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Old 06-29-2019, 10:08 AM
Bengoshi2000's Avatar
1991 300D 2.5 Turbo
 
Join Date: Jan 2011
Location: NC, USA
Posts: 267
AC Evaporator Cleaning - W124

I'll start off by saying that my long range plan (i.e. next spring) I'm going to pull the dash, replace the evap core and txv... in short, go through the entire system piece by piece; seal by seal, and get it back to 100% functionality.

But in the meantime:

1) Has anyone tried to clean the evap core from the backside (i.e. by removing the blower fan and trying to vacuum the crap out)? The po parked this car under a tree for several years and I can only imagine the mung that has settled in there.

2) Has anyone found a way to retrofit some filters in there to prevent the free flow of crap into the core?


Background:

I don't think I'm having serious cooling issues (until ambient temps hit 90*F+ and the humidity is above 75-80%... at that point I'm getting 45-50*F at the center vent with city driving). On a longer trip the center vent comes down to 40*F after about 10 minutes of driving.

If ambient temps are in the low 80's, I can get 38*F at the center vent (holding the rpm at 2,000). It will idle at 42*F.

I routinely get 38*F at the center vent in the morning on the way to work (about 75*F ambient).

I feel like the ac system is performing decently, I'm just looking to eliminate some easy variables (like a clogged/dirty evap core) that might improve things somewhat.

EDIT: For these testing conditions fan was on MAX, temp wheel turned all the way down to the dot.


For the record:

1) still running r-12 and I know I have a small leak somewhere (odds are in the evap core).
2) no, I don't have any r-12 gauges (and yes, I know I need those to properly diagnose problems).
3) the recirc button in the car is just for show at this point. I'm sure that it's not working (probably the vac pod).
4) I've sorted out all vacuum issues to the vacuum manifold relays behind the glove box. I also pulled the relay, split it open, and re-flowed all of the solder joints on the pcb (3 of them were really bad). Amazing how much that improved things.

Any further "low hanging fruit" ideas or suggestions?

Peace,
Norm
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Last edited by Bengoshi2000; 06-29-2019 at 12:01 PM.
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Old 06-29-2019, 11:49 AM
Diseasel300's Avatar
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Location: Texas Hill Country
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A dirty evap will reduce airflow and increase frost accumulation on the coil face. If you're not having airflow problems or excessive cycling of the compressor, it's unlikely to be a source of problems. It could stand to be cleaned at this point, but it probably won't make much difference in performance.

Your recirc issues should be addressed pronto. Even a small amount of outside air leakage on a hot, humid day will make the system performance suffer. You haven't mentioned if your vent temps are with the fan on max speed, or low speed. If the system is properly charged and working correctly, once the cabin pulls down it should be able to maintain a vent temp in the mid-low 40s with the fan on max speed when moving, drifting up to ~50 when idling for a period of time.

Not sure on the 124, but the 126 (which uses the same HVAC system) has an evaporator temp sensor that trips the compressor clutch off between 36-41˚. Airflow is always slightly warmer than the coil, I've never seen a vent temp below 42˚ as a result.

My SD had a bad evap temp sensor and would let the coil freeze. You could hang meat in that car....until it was a humid day. Then the coil would freeze. The main symptom was that the fan seemed to be on low and the air wasn't that cold coming out the vents. Run on EC for a while, and it would melt the ice and be back in business. Replacing the sensor ended that behavior.
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Old 06-29-2019, 12:07 PM
Bengoshi2000's Avatar
1991 300D 2.5 Turbo
 
Join Date: Jan 2011
Location: NC, USA
Posts: 267
For all my "tests" above the fan was on high, thermometer was in the center vent, and the temp wheel was turned all the way down to the "dot" (still unclear on what the "dot" means). OP edited.


Quote:
Originally Posted by Diseasel300 View Post
If the system is properly charged and working correctly, once the cabin pulls down it should be able to maintain a vent temp in the mid-low 40s with the fan on max speed when moving, drifting up to ~50 when idling for a period of time.
This very nearly describes how the system behaves. So perhaps I'm in the ballpark of "properly working"? (and should worry about something else?)
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Old 06-29-2019, 12:35 PM
Diseasel300's Avatar
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If you can easily access the evap core, use some of the foaming cleaner from Lowe's or Home Depot, then rinse with water from a pump-up sprayer. It'll help the overall capacity of the system, but won't affect vent temps much. If it's a serious PITA to get to, it sounds like it's working well enough to leave it alone until you get in there to do more serious cleaning.
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  #5  
Old 06-29-2019, 06:21 PM
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I really spent time cleaning my evap core out from the outside with the fan removed. Combination of shop vac and compressed air and I think I did ok. Mine wasn't too bad in the first place. I would make sure your sampler fan is operating correctly and not disconnected - it is in the cavity behind the glove box and pulls air through a sensor in the panel next to the sun roof switch and it tells the climate control unit what the cabin temp is (not a technical description of its function). In two 124s fixing the sampler fan eased some issues with the a/c.
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  #6  
Old 07-02-2019, 11:08 AM
WTB: 94/95 E320 Wagon
 
Join Date: Oct 2007
Location: Charleston SC
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Quote:
Originally Posted by Bengoshi2000 View Post
I'll start off by saying that my long range plan (i.e. next spring) I'm going to pull the dash, replace the evap core and txv... in short, go through the entire system piece by piece; seal by seal, and get it back to 100% functionality.
Just did this (evapectomy) on my '87 300TD. Had a small leak from the evap that was getting worse, tried Clip Light leak sealer but that didn't work. Took about six hours to remove the heater box, a couple hours to refresh that with new evaporator and newish vacuum pods, and then another six or seven hours to get it all back together. The condensate drains from the bottom of the heater box were the biggest time sink, not included in the hours above, requiring multiple trips to / from local hardware stores until I found a suitable replacement for the foam hoses that disintegrate when you touch them. Eastman #0023546 Dishwasher / Disposer drain outlet adapter, reduces from 7/8 ID to 5/8, fits with no modifications and includes hose clamps.

Sadly after just one day, the shaft seal on the front of the compressor blew out, so now I get to pull and reseal the compressor.

Quote:
Originally Posted by Bengoshi2000 View Post
But in the meantime:

1) Has anyone tried to clean the evap core from the backside (i.e. by removing the blower fan and trying to vacuum the crap out)? The po parked this car under a tree for several years and I can only imagine the mung that has settled in there.
Yes, not much there. My driveway is nicely shaded by trees, I've parked there for over a decade, but I do make an effort to remove the debris that falls into the cowling area every couple weeks or so. The factory design is actually pretty good at keeping junk out. You may not find much there.



When I had access to the underside of the heater box, on the "dirty" side (engine compartment), there was surprisingly little accumulated dirt and leaves. I'm referring to the black hole around the blower fan, outside the heater box, not inside where the fan and evaporator core live.


When I pulled the evap from the heater box, there was some junk collected at the top edge, but that was impossible to get at without removing the heater box and pulling the evaporator.

Quote:
Originally Posted by Bengoshi2000 View Post
2) Has anyone found a way to retrofit some filters in there to prevent the free flow of crap into the core?
The later years of the 124 include a filter, you could snag those parts from a junkyard and retrofit into your car.


Given the vent temps you are reporting, I think your system may have a bad temp sensor and your evap is icing up? I don't think you've got an issue with a plugged up evaporator.
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'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
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