How to keep your cool: when HVACs go wrong.

What can go wrong usually does. Repairing a HVAC system when it breaks can be simple once you know how it works and what things to look for. HVAC systems fail for many reasons. They get old, they withstand damage from cars and kids, they were installed incorrectly, or there was improper preventive maintenance performed. There's nothing worse than a broken HVAC in the peak of summer. Following are 45 common HVAC issues--and 45 answers to help keep residents cool.

1. No cooling; nothing works inside or outside.

Make sure the thermostat is set to cool and automatic. Is the breaker tripped? Reset (flip) the breaker off and on firmly twice and see if power is restored to the unit. This may also indicate that motor windings are beginning to fail. If there has been an electrical storm or power surge, the unit is probably OK, but if the breaker keeps tripping or won't reset, you may have to plan for a new unit. If the thermostats are mercury type, is there a spark when the temperature lever is moved?

Make sure the unit is receiving a full voltage supply of 208 or 240 volts. Make sure the system is receiving line voltage to the transformers' primary winding and that the transformers are supplying the proper secondary voltage.

Check the evaporator coil; it may have ice build up. Sometimes the ice can be so thick that air is completely blocked.

Jumper the thermostat from R to G. If the interior fan comes on, the thermostat is defective.

2. No cooling; interior fan is turning.

Although you hear the fan turning, it might not mean that it's blowing air. The evaporator coils could be frosted because of a low or improper charge, a dirty filter or some other restriction on the air stream. There might be ice on the evaporator coil or on the evaporator area, blocking the air flow. Any time there is ice on the evaporator, turn off the air conditioner and operate the blower only. Never run the heat to defrost the ice--that will damage the heating parts.

If the thermostat calls for cooling and the inside fan is turning, check for low voltage at the condenser unit. If there is low voltage going to the units, check the outside primary voltage supply.

Make sure the outdoor condenser is coming on. If it's not, check the contactor to see if it's engaged. If the contactor is engaged, the fan motor and compressor should be running. If the fan is turning, the compressor should be running, too.

If the outdoor fan motor is turning but the compressor is not running, check the run and start capacitors, ensure the relays are good and the high and low pressure switches are both closed.

3. No cooling; compressor not turning; outdoor fan motor on.

If the outside fan is turning but the compressor is not, carefully feel the compressor. The compressor may be hot enough to burn your hand. If it's hot, the compressor has been running but has stopped because it has overheated.

Check the compressor run capacitor. Check the unit's charge. Check for stoppage in the sealed refrigerant system. Check for loose wiring on the contactor or compressor.

If a unit is turned on and off too rapidly, it might have a safety switch that prevents "short cycling." Or, it might have shut off on overload and it might take time for it to come back on.

To cool a compressor more quickly, run a trickle of water from a hose over the compressor or use a bag of ice. Make sure to lockout or tag out the system first.

If the compressor is cold to the touch, check for bad starting components, contactor, relays and open or shorted motor windings.

4. No cooling; compressor on; fan not turning.

Make sure the fan blade is not blocked and that it can turn freely. If there is nothing blocking the blade, the fan motor run capacitor might be out, the fan motor might have burned out or the contactor might not be engaging properly. Check for loose or burnt wiring and for open or shorted motor windings.

5. No cooling; heat is running at the same time as cooling.

The axillary heat is on, too. The sequencer or relay is stuck in the "on" position or the thermostat may have a fault.

6. Outdoor fan motor turns slowly when condenser is off.

Check the contactor--it may be stuck closed. Check and replace the outdoor fan motor, as might be shorted internally.

7. Swollen capacitors.

Capacitors can swell when they're old. Replace them.

8. Compressor makes a hissing or steaming sound like a car radiator.

Excess charge is causing the compressor's internal pressure relieve valve to discharge, or the compressor is damaged internally.

9. Compressor sounds like it's knocking.

Check for loose panels or missing screws. Inspect the compressor installation grommets to ensure they're in good condition. Make sure the condenser unit is level, which is necessary for proper oil circulation. If the unit is level, you may need to add compressor oil.

This wasn't a problem until technicians started recovering the liquid out of the machines. Now, if the technician doesn't add exact amount back into the system, the compressor may knock after liquid recovery.

10. Compressor kicks on and then immediately kicks off.

There is a bad run capacitor or burnt, damaged or loose wiring or bad run winding.

11. Bad run winding on the compressor.

The compressor is defective and must be replaced.

12. Condenser vibrates.

Check the condenser fan blade for damage and the fan motor for bad bearings. Make sure the rubber grommets that secure the compressor are not worn and that the compressor isn't loose.

13. Unit rattles.

Make sure the condenser unit is level. Check the condenser fan blade for damage and the fan motor for bad bearings. Check the panels and cover plates for correct installation. Check for missing screws.

14. Small liquid line is very hot.

The condenser may just need cleaning or there might be an improper refrigerant charge in the system. Or, there may be a high load requirement.

15. Condenser or suction lines are iced up.

There is an improper charge or airflow in the system. See No. 1 or 2 for suggested remedies.

16. Slight freezing on suction line.

There is an improper charge or airflow. The filter may begin to load restricting airflow slightly, causing the unit to frost.

17. Suction line is dripping water.

This is usually normal; however, excessive condensation can indicate an improper charge. Ensure the suction line insulation is continuous and serviceable.

18. Suction line is very hot.

There might be a stoppage in the lines or a light load on the evaporator, or the unit is undercharged or has a leak. If the unit is a heat pump, it may be running in the heating mode. Check the thermostat, control circuits and control wiring.

19. Indoor fan motor stops running.

If the outdoor fan motor is still operating, check the indoor fan motor capacitor. Make sure there are no burnt or loose wiring connections, check the fan relay, clean the fan motor and test the motor windings.

20. Inaccurate thermostat.

Make sure the thermostat is level and calibrated and that there are no holes behind the thermostat or drafts that are making its readings inaccurate.

21. Thermostat stays off too long before coming back on.

There is a bad cooling anticipator on the thermostat.

22. System just doesn't cool.

Check for improper charge, dirty filters and if the return air or the furred down (drop ceiling) has lost its seal. Check the apartment infiltration through cracks around doors and windows. There might be a wrong fan speed being used, a blower blade on backwards, a dirty evaporator, a dirty condenser, mismatched units or mismatched SEER values. Or, it may just be too hot outside.

23. Refrigerant oil on lines or unit.

There is a refrigerant leak or possibly a deminimus release.

24. Unit loses its charge.

If a system needs charging, there is a leak. The size of the leak will determine the length between charging. Use soap bubbles and electronic or ultrasonic leak detectors to find the leak.

25. Starting components go bad.

Look for loose wiring and ensure the parts being used are those specified by the equipment manufacturer. An oversized system can cause starting components to fail prematurely.

26. Utility bills are too high.

Inspect for infiltration from doors, windows, outlets and flue. Check the system charge and clean the evaporator and condenser. Check the return air or furred down seal. Make sure only that apartment is supplying electricity to its HVAC system.

27. Apartment interior has wet spots.

Check for drip pan stoppage, drain line stoppage and worn out or damaged suction line insulation running thorough the walls or ceiling areas.

28. Interior fan makes a scraping noise.

There is a dirty system, unbalanced fan blades or bad motor bearings. This can also be caused by poor installation.

29. Interior fan motor makes a "thunk" when starting.

The motor bearings are worn out or the system panels are loose.

30. Interior unit hisses during operation--not the usual rumble sounds other units make.

The system is improperly charged. Gas vapor is being fed to the evaporator instead of liquid.

31. Apartment cools unevenly.

The interior registers need adjusting. Slightly close the air register vents in other rooms to increase the airflow into the rooms that aren't cooling as well.

32. Evaporator makes buzzing sounds even when off.

There is a defective transformer.

33. Excess condensation forms on the drip pan or surrounding areas.

Excess condensation can be caused by improper air flow, wrong fan speed, dirty system, loose panels, missing insulation or extra humid conditions.

34. Air register condensation forms.

This can be caused by many things: a blocked or dirty evaporator, improper duct insulation, gaps or loose connections in the duct, gaps or loose register where it attaches to the duct, the air flow to that duct or register is blocked or restricted.

Bathroom registers usually condensate the most. With such a high temperature difference between the actual temperature of a metal vent and the high moisture content in the bathroom, moisture tends to collect at these registers the most.

Many times the problem is that the vent isn't insulated between the ceiling and the branch duct that it's attached to. Most of time, the vent can be removed and reinsulated.

35. Identifying furred down leaks.

Try the suction test. Hold the A/C return filter near the return grill opening. The filter should be pulled with a vacuum toward the opening. Look for light. Turn off apartment lights and close the doors to make it dark as possible inside the unit and look up into the furred down for lights from the attic area. This is best done on bright, sunny days or with bright lights inside the attic area.

Examine the attic area. Visit to the attic and look for holes that may be hidden behind the plenum or supply duct from the underside access panel. Look at the insulation and make sure it is even and not caved in. Look for insulation inside the furred down area or on the evaporator or fan motor that is a good indication of a hole.

36. Thermostat reads inaccurately.

The thermostat must be level or it won't work. Check if the wiring hole behind the thermostat is unsealed, which can allow inside wall air to affect the thermostat reading and operation.

37. Return filter is never dirty.

If an apartment home's air conditioning return filter is never dirty, the evaporator may be pulling air from other locations besides the return vent. Check for a loss of furred down seal and air leaks in the return system.

38. Return filter is always dirty.

Excessive dirt and lint on return filters can be an indication that doors and windows need weather-stripping or that there are holes in cabinets and around plumbing fixtures. Look for traces of dust pile-ups around cracks and crevices. Check switch and outlet plates for air seeping in.

39. Condensation drip pans on the interior evaporators back up.

Using algaecide tablets in the drain pan will help to prevent the slime build-up that causes most condensation leaks.

40. Air coming from the vents smells stale.

Most smells are from dirty systems or dirty condensation pans and lines. Clean the evaporator unit and pan. Add algaecide tablets to the condensation pan. You may want to check the air distribution system, too.

41. Air coming from the vents makes a whistling sound.

Open the vent louvers all the way. Check all vents to see if any are closed or are blocked by belongings. Make sure the fan motor is the correct size.

One of the best places to adjust the airflow is at the dampers at the trunk duct.

42. Most of the vents are blowing water as well as air.

First, clean the system and retest it. If that doesn't work, look for air leaks in the air supply duct work.

43. Every time the A/C comes on, a pipe rattles in the wall.

Cut the wall out where the noise is located and install tie down brackets on the pipe to keep it secure. Also consider checking non-condensibles or the refrigerant charge.

44. Outside unit overheats when it gets hot outside.

The unit might be overcharged or it may have a weak overload inside the compressor.

45. System turns on and off too much.

This can be caused by air leaks from doors and windows, an oversized system or a defective thermostat.

BY DON WILLARD, CAMT 

Don Willard, CAMT, is an award-winning speaker and a consultant to Apartment Association of Greater Dallas and NAA. Willard owns a maintenance consulting business, is a maintenance software developer and an inventor He has been actively involved in the Certified Apartment Maintenance Technician (CAMT) program since earning his designation in 1992 and teaches CAMT classes across the country. He is also a member of the NAAEI Faculty. Air Conditioning Contractors of America (ACCA) also contributed to this article. For more information, visit www.acca.org.