take out an oz or two...
I've explained to you that the system has too much 134. take out some. I'd remove 150 or so grams and see what it reads.

vstech · #30 08-10-2011, 11:02 AM

Quote:

Originally Posted by ps2cho

I was having some A/C issues a few days ago when a valve stem was bad...Replaced it, evac'd system, recharged, but I noticed that my pressures are really high...

r134a
105F Ambient
Low side: 65psi
High side: 340psi (aux fans kick on at this point and bring it down to ~290psi)

ok, if your suction is over 50psi there is a problem. if the head is over 300 psi there is a problem.
please remove refrigerant.
it's not necessary to remove all, evacuate and recharge, but you need to get your pressures down.
inexpensive recovery tanks are available to legally remove R134... but get the suction below 50psi. and even on a 105 day, the head should not be over 300.