740 AC Evap Coil Cleaning

How dirty do the filter-less 740 AC evaporation coils get after 30+ years of use?

While my AC is adequate for Florida summer in a near-black car, I can't help but wonder how the evap. coil looks after this much time and constant use, and how much it may affect AC performance.

That being said, is there a method or product to use to clean the evap. coil and is it worthwhile?

Also, as long as I am on the topic of the AC, whenever I forget my AC on recirculation (big snowflake), the next morning the first bit of air that blows out downright smells like vinegar. This doesn't happen when it is set on fresh air. Anyone know the reason + a possible solution?

Thanks in advance!

The evap coil probably needs a bit of refreshing cleaning. Wurth used to sell a product that was an aerosol with a straw on it so you could blast into the chamber from any hole you can find big enough. Or drill an access hole and cover it with some stainless metal tape afterward. You can also get evap coil cleaner from an HVAC supplier.

I use foaming cleaner on my central AC in my home every now and then, but I just don't know how I would get that stuff to the evaporator coil on a 740. As for the recirc. problem, where do 740s pull air when the AC is set on the big snowflake?

I wonder if spraying Lysol or some sort of disinfectant there would help with the odor issue.. Maybe something like THIS would do a good job?

The last thing I'd like to do is get chemical odors blasted into my face while driving. I'll check to see what the local auto parts store has regarding deodorizing without just "masking" smells.

The wurth stuff I mentioned is for deodorizing the a/c. You use the included straw to spray it in the dash vents.

At work we used 'coil trate' which is formulated to clean off the coils aggressively without harming them. I'm sorry but I have no idea how you are going to access the evaporator with the system still intact and the interior not stripped...

I suppose you could try taking out the fan (bottom right behind the glove box), going up through the hole and turning left to where the core is (big rectangular box in the middle). Not sure how wide the "pinch point" is where the duct narrows, but you should be able to either spray something through there, or perhaps snake a small vacuum cleaner hose in there to suck out all the decomposing leaves and dead bugs that are piled up against the core.


From my heater core adventure several years ago:




Parts catalog pic:

daniels740 said:

How dirty do the filter-less 740 AC evaporation coils get after 30+ years of use?

Click to expand...

But there is a filter ..... it's 30a in the parts pic, part number 1307522.
Yes, *after* the core.

Drill a hole and then cover the hole with the stainless steel tape they sell at hvac suppliers.

Had the chance to check what the local auto parts store has for deodorizing today, and they only have those foggers and the like, not anything like the Wurth spray mentioned which is specifically for the HVAC system and vents.

Really, I've just gotten into the habit of leaving it on fresh air rather than recirc. and there's no smell whatsoever. If I'm really bothered, I'll try Lysol or track down a can of that Wurth stuff.
As for cleaning the coils, I guess it's not worth the time considering that the AC works fine as is. I was just curious to know if there was an easy method.

Thanks to all who replied!