grinding noise on startup I have 2 ac units that grind on startup (one worse than the other) It only lasts for a second then stops. I had the hvac guy here to check it out and he's stumped. amp test proved normal. Things I can thing of are bent fins, bad blower motor (or low/no oil) and low amount of refigerant although the air is cool as it blows into the home. Re: grinding noise on startup You can rule out low oil/no oil and low freon would not be your problem. You stated that both units were making similar noises leading me to believe that both units were serviced and or installed by the same person and could have an overcharge with some liquid lying in the crankcase on startup and this would make a noise. A bent or broken internal compressor mounting spring could also make a noise but the probability of both compressors having that same problem is un-likely. If it is not the fan or the freon charge but is an internal noise from the compressor there is no exact way to determine this on a hermetically sealed unit and you will probally never know the reason until failure.

Bruce where would you put a check valve in what freon line and what would be its purpose. I personally have never read any MFG instulation instructions that restricted verticle height they will require the size of the liquid and suctions lines to be increased for length but not necessarly for height. build roof over ac unitHave installed tons of units on two story homes with no problemsair handling unit system I think you are on to something there.does a window ac unit have to be tilted It's impossible to hear the grinding over this board so this is a WAG not a SWAG. Seeing that both units are doing it, it should not be a defect. It is unlikely that both would have the same defect at the same time. (ie. fans, motors rubbing, bearings, blower wheels)

Also, scroll compressors have a tendency of being loud (starting, running and especially when stopping as they run backwards during pressure equalization). Now, on to you guys. Refrigerant migration could be a factor. Evap up, cond down: If the refrigerant metering device is other than a TXV it may flood the compressor as it allows the liquid refrigerant to pass through the metering device rapidly until equalized. You guys hear this surging of refrigerant for a while after the unit shuts down from up in the house at the air handler?. A TXV will "slam shut" when the compressor suction stops (most residential valves still have a small equalizing orifice inside the valve). Creating a "Pump down" or just a "shut down" configuration by installing a solenoid valve in the liquid line will correct this. However, a hard start kit may be needed if the compressor doesn't have a start capacitor as the compressor must start against the head pressure of the refrigerant caused by the elevated AHU.

Excessive refrigerant charge (due to system design): The amount of refrigerant in a system must be kept to a minimum. Arbitrarily installing over sized lines may cause this. These flooding conditions are more prone in over sized refrigerant circuits. No crankcase heater in a scroll compressor (or reciprocal compressor where slugging is occurring): Mfgs think the scroll is tuff and doesn't need an accumulator, start capacitor or crank heater. Refrigerant has an infinity for oil and during shut down it will migrate to the crankcase of the compressor. At start up the refrigerant (and the oil) are sucked up through the compressor. It makes one hell of a noise! Look for a compressor in a cooler location than the AHU (like the AHU in a 200 degree attic space). Installing an accumulator in an A/C that doesn't have one will help with a flooding situation. The HVAC Tech should be able to identify this stuff. Now you are making sense to me with the exception that I have always installed a LSV if required just prior to the entry of the A-coil box.

Identifying Air Conditioner Noises and Smells Sometimes unpleasant smells and noises coming from an HVAC unit can indicate a problem with the system that could require maintenance orIf you’re experiencing air conditioner noise or if your air conditioner smells a bit funny, there may an issue inside your system. Components that could experience these problems include: • Compressor – While compressors are noisy by nature, if your compressor is making loud or unusual noises, it may be worn out. • Drive Shaft or Fan Blower Motor – If the drive motor is making loud noises, it may need some lubrication. All motors need to be lubricated at all time, otherwise it will wear out. Loud noises may be either• Fan Blade – If one of the fan blades break off, it can start rubbing against the house and cause unwanted noise. If the air from your system smells musty, it may be due to mold and/or mildew buildup in your duct system.

One way to get rid of this is to change the filter and clean the drip pan in your HVAC system. Clean using bleach or white vinegar to make sure the area is no longer hospitable to mold growth. Common furnace noises and their causes There are several furnace noises listed below, some of which could indicate a problem with the unit. If you’re concerned about a furnace noise contact your local American Standard dealer to schedule an HVAC check-up: • Screech – This could be a problem with your motor or fan• Chirp – Chirping sounds are fairly common with furnaces and usually the natural noise of the mechanisms. Rattling noises typically happen when the system is cooling down and it not usually cause for alarm. • Boom – When the weather outside warms up or cools down, the ductwork in your house expands andIf this happens and your furnace smells like it’s burning, you might have a dirty burner in your furnace or a defective gas

• Ping – This sound can also be caused by contracting • Hum – When the furnace burner lights, it may cause a humming• Whine – Whining or odd vibrating noise may indicate a problem with your furnace. • Crackle – Crackling noises may be the metal parts cooling down after the furnace shuts off. Clunk – Clunking or bumping sounds often means you have a cracked belt. The best way to determine whether your furnace is making an odd sound is to learn what it sounds like during normal operation, and note any changes in the type or volume of sound as the unit ages. you notice a significant change, call your local American Standard dealer to schedule an inspection. Professional help for unwanted HVAC noises and smells If you’re experiencing unwanted noises or smells from either your hvac system, call a professional. While some noises are normal, others could indicate that something is wrong with your system. Standard Customer Care dealer