my heat pump outside is working but my central air conditioning/heating unit in the garage makes a hissing sound or faint sound of water running. There is air coming from the vents. The very last time I used the heat, about a month ago the same thing happened but when I switched to air conditioning the last month, it worked until now. What are the possible problems?

  • It would be nice to know whether the diagnosis was capacitor, coolant, or if you just decided to replace it without resolving the cause.
    – keshlam
    Dec 30 '14 at 15:29

If all is well with your outside unit, I would double-check your AC coil in the main unit indoors. It could be frozen over and thus not cooling the air. This same exact thing happened to us about 3 weeks ago. We moved into a "new" house (new to us anyways, haha) and not many things were being taken care of well... in simple terms, a freeze-over like this can happen because the coil drain is clogged with dust particles and/or sludge. This means there's no where for the condensate to go and leads to a frozen coil. Hopes this experience can help someone avoid a big maintenance bill in the future! To fix the issue, use a hair dryer or heat gun to melt the ice away. DO NOT CHIP AWAY at the ice since the coils are very delicate and you could puncture one easily.

  • 1
    Frozen lines are usually due to a lack of coolant in the system.
    – Doresoom
    Jul 29 '15 at 13:29

It sounds like you are low on refrigerant or you have a failed compressor. This is not something you can fix yourself. Call for service.


This might be an easy fix. Go look in your air conditioner, there will be a capacitor which is cylindrical shaped. If it is puffed out or distorted in shape, it needs to be replaced. You can replace this yourself. My suggestion is to first take a picture of how the wires are connected and it's simply plug and play. Take the old capacitor to the supply house so you get the right replacement.

  • Want to add the obligatory warning that power should be secured before going into the unit. Capacitors can maintain a charge even with the power off, please be careful and measure both power applied and power remaining when playing with the cap!
    – N8sBug
    Sep 26 '15 at 23:02

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