whistling noise??

[noacguy]

Hi,
there is a high pitch whistling sound coming from somewhere in the ducts when our AC is on. this happens after the unit has been runnning for a couple hours.. there is cold air comming from the vents. we've just turned the AC on yesterday..its getting too hot!

does anyone know what might be causing this whistling noise and possible solutions? Thanks!

[mattison]

Check all your vents and your filter. Sometimes your return vents just need a little tweeking to let the air pass differently.

[noacguy]

thanks for the suggestion. i went through the house checking all the vents and replacing the filter. the noise is still there after a couple hours.

when i took a look at the evaporator coil, there is thick frost all over it..and on the lines leaving the evaporator. is this a bad sign?

after some more looking on this site, i cut the power to the compressor and cleaned the condenser coil outside w/ the hose. now its been a couple hours since i've turned the AC back on...there is some frosting on the evaporator coil, but nowhere near as much as before, yet..

is this frosting normal operation? or is this pointing to a leak?
thanks again.

[Grady]

The whistling could be an indication of lack of air flow which will cause the evap coil to frost. The frosting could also be an indication of low refrigerant. As a quick & dirty test, here's something to try. After the system has been off long enough for the coil to completely thaw, set the thermostat for "fan on" & open the door to the air handler (or furnace). If you have to pull hard to get it off & air rushes in thru the door opening, you probably have a return air problem.