Well she left all the windows closed so the added moisture from the rain with no air flow caused mold/mildew to cover her stuff for the same reasons attics have soffits. 

You just cant fill the void between the ceiling and the roof with insulation , there has to be airflow or venting .

Her lease states that she should be changing the filters monthly and, in a subsequent section, that she would be liable to reimburse us promptly for damages... and service required by violating her lease rules.I feel we are within our rights to request a $75 reimbursement for the service call and have this drafted:Dear [tenant's name]:Per your lease agreement, we are enclosing a bill for $75.00 and a copy of the HVAC technician’s findings and the diagnostic call receipt for services required for a “severely clogged air filter blocking the air flow causing the AC system to freeze up”.Per your lease agreement, section 19B, you must replace air-conditioning filters monthly, which would have prevented the clogged air filter issue.

The more frost and ice develop the air flow is restricted and the coil becomes a block of ice.

Household furniture must be positioned and/or elevated to allow adequate air flow underneath and between furnishings and adjacent walls.

Opening windows and have large fan would help with air flow.

I would use the resources like yellowpages, google reviews, ask at a real estate investor meeting or maybe sign up for Angie's list and find the best HVAC company and installer who, stands behind the product, is willing to educate you on the right equipment and provide you a fair quote.Your investment strategy, and what the standard is in your area will dictate the price.I would look for the Highest seer, with a good warranty 10 compressor, 10 year parts, look for one with quiet technology (compressor sound blanket, motor mounts, Air handler blower motor, air flow designed for quietness) and ease of service for the air filter, air handler coil cleaning, overflow float switch, and access or instruction on drip pan tablets/liquid and drain line cleaning.What I look for in a HVAC installer is someone who is proficient and not on the phone or looking through the manual a lot.  

You can cut vents into the walls and the natural airflow should be sufficient to dry it out.

If it is not changed it will restrict the air flow and cause the furnace to work harder which will eventually require additional service=$$$.

It could be a lack of proper air flow around the coils, the condensate not draining away properly or draining too slow, the refrigerant could be too low or leaking, the air filter could be clogged, a damaged or broken fan, etc.