AC Questions - PeachParts Mercedes-Benz Forum

Stevo · #1 04-23-2010, 07:58 PM

On a July road trip through the Ca central valley I stopped to get my AC charged at a shop that only worked on MBs, (mostly older ones

) The owner seemed like a very knowledgeable guy and now I'm wondering about something he said...."with the new refrigerant the auxiliary fan should run when ever the AC is on".

We dont need AC around here so its not something I know much/anything about.

I ask this because I was doing a search on why the fan on my, new to me, wagon didn 't come on when I turned the AC on, DOH, cause its not spoz too

, The wagon still uses R12 and works good, but what about the fan always running with the AC when using the new R 134, as the indy told me. (about my sedan)

Also while searching I saw where someone mentioned this 'fan thing with R 134", No one came back, any new input??

leathermang · #2 04-23-2010, 08:12 PM

I believe his statement to be essentially correct.
In dealing with an old car... a few bent fins in the condensor, a little dirt and corrosion on the fins, and a 20 percent drop in efficiency due to R134a's molecular phase change heat absorption abilities compared to R12 it will probably stay on in most situations where you would be running the AC just to hit the marks established by the pressure switch, temp switch, and ' pilot operated' switch indicating the amount of cool you want in the compartment.
Many people hard wire it to stay on when the AC is on.. which I think is a good deal even with R12 if you are in the South or SouthWest....
That is not to say that where you live it might not be on all the time because your ' draw' may not fulfill the need for that extra help in terms of ' air across the condensor'.. but that IS the bottle neck of ALL AC systems... so causing it to stay on if there are problems is the first and most logical system change to accomplish moneywise.

#3 04-23-2010, 08:57 PM

On most cars, the fan is turned on by a high pressure switch. It's purpose is to blow air across the condensor to bring down high side pressure. When converted to 134, the high side pressure runs higher, thus turning the fan on more often.

If the fan is not coming on, that means that you do NOT have excessive high side pressure which is a good thing.

engatwork · #4 04-23-2010, 09:00 PM

a/c season is coming up and here come the questions

. Good to see ya'll around for another season.

#5 04-24-2010, 08:41 AM

Yep, it's ground hog month.

Stevo · #6 04-24-2010, 09:36 AM

Yah, AC questions in the spring and GP questions in fall

OK thanks Greg, I will wire both cars so the fan stays on when the AC is on. I have a couple spare aux fans laying around in case I ware one out

Thanks, I knew you guys down south would know the "AC scoop"

#7 04-24-2010, 09:32 PM

Why do you want the fan on all the time? Are you having overheating problems? It sounds as if it's working as designed.

leathermang · #8 04-25-2010, 12:10 PM

One thing that hard wiring it on does it provide an indication of problems hopefully before you are in a really bad need of it turning on... if you have it turn on all the time... then the first time there is some problem with it you know you need to address it.... but otherwise you can be IN the emergency heat situation before you have any knowledge there is a problem.

Stevo · #9 04-25-2010, 01:23 PM

Quote:

Originally Posted by leathermang

One thing that hard wiring it on does it provide an indication of problems hopefully before you are in a really bad need of it turning on... if you have it turn on all the time... then the first time there is some problem with it you know you need to address it.... but otherwise you can be IN the emergency heat situation before you have any knowledge there is a problem.

It sounds to me like hard wiring the aux fan when using 134 is a good practice, why not?.. all I can think of would be a possible needless use of power, epically with a 240D. When using R12 your reasoning sounds good enough for me, epically for someone that rarely uses AC, like me. Also with a 617 theres a little more hp and how much draw would the fan take anyway.

leathermang · #10 04-25-2010, 03:21 PM

Power means nothing down here if your body is HOT.....

Stevo · #11 04-25-2010, 05:30 PM

Thats it, ..even more so as time goes by

vstech · #12 04-25-2010, 05:32 PM

um, if you're hot, the ... 134 is not working well in the car.
dump it, flush the system, replace the expansion valve, and recharge with R12.
bobsyouruncle, it's cool!

leathermang · #13 04-25-2010, 06:22 PM

vstech, we were talking about the power drain on the puny 240 engine... and I was saying better to use that power to run the AC compressor than to be HOT... I can spare the power...but not the cool...

Scott98 · #14 04-25-2010, 07:15 PM

Quote:

Originally Posted by leathermang

vstech, we were talking about the power drain on the puny 240 engine... and I was saying better to use that power to run the AC compressor than to be HOT... I can spare the power...but not the cool...

I got in my 240D one morning, started it, turned on the A/C compressor and the strain from the compressor killed the engine.

Scott

vstech · #15 04-25-2010, 08:42 PM

Quote:

Originally Posted by leathermang

vstech, we were talking about the power drain on the puny 240 engine... and I was saying better to use that power to run the AC compressor than to be HOT... I can spare the power...but not the cool...

I gotcha on your one response, I agree. but the majority of this thread is about the use of the aux fan and it's power drain on the engine. my response is in that regard. if you are needing cool, and you want a 240D, you should have R12. doing things to make 134 work is a waste of time and money. and it'll never cool as well or as efficiently as R12.