AC troubleshooting assistance anyone? (r134) - Page 2 - PeachParts Mercedes-Benz Forum

BillGrissom · #16 09-03-2014, 04:31 PM

The outlet of the condenser should not be too hot to touch, regardless of charge and such. When too hot in my cars, I also get tepid cooling from the vents. When I had that in my 300D, I manually actuated the radiator fan (jumpered 30 to 87 in relay base), then the liquid tube cooled greatly and cold air blew. It seems my AC temp switch (on filter/drier) trips too high (both 300D's).

I had a similar issue in my 2002 T&C many months after replacing the AC compressor (Nippondenso, similar to Sanden). The compressor was also making noise. Nothing I did w/ refrigerant charge or such gave good cooling at idle and the liquid tube was too hot. I took the compressor apart and found the rebuilders had assembled it incorrectly, with 2 outlet reed-valve plates stuck together on one side and none on the other. It had only been working initially because the backer plate had been serving as a reed plate. After I re-assembled correctly, no more noise and cooling is great. There are youtube videos showing disassembly and say "almost impossible to re-assemble wrong", but these bozos managed. If it comes to that, don't be afraid to look inside your Sanden.

vstech · #17 09-03-2014, 06:03 PM

It SUCKS to put a small pf condenser in a big car with an expansion valve, and no accumulator. Forces the system to poorly operate... It's all a compromise. Throw in too big a compressor, and pressures go bonzo... I think the 5 piston SANDEN may be better suited for these cars... Likely too small, but functional... With the pf...

RavenTBK · #18 09-05-2014, 03:35 PM

Quote:

Originally Posted by vstech

It SUCKS to put a small pf condenser in a big car with an expansion valve, and no accumulator. Forces the system to poorly operate... It's all a compromise. Throw in too big a compressor, and pressures go bonzo... I think the 5 piston SANDEN may be better suited for these cars... Likely too small, but functional... With the pf...

So, I gather I should pick up an accumulator and hack it into the system? Any particular type to look at?

What about adding a second 16x20 PF in series as the single one I'm running is too small? With the way the current one is mounted, there would be room to sandwich another in front, or there is room to up the aux fan from the current 12" to a 16" to increase airflow, but not both.

So the 5cyl sanden would be likely too small...what about the 7cyl thats currently in there?

leathermang · #19 09-05-2014, 03:48 PM

I really see no relationship to the size of the compressor and anything... since there are sensors for both high and low pressures...and temperatures in multiple places in the system...
If one were to want to increase the size of the ' already work inputted ' refrigerant..the side where it has gone through the condenser ... where for instance one could ' build up at higher speeds... then use at idle in traffic ( for a little while ) ... then I would suggest adding a receiver dryer to the one you have. There are valves which could be used to change out one at a time for moisture control ... if one needed that.... and it would be regulation MB stuff... these would be hooked up in parallel ... not IN LINE... that would mean one could be serviced without having to vacuum the entire system... I think the valves are called Roloc ... anyway.. they are mentioned in the archives..
and remember... as a test that 48 inch fan really meant nothing..You need one of those squirrel cage types immediately at your grill to impersonate traveling at speed.... and your blower needed to be on LOW with the windows OPEN... to insure that your compressor was on during the entire test... this is all per the FSM Mercedes AC manual.

leathermang · #20 09-05-2014, 03:51 PM

Quote:

Originally Posted by RavenTBK

.......What about adding a second 16x20 PF in series as the single one I'm running is too small? .....

No, then you are looking at impeding the flow of air ..not only to the second condenser.. But TO YOUR RADIATOR......
Do not want to trade one problem for another...

If you are convinced you have too small a condenser... just buy the biggest one you can properly get into the space provided..
AND add a High Efficiency FAN...... they are available....

RavenTBK · #21 09-05-2014, 04:22 PM

I'm not convinced of anything yet. I'm just trying to get better ideas on how to resolve the no cooling at speed issue. The thoughts that are being floated as answers really are doing nothing more than muddying the water in my mind. vstech says the condenser is too small, so the only alternative is a second one as the 16x20 fills the space available in LxW, but there is room in the depth department. vstech also says that a large compressor is a problem, but suggests that the 5cyl might be too small. I've got the 7cyl, so I fail to understand that problem.

I did use the squirrel cage fan in my more-recent previous post (#11) in this thread.

Its just really odd how this whole thing is working. None of it makes any sense, nor can I find any other sources of information that have experienced it either. The problem is always reversed...ala no cooling at idle, but good at speed.

leathermang · #22 09-05-2014, 11:01 PM

Quote:

Originally Posted by RavenTBK

..... vstech also says that a large compressor is a problem, but suggests that the 5cyl might be too small. I've got the 7cyl, so I fail to understand that problem.......

The only time a large cooling unit.... like installed in a house situation... is too large.... the problem does not become cooling... but HUMIDITY... because it cools so fast that it does not have a chance to drop the moisture from the air... thus it cools to the set temperature of the ' pilot operated' switch as MB calls it.... the setting the person sets the cooling temperature to... but you have a humidity level which is uncomfortable...

The Sanden design is so much better than the R4 it replaced that it is not too big with regards to the engine being able to run it... and the sensors and switches in the system make the decisions as to the temperature.... determined by the amount of liquid refrigerant the TxValve lets into the evaporator..... as long as there is compressed fluid refrigerant from somewhere above the bottom of the condensor.... to the Txvalve... then the compressor size is ok.

I still say that doubling up the condensers in front of the radiator is not a viable idea.
I would try a high efficiency fan next....

ROLLGUY · #23 09-05-2014, 11:38 PM

Quote:

Originally Posted by leathermang

I still say that doubling up the condensers in front of the radiator is not a viable idea.
I would try a high efficiency fan next....

I agree. The tests I have done on my 300D with a 7 cyl and stock condenser suggest that the lowest vent temps are had when the air flow across the condenser is greatest. IMO a large condenser fan (2nd gen 126?) would give the best cooling.....Rich

leathermang · #24 09-06-2014, 08:05 AM

Quote:

Originally Posted by RavenTBK

....... The thoughts that are being floated as answers really are doing nothing more than muddying the water in my mind. .......

nor can I find any other sources of information that have experienced it either.......

We are trying to suggest things based on your description of the situation there.. we can not " Lay Hands " on the car.... this is all blind speculation trying to help you figure out the problem.

" floated as answers ".... interesting.... but you admit NO OTHER SOURCES are available ... You are free to do your own research from the ground up... find a copy of a community college text which offers HVAC courses... I have one of those... get a copy of the Mercedes AC shop manual and read it... I have one of those.... go to ACKITS dot com, Aircondition dot com and learn about the basics of automotive ac....and ask on their forums for help... I spent a couple of years reading everything I could find on automotive AC.....

One other suggestion...... just to really muddy the water...... you have been working on the firewall forward...
but the evaporator is half the system....
and we have great threads in the archives which show JUST HOW CLOGGED the fins on an evaporator can get....and how to clean them safely...

Why don't you retry your test... blower on LOW... windows OPEN.... squirrel cage touching the grill basically... and relate the numbers...Are you using 134a gauges ?

funola · #25 09-06-2014, 09:29 AM

Quote:

Originally Posted by RavenTBK

.....

Its just really odd how this whole thing is working. None of it makes any sense, nor can I find any other sources of information that have experienced it either. The problem is always reversed...ala no cooling at idle, but good at speed.

If the belt is loose, it may produce the symptoms you are having. Grab the belt by hand and try to forcefully turn the compressor pulley. If you can get the belt to slip relative to the pulley (i.e. belt moves, pulley remains stationary), the belt is not tight enough.