Crawl spaces usually have vents for air flow.

As long as the airflow matches the coil you should be just fine.

I learned that caulk and paint will fix any gap in a window.Speaking of unwanted airflow, my insulation education was top notch, just cover every window casing in its entirety with plastic sheeting.

Common sense indicates that 1. it's a fire hazard and 2. it's restricting the airflow and probably caused the overheating.I called the repair place and talked to the tech, he confirmed that the cardboard was there when he showed up, so at least the tenant can't claim he just happened to put it there yesterday.

Add a ventilation fan to the laundry area and/or forced air flow, to help keep the moisture down.6.

Read about them here: http://www.newair.com/articles/oil-filled-heaters/------HEATING, COOLING, AND VENTILATION SYSTEMS.Landlord agrees to maintain heating, cooling and ventilation systems on premises that are provided by Landlord.Tenant agrees to notify Landlord in a timely manner, and in writing, of any problems that arise with these systems.Tenant agrees to keep heating and cooling systems in good working order and to take safety precautions in accordance with their use, following manufacturer and fire department recommendations.a.Natural Gas furnace system:Tenant will not store items in the furnace closet, except for replacement filters.Tenant will allow Landlord to replace furnace filters when Landlord determines it necessary.Tenant agrees not to block air ducts (warm air output and cold air return) and to pay for any damage to the heating system caused by failure to do so.b.Electric baseboard and wall fan heaters:Tenant agrees not to block the heaters, to keep all flammable materials at least one foot from the heating device and to maintain ample air flow around heater.

If you want to take the DIY method for it, bring it home, stack it with little boards in between it for airflow, tarp it and set off 3-4 bug bombs under the tarp.  

Freezing up usually points to a couple issues: 1) dirty filter on the indoor or outdoor unit so it doesn't get the airflow it needs to transfer the heat or 2) low refrigerant.

If the unit has good air flow, such as you would find with a forced air HVAC system, it will lessen the chance of moisture build up.If the tenant had blocked the sliding glass door and surrounding area with excessive furniture, boxes, or clutter, then that could lead to moisture getting trapped.

I had jacked up the insulation to about 24" (90% plus of HEAT GAIN is through the roof), I had SOLAR SCREENS on all south and west facing windows, all of my windows and doors were well caulked to prevent air leaks, all of my units had electronic/automatic set-back thermostats, whenever I replaced a roof I went with a ridge vent to improve air flow through the attic.