4,303 posts, read 9,542,717 times 8,923 posts, read 33,173,370 times Originally Posted by chilaili I bet you bought one of those "efficient" pleated filters? 2 posts, read 39,263 times I bought a home back in August and the previous owner had a new 3-ton HVAC system installed. Basically right now the HVAC is located in the upstairs hallway, and the way the duct is set up is there is a central return vent right underneath it (12x24) that pulls air directly into it and another return duct in the master bedroom (16x24). I have noticed that the main return vent under the unit makes a loud whistling sound when the unit is running. If I open the vent I can see that the air filter is bowing inward because the unit is sucking air in so hard it causes a lot of pressure. This does not seem normal. I am wondering if there is not sufficient return. It could just be that there is a lot more air being pulled in at the main vent because that is the closest opening (path of least resistance).

The upstairs bedrooms often get very hot during the summertime and especially when the doors are closed, since the gap under the door is not very big and the inspector said that creates positive pressure that prevents air from coming out the supply vent in there. I am wondering if it would be wise to have a new vent installed in one of the upstairs bedrooms in order to alleviate these problems. I reckon I will have to have a certified A/C guy come out and give me some advice. I was hoping that I could find someone on here. hvac air-conditioning ventilation ducts A whistling sound at the return often indicates the grill is too small relative to the duct attached to it. Does consistently leaving the doors open allow the system to sufficiently heat and cool the home? For most bedrooms with more than 100 cfm of supply aor a 1 inch door cut is not sufficient opening for return air. If you have carpet installed it is likely you have less than 1 inch. Transfer or jumper ducts may help alleviate the pressure the home inspector noted.

This can be easily checked with a manometer. The pressure difference between the room and the central area where the return is located should be 3 pa. Experiment by leaving all the doors open (as much a possible) for several days first. If leaving the doors open and/or providing better return circulation does not resolve the issue, then other help is needed. Based on your other it sounds like you need a competent HVAC tech to troubleshoot and balance your delivery system. It is also possible that you are undersized or there are some other issues (like excessive duct leakage, or set up issues) if you are having trouble maintaining the desired thermostat set point.Browse other questions tagged hvac air-conditioning ventilation ducts or ask your own question.DURING humid summers even window air-conditioners that have been cleaned and serviced at the start of the season can benefit from a tuneup before or during the dog days. Most tuneups are easy, take less than a half-hour and can improve cooling.

Begin by making sure that the air-conditioner is unplugged. Vacuum or dust the front grille and controls. Remove the grille to clean or replace the air filter behind it. Some grilles are fastened with screws. amcor portable ac unit partsOthers pop free when pressed along the top or sides. ac split unit autocad blockIf you have difficulty, consult an owner's manual, if possible. ac unit surgingOtherwise, probe with a narrow putty knife around the outside edges for hidden tabs. The filter is a foam or fiber screen attached to the rear of the grille or the front of the air-conditioner behind the grille. Regardless of the severity of the cooling season a filter should be cleaned or replaced every month if the air-conditioner is operated frequently, even if no other maintenance is performed.

Doing so is the most effective step in keeping an air-conditioner performing at peak efficiency. Before removing the filter, check how it is held in place so it can be reinstalled. Notice especially whether one side faces the room. Foam filters are generally washable. Cleaning the type that is fitted in a plastic frame is usually easiest if it is held under a faucet, so that water strikes the cleaner side. That forces the dirt out of the pores on the reverse. After washing, pat the filter with a paper towel or wave it back and forth to dry it. A filter does not have to be completely dry before being reinstalled, but it should not be dripping wet. Replace torn or nonwashable filters. While the filter is out clean the fins on the evaporator coils, the shiny metal ribs on the front of the air conditioner that are visible when the grille is removed. Be careful not to crush any fins. Most are hardly sturdier than aluminum foil. Crushed fins reduce cooling, block air flow and can cause an air-conditioner to emit a whistling noise.

You can sometimes straighten crushed fins by gently twisting the tip of a kitchen knife between them. Professionals straighten fins with a tool called a fin comb. Beneath the fins or near them at the bottom of the air-conditioner may be a small drain that channels condensed water to the rear. If the hole is clogged, clear it by poking it with a wire or a section of a coat hanger. Mold or algae can be removed by wiping with a cloth dipped in chlorine bleach or borax mixed with water. If water is standing in the front half of an air-conditioner check first for a blocked drain. If the hole is clear or there is none, slide a thin strip of wood or cardboard under the front of the air-conditioner, so that the unit tilts toward the rear. That allows water to flow toward the back, where it can evaporate or drain. In humid weather water dripping from the outside of an air-conditioner is normal. The water comes from condensation in the unit overflowing the tray because evaporation cannot dispel it faster than it accumulates.

Examine, clean and lubricate other visible moving parts inside like the flaps directing air flow. Brush parts with a paintbrush to clean them. Use lightweight household oil for lubricating. Then reinstall the filter and grille and inspect the unit from outdoors. Shade helps an air-conditioner cool, but trees, shrubs or awnings providing shade have to be far enough away to allow warm air from the conditioner to escape. As a rule of thumb trim foliage back about two feet in breezy locations and more in corners, where air is still. Clean and straighten the external fins, at the rear, if you can reach them. Finally, inspect any seams and weatherstripping around the air-conditioner and along the window frame. Be sure that the filler panels on the sides of the air-conditioner fit snugly against the sides of the window frame. Install new foam weatherstripping in places where existing strips have come loose, and renew any crumbling putty or caulking compound. Air-conditioners are notorious for developing hard-to-trace noises and other foibles, especially when operated for long periods.

Humming is usually caused by vibration. Look first for loose fasteners that can be tightened. Also check the thermostat, a bulb or wire on the front of the air-conditioner behind the air filter, and reattach it if it has slipped off its bracket. Make sure that the thermostat does not touch the evaporator coils near it. That can cause the air-conditioner to turn on and off repeatedly. If humming continues, try shifting the conditioner's position slightly or inserting shims of foam rubber, wadded tissue paper or even small pieces of wood between the grille and the body. A clicking noise can be caused by the fan's striking the air-conditioner's housing or some other part. Shifting the unit or placing shims beneath it to provide extra support may help. Sometimes loosened coils inside can be tied out of the way with soft wire. If the air-conditioner is old the fan may be worn and need service. If the fan runs but no cool air is produced, the problem can simply be that the thermostat above room temperature.