The Bissell Powerfresh Steam Mop 1940 and 1940a are the same.
The difference between Bissell 19404 and 1940/1940a are as follows.
Bissell 1940a vs 19404
The Bissell 19404 PowerFresh Pet Steam Mop comes in White with Purple whereas the 1940/1940a is in White with Blue.
Included Fragrance Disc Type
The Bissell 1940/1940a comes with Spring Breeze Fragrance discs whereas the Bissell 19404 comes with Odor Eliminating Fragrance Discs for neutralizing odors.
List Price at Bissell.com
The 1940 is priced at $89.99 on Bissell.com whereas the 19404 is priced at $89.00.
Other than the above things, they are identical.
They weigh 6 pounds; feature swivel head; flip-down easy scrubber; built-in heater; 23 foot power cord; 12.5 cleaning width; removable water tank with 15 oz tank capacity; have 3 steam settings – low, medium and high; come with 2 microfiber mop pads; have no filter.
And carry a 2 year limited warranty.
Since there are no mechanical difference between these Bissell Powerfresh Steam Mop models, just purchase the one with the lower price, or buy the one that comes in the color you like.
If you want to learn more details before making a purchase, here are 2 links to download the manuals:
Bissell 1940 series manual:
Bissell 19404 manual: