What is the recommendation for cleaning electronic air filters? I am being advised by one dealer that the electronic air filter must be vacuumed, not washed because they are subject to corrosion and may cause malfunction in the unit. Another dealer who has serviced my unit since installation states that backwashing the electronic air filter does not harm the units nor does it cause a malfunction. I do not have an owners manual but the model numbers for each unit is as follows: K1T 15701 and TFD215ALAH000BB and serial number for each is, respectively: 11612TE1E and 8121LL97V. Please advise.