A friend of mine was helping me replace the expansion valve on my '90 300SL. I don't see how, but he stripped-out one of the bolts securing the valve. We ended up cutting it off with a saw, and as a result there were many small filings in that area of the engine compartment.

I think some filings may have made their way to the evaporator and have considered having it flushed. But when I spoke to a service advisor at the dealership about getting this done, I was told it was not necessary. He explained that any filings would simply pass through the side of the expansion valve that performs no metering and would get caught by the receiver/dryer.

This seems plausible to me. But before I install the new expansion valve, I wanted to ask the experts here what they think: is it okay not to flush the evaporator?

The a/c is one place I don't like to take shortcuts or do anything less than a perfect job. How much trouble would it be for you to flush the evaporator? For example, I have compressed air at home, so for me it's no big deal.

The service advisor may be right, but wouldn't you want to make sure before you put everything back together, and went to the trouble of evacuating and recharging the system?

BTW, are you doing a conversion at the same time? If so, you should probably flush regardless of the filings.

__________________
95 E320 Cabriolet, 159K

Since I don't have access to a compressor, I would have to pay someone to do the flushing. A recent post by Steve Brotherton described the meticulous steps that he takes in flushing an evaporator, and I decided I must take care in choosing a shop to do the work. It seems an incompetent flush could do more harm than good. And I just don't know who I could trust here in Las Vegas to do good work. This is why if it is not deemed improper, I would prefer to skip the flush.

I should mention that I am fixing the A/C on this car only because I intend to sell it. Still, I want to do right by the future owner and make a proper repair. I would rather spend $500 or whatever and flush than spend nothing and no flush if this prevents the next guy from trouble at some point down the road...

And regarding conversion, I'm going to stick with R-12. Steve Brotherton and Larry Bible have convinced me it's best to do so.

Guess the service advisor forgot to tell you that the metal filings will have to pass through the compressor first before reaching the R/D. And that your ND compressor is not equipped with a low side filter.

If the filings are in the evaporator's high pressure supply side, then they will pass through the evaporator, exit on the low pressure discharge side, pass through the expansion valve and then straight to the compressor. Some particles may stick in the rubber lumen of the suction manifold hose, only to be released at a latter date.

If the filings are in the evaporator's low side discharge pipe, then its through the expansion valve and straight to the compressor.

Odds are the filings will never make it to the R/D. But they will trash your compressor.

Flush. And don't forget to correct your refrigerant oil level afterwards - include both oil that is removed from the evaporator by the flush and any that may have been lost during the period of your refrigerant leak. And if the R/D has never been replaced, consider doing so. The car is 12 years old; a new R/D is warranted.

I see now where it would be a huge mistake to suppose the receiver/dryer would catch the debris. Maybe the service advisor imagined the compressor draws refrigerant from the r/d instead of the evaporator?

As an additional precaution against debris reaching the compressor, I plan to install an inline filter at the suction port. A link to the website is here: http://www.airsept.com/ac_inline.html

Were it mine, I would do everything possible to flush the evaporator as best it could be flushed, THEN I would use a suction side filter. There are screens that you can get and other aftermarket products.

Don't take a chance with this, the stakes are too high. I recommend that you post a message for Tom on the www.ackits.com to see if he can recommend a suction side filter of some sort.

BTW the service advisor that told you that these filings would be trapped by the filter drier needs to take up another line of work. He obviously doesn't know what he's doing in his current position.

My $0.02,

Larry B, whilst on the subject of the receiver/drier, it has been mentioned in a UK forum that it is advisable to renew this item every 5 years (Cost circa 105 dollars + fitting)
What are your thoughts on that please?

Tigerfox

I have heard this a few times over the years.

My thoughts are this: Not only would this procedure provide the chance of creating a leak at the filter drier fittings, it also provides a chance to possibly not get the system fully evacuated leaving moisture in the system. ANY moisture left in the system will combine with refrigerant to create an acid that will eat a hole in the system, most likely the evaporator, from the inside out.

My conclusion is; if the system has held refrigerant for five years without an appreciable leak, it has had no possibility of moisture contamination, by the operation of changing the filter drier, you are introducing such a possibility. My mode of operation is to ALWAYS change the filter drier and thoroughly evacuate whenever the system is opened, but don't open the system unless it must be opened to make a repair.

In my way of thinking, this is one area that should be approached with the old saying; "if it ain't broke, don't fix it."

This is MY opinion.

Best of luck,

Tigerfox, you may have heard a misinterpretation of policy where the drier is changed when the system is breeched and has more than 5 years on it. Breeched - meaning outside air has had a chance to enter the system... not a leaky system that has maintained positive pressure at all points.

Some poeple don't change the drier if the system has less than 5 years service and it's open only for a short while during repair. This isn't a hard and fast rule, and some people may frown on this practise, saying you MUST change the drier anytime the system is breeched.

NEVER change a drier on a properly working a/c system simply for maintenance. It is a closed and sealed system.

__________________
95 E320 Cabriolet, 159K

Larry B. Kestas.

Thank you both, excellent logic.Will adopt your advice.

Tigerfox