I have been cleaning the blowers very often the past year, literally 6-8 weeks once for each FCU. 
I find that the aircon cleaning foam (basically a surfactant to loosen the dirt etc) is optional if it's done regularly.  Just use the Panasonic oral irrigator to blast the dirt.
90 PSI of water (very low volume of water though) is extremely powerful. For comparison's sake, your HDB is approx. 35 PSI.
Just blast at the aircon blower fan and also the metal fins.  I use 2 pcs of rags and 2 big plastic containers (Wash clothes one) to contain the dirty water.
My fins and blower fan is as good as new, spick and span.  Max efficiency. Use a flashlight to shine on them.
Won't spoil....