Cleaning the Evaporator may seriously improve the airflow through the evaporator, making the AC performance a lot better. After time dust and debris clogs the evaporator on the engine bay side.

It is not easy to access the evaporator. It helps removing the hood but this is not required. it also helps having small hands and some patience. Consider taking the HVAC resistor pack out to have better access to the far end.

You will have two options:

1. clean up in dry state, which will work for just dust and some debris

2. clean up using soap, foam, and water to rinse

Choosing Option 1: get a vacuum cleaner extension so that you can access the evaporator. Since the evaporator fins are fragile and you don't want to damage anything in there,  make an extension from the foam that is also used to insulate heating pipes. That makes it soft and easy to bend. Or use soft plastic tubing. You can consider using a small brush or a tooth brush to release the dust from the fins.

Choosing Option 2: get a vacuum cleaner that can take in water, and make an extension so that you can access the evaporator. Since the evaporator fins are fragile and you don't want to damage anything in there,  make an extension from the foam that is also used to insulate heating pipes. That makes it soft and easy to bend. Or use soft plastic tubing. Foam the clogged area, let is soak for a while and use the vacuum suction to clean it out. repeat several times. If you rinse with water, make 100% sure that the drain is open. Otherwise you poor water over the CEB and ECU's. You can consider using a small brush or a tooth brush to release the dust from the fins.

Here are some pictures:

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As I am absorbing more and more insight on how AC systems work. I learned that the evaporator’s efficiency can be hindered by dirt and debris. Accessing the evaporator is pretty easy if you about the size of a mouse, otherwise it’s not an easy task. You can get a view of one side of it from under the cowl once you have removed the cowl, wipers, cowl trim, hood, and blower fan. And then, you still can only reach it with a long handle brush.

Here you can see the blower motor left and the evaporator housing right. You get the idea. Not much room to work with.

The 928 didn’t use a pollen filter until 1994 so all the dust and debris gets blown onto the evaporator. Take a look at mine before cleaning.

Here is some of the debris I removed

I was able to get it a lot cleaner just by using a vacuum and compressed air, but there was still stubborn stuck on grit.

At this point my options were to stop, or get in there for some more aggressive cleaning with bottle brushes and/or some foaming cleaner. I decided I would continue to work with sprays or foams because I didn’t want that gunk potentially clogging the drain. I purchased some bottle brushes and got in there to agitate the debris and suck it out with the vacuum as it turned back to dust. It got a lot better, not perfect but clean enough that I am not going to use foam. I should also point out I removed the temp probe and the resistor pack before getting in there with the brush. It made it easier

On re-assembly I decided to improvise a debris filter to stop the larger bits from getting into the evaporator. I cut up a used furnace filter and while this won’t stop dust, it will catch the large bits and should not limit airflow.

Benno.

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