Home AC checkup - how to avoid getting ripped off?

[soupcxan]

I'm thinking of having an HVAC guy come out to check our home AC, it still cools but not as much as I think it should, and lately it's been making a kind of oscillating-humming noise (maybe uneven fan blades?). The checkup is cheap but I'm sure they are looking to sell you additional repair services, "oh yeah you need to get the optional rustproofing package". Other than trying to find a reputable shop, are there any tips for reapirs that AC repairmen might suggest that I should actually consider versus those that are [-]pure margin[/-] gratuitious?

 

[Meadbh]

Check the brand of your equipment, e.g. Lennox, Trane. Use a qualified dealer. Just had my A/C checkup last week. A new filter works wonders! Next, time to get the robotic duct cleaning done.

 

[REWahoo]

This looks reasonably comprehensive to me:

Q: What does an air conditioning check-up consist of?

A: It consists of the following steps:

1. Check for proper refrigerant (freon) levels. A low level indicates a leak, to be found and repaired before adding more freon.
2. Check all electrical components and controls.
3. Clean evaporator and condenser coils, as needed.
4. Oil motors as needed.
5. Calibrate thermostat.
6. Check Condenser.
7. Check filters.

Air Conditioner Maintenance - Tips for Homeowners

 

[calmloki]

http://www.epa.gov/iaq/pubs/airduct.htmlQUOTE=Meadbh;937952]Check the brand of your equipment, e.g. Lennox, Trane. Use a qualified dealer. Just had my A/C checkup last week. A new filter works wonders! Next, time to get the robotic duct cleaning done.[/QUOTE]

Threads in the last year regarding duct cleaning. TAl had it done and I didn't get the impression he was tickled.
http://www.epa.gov/iaq/pubs/airduct.html

Knowledge about air duct cleaning is in its early stages, so a blanket recommendation cannot be offered as to whether you should have your air ducts in your home cleaned. The U.S. Environmental Protection Agency (EPA) urges you to read this document in it entirety as it provides important information on the subject.
Duct cleaning has never been shown to actually prevent health problems. Neither do studies conclusively demonstrate that particle (e.g., dust) levels in homes increase because of dirty air ducts. This is because much of the dirt in air ducts adheres to duct surfaces and does not necessarily enter the living space. It is important to keep in mind that dirty air ducts are only one of many possible sources of particles that are present in homes. Pollutants that enter the home both from outdoors and indoor activities such as cooking, cleaning, smoking, or just moving around can cause greater exposure to contaminants than dirty air ducts. Moreover, there is no evidence that a light amount of household dust or other particulate mater in air ducts poses any risk to your health.