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Flushing Mercedes-Benz W210 evaporator

Matt L on Thu August 07, 2008 10:05 PM User is offline

Like many TXV systems, the evaporator inlet and outlet are accessible from the engine compartment, once you remove enough of the bits that are in the way. It's still not extremely accessible; you have to fit your hands into a fairly small space to remove the screws holding the TXV onto the evaporator tubes.

In addition to the tight space, the evaporator tubes are quite flexible at the firewall. This made it seem very dicey to hold the flush gun against the tube. It tried to wobble all around with the flushing, and of course caused me to squirt some of the fluid out and all over (myself, the car, etc).

I attached a 6" or so length of an appropriate size of vinyl tubing to the evaporator inlet with a small hose clamp. Not so tight so as to deform the aluminum tube, but tight enough to hold it on. Then I screwed a pipe nipple into the flush gun and clamped the other end of the vinyl tube to this, and hit it with the HECAT magic. I was able to sustain quite a large flow through the system this way, without worrying about placement of the dispensing handle and without losing any solvent before it got into the evaporator.

There was then very little restriction at the connection. The instructions say to use the "large" tip if possible, but it seems that sometimes no tip may be best. It worked like a charm. Is there a chance that no restriction at the tip can cause the wrong sort of action? It seemed to be pulsating quite violently.

HECAT on Fri August 08, 2008 6:12 AM User is offline

Yes, this is a design issue with many vehicle models today.

The evap tubes are a manifold that the TXV bolts to, and it is all low on the firewall behind a closely mounted engine; making it difficult to attach the flushing tool. This is a challenge regardless of whether you are using the Pulsator Flush Gun (PFG) rubber tip or the pro flushers universal adapter kits clamping connections. There are some manifold style flushing adapter kits available that would bolt in place of the TXV, but such kits can be very expensive.

HECAT has always recommended in such tight confines, to use a gutted (clearance drilled) TXV and the hose assemblies to obtain a clear flow path and a flushing connection point. Sometimes it is possible to attach the hose assembly directly to the evap after the TXV has been removed. It is also recommended to save many if not all removed TXV bodies and hose assemblies as future flushing fixtures. AMA's shop has a shopping cart full just for this reason.

Such issues do and will require some diligence and creativity on the part of the technician. Good job Matt.

The warning about the PFG small tip is in regards to restricting the flow and how this begins to reduce the effectiveness of the process. Allowing the maximum or full flow at any time we can will produce the most effective flushing flow, Pulsating action, and desired results. Just be sure to use your same connection to apply the "Dry Air Purge" to remove the solvent and always perform the verification "pop" test before beginning to reassemble.


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FLUSHING TECHNICAL PAPER vs2.pdf 

Matt L on Fri August 08, 2008 12:27 PM User is offline

I didn't consider gutting the TXV and reinstalling it. That would have made the job somewhat easier, and I did have a new TXV to install. Next time, and hopefully on a different car.

I did use the same setup for the purging and "pop" test.

Thanks for the response.

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