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| texas993 Member Date registered: Oct 2013 Location: Dallas, TX Vehicle(s): 2005 G500, 1995 E300D, 1987 560SL Posts: 24 | Help needed with Aux Fans and AC I have searched every corner of the internet for a solution.... My 2005 G500's AC is not cooling well under certain conditions. When the outside temps are moderate - 70s to 80s - and the vehicle isn't moving, it doesn't blow cold air. When the engine heats up, the high speed aux fans kick in and the AC works well. AC works fine if the car is in motion. (Air passing through condenser) I think the issue is the aux fans are not turning on "low" speed. Should the fans be on anytime the AC is switched on? A few facts: AC system is properly charged Compressor seems to work - when high aux fans are activated the system cools well. Difficult to tell if compressor is "on" as there is no fan clutch switching on/off. Aux fans come work fine when directly connecting to 12V battery No voltage reading on the connectors to the aux fan (unplug the aux fan, take a reading from the wiring harness, 0 volts) I pulled the aux fan relays under the center console and swapped them - thinking they wouldn't both go bad at the same time. No change. I removed the CCU and cleaned with electronics cleaner spray. This was giving me issues last year - dusty CCU - and when I cleaned it the system worked fine. I am still suspicious of it. But all functions work fine when moving to various outlets, changing temp, fan speed, etc. While I have owned this truck for 5 years and it has worked well, the only electrical issues that I have had (besides cleaning the CCU) is the seat switches on the door. The truck spend several years in dusty west Texas and dust got into those switches, causing them to act irrationally. Cleaning them eliminated the problem. 100k miles. Please help! I really don't know where to go from here. For years, the AC worked well and was freezing in TX! Thanks in advance! | ||
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| Floobydust Veteran Date registered: Mar 2014 Location: Massachusetts, USA Vehicle(s): 1995 E320 Cabrio, 2003 G500, 2000 SL500, 1980 TR8 Posts: 284  | RE: Help needed with Aux Fans and AC I had a similar problem when I first got my G and it turned out that the fan control fuse (in the fuse panel on the left side of the dash) was blown. Did you check it? As far as I know, the fans run at high speed in association with the A/C systems (they pretty noisy too). Edited by Floobydust 4/28/2018 4:05 PM | ||
| #239031 - in reply to #239030 |
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| texas993 Member Date registered: Oct 2013 Location: Dallas, TX Vehicle(s): 2005 G500, 1995 E300D, 1987 560SL Posts: 24 | RE: Help needed with Aux Fans and AC Floobydust - 4/28/2018 4:04 PM I had a similar problem when I first got my G and it turned out that the fan control fuse (in the fuse panel on the left side of the dash) was blown. Did you check it? As far as I know, the fans run at high speed in association with the A/C systems (they pretty noisy too). I have NOT checked that yet. Duh, check the easy stuff first. I'll look at it tomorrow and report back. I also learned how to jumper the relay slot. That should give me some info too. | ||
| #239032 - in reply to #239031 |
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| texas993 Member Date registered: Oct 2013 Location: Dallas, TX Vehicle(s): 2005 G500, 1995 E300D, 1987 560SL Posts: 24 | Re: Help needed with Aux Fans and AC Fuses were all fine. I jumped the fan relays and they both came on fine. Tested the freon pressures and they are fine. I am really thinking it is the CCU. I'll order a new one and try it out. ($340 from OEDiscountparts.com) | ||
| #239043 - in reply to #239030 |
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| JCH4 Regular Date registered: Jun 2010 Location: Charleston, SC Vehicle(s): 2003 G500, LR 1972 IIA, LR 1962 IIA, Husqvarna 350 Posts: 99  | RE: Help needed with Aux Fans and AC Please let me know what happens. I have this same problem and summer is upon us. Works great when rpms are high but stinks when at idle or in slow city traffic. | ||
| #239052 - in reply to #239030 |
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| texas993 Member Date registered: Oct 2013 Location: Dallas, TX Vehicle(s): 2005 G500, 1995 E300D, 1987 560SL Posts: 24 | Re: Help needed with Aux Fans and AC New CCU did not fix the problem. In fact, it made it worse - with the new ccu, I could only get air from the floor vents. It is a genuine MB part ordered new from a dealer. I'll be returning it. So back to the beginning on the AC issue. Let me re-group and come up with a plan. Could be an erratic compressor or something electronic. When the system is running, the freon pressures are good. | ||
| #239079 - in reply to #239030 |
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| DUTCH Administrator Doppelgänger Date registered: Apr 2006 Location: US, GA, Atlanta Vehicle(s): 2015 Audi Q7 3.0 TDI,2018 Sprinter Posts: 9963  | Re: Help needed with Aux Fans and AC texas993 - 5/7/2018 6:11 PM New CCU did not fix the problem. In fact, it made it worse - with the new ccu, I could only get air from the floor vents. It is a genuine MB part ordered new from a dealer. I'll be returning it. So back to the beginning on the AC issue. Let me re-group and come up with a plan. Could be an erratic compressor or something electronic. When the system is running, the freon pressures are good. It might be worth evacuating the system, pulling a hard vacuum for 60 minutes and then refilling with the exact WEIGHT of R-134. Forget about the pressure readings. Then see how it runs. | ||
| #239080 - in reply to #239079 |
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| texas993 Member Date registered: Oct 2013 Location: Dallas, TX Vehicle(s): 2005 G500, 1995 E300D, 1987 560SL Posts: 24 | Re: Help needed with Aux Fans and AC DUTCH - 5/7/2018 7:05 PM texas993 - 5/7/2018 6:11 PM New CCU did not fix the problem. In fact, it made it worse - with the new ccu, I could only get air from the floor vents. It is a genuine MB part ordered new from a dealer. I'll be returning it. So back to the beginning on the AC issue. Let me re-group and come up with a plan. Could be an erratic compressor or something electronic. When the system is running, the freon pressures are good. It might be worth evacuating the system, pulling a hard vacuum for 60 minutes and then refilling with the exact WEIGHT of R-134. Forget about the pressure readings. Then see how it runs. Alright, worth a shot. | ||
| #239082 - in reply to #239080 |
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| DUTCH Administrator Doppelgänger Date registered: Apr 2006 Location: US, GA, Atlanta Vehicle(s): 2015 Audi Q7 3.0 TDI,2018 Sprinter Posts: 9963 | Re: Help needed with Aux Fans and AC texas993 - 5/7/2018 8:24 PM DUTCH - 5/7/2018 7:05 PM texas993 - 5/7/2018 6:11 PM New CCU did not fix the problem. In fact, it made it worse - with the new ccu, I could only get air from the floor vents. It is a genuine MB part ordered new from a dealer. I'll be returning it. So back to the beginning on the AC issue. Let me re-group and come up with a plan. Could be an erratic compressor or something electronic. When the system is running, the freon pressures are good. It might be worth evacuating the system, pulling a hard vacuum for 60 minutes and then refilling with the exact WEIGHT of R-134. Forget about the pressure readings. Then see how it runs. Alright, worth a shot. If you lose any compressor oil in the process, you might want to put some back along with the R-134. Have you watched the sight glass on top of the A/C Dryer. It should show bubbles for a few seconds right after the compressor starts, and then be bubble free. Also, in your previous post you mention that you only had cooling at your feet. Are you sure that all of your blend flaps are working correctly? | ||
| #239085 - in reply to #239082 |
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| texas993 Member Date registered: Oct 2013 Location: Dallas, TX Vehicle(s): 2005 G500, 1995 E300D, 1987 560SL Posts: 24 | Re: Help needed with Aux Fans and AC Dutch. The cooling at the feet issue was only when I put in a new CCU. When I install the old CCU, it functions normally and I can get air at all vents. I'll keep y'all posted as I will hopefully get some time to work on it throughout the week. | ||
| #239090 - in reply to #239030 |
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| texas993 Member Date registered: Oct 2013 Location: Dallas, TX Vehicle(s): 2005 G500, 1995 E300D, 1987 560SL Posts: 24 | Re: Help needed with Aux Fans and AC Update: I put all the car back together, intending to take it to a shop for repair. Then I remembered Dutch's suggestion to evacuate the system and refill to the factory spec. I did that and it worked! While vacuuming the system, I heard a slight "pop", the vacuum gauge jumped, then continued decreasing positive pressure then creating negative pressure. I wonder if the expansion valve or some other sensor became unstuck with the vacuum. Either way, the system is working fine now with the old CCU. My original thoughts were that the Aux fans weren't working therefore not cooling the condenser. Wrong, the system wasn't pressurized properly, despite good gauge readings. Upon refilling the system, the aux fans kicked on as they should. Hopefully this is the end. If not, I'll suspect the expansion valve next. Thanks for the insight and help. | ||
| #239206 - in reply to #239030 |
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| DUTCH Administrator Doppelgänger Date registered: Apr 2006 Location: US, GA, Atlanta Vehicle(s): 2015 Audi Q7 3.0 TDI,2018 Sprinter Posts: 9963 | Re: Help needed with Aux Fans and AC Thanks for the followup with your success! Happy Trails! | ||
| #239208 - in reply to #239206 |
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| texas993 Member Date registered: Oct 2013 Location: Dallas, TX Vehicle(s): 2005 G500, 1995 E300D, 1987 560SL Posts: 24 | Re: Help needed with Aux Fans and AC UPDATE: I continued to have issues with the AC cooling. Particularly when the car and exterior temps were not too high. Since I am still recovering from an injury and wasn't able to fix it myself, I took it to a shop for diagnosis and repair. It turns out the compressor was going out. It is a variable speed compressor and the lower speeds were not working. Or so I was told ... I replaced it with a MB compressor and drier. Stupid labor cost ... but bought the parts on my own (shop was not willing to discount - but was ok with me bring in MB parts). Seems to be working fine now. So, it appears that these compressor die a slow death. Now on to the $600 wiper motor that has gone bad... | ||
| #239635 - in reply to #239030 |
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