No Cold Air
No, cold air can happen at anytime. Typically a cost effective repair will get you the desired temperature in your house. Majority of the repairs can be prevented by having a Seasonal Tuneup performed in the spring and fall. The home has to do there part in maintaining there unit. One way that this can be done; is to change your quality air filter on a regular basis. A trained professional can help you determine that desired cycle.
Strange Smells
Strange smells come from your hvac system is typically not a desired thing. The most common problem for is that the ducting has not been cleaned out and biological items are in your ducting. Some smells can be removed via a duct cleaning, indoor air quality machine, or be found via a seasonal tuneup.
Weak Output
This can stem from an hvac system not being cleaned annually or from an air filter not being changed on a regular basis. The most severe case would be from the hvac system not being correctly installed. A seasonal tuneup could help to fix the first two problems. The second could be a bit more complicated to fix.
Moisture
Moisture in the wrong location could be a problem. This could lead to a biological problem in your hvac system. When moisture has allowed biologicals to grow a side affect could be insomnia, nasal drip and or a strong odor coming from your hvac system.
Unusually high energy bill
Having a high energy bill is almost expected during a hot summer. There are ways to help prevent this. A properly sized system will help to insure that you are generating the correct amount of heating or cooling. An improperly maintained system could be a factor in a high energy bill.