Shut it off: hissing can mean a refrigerant leak

Why this happens

Trane says hissing is not a normal sound. A hiss near the indoor coil or the refrigerant lines can mean a large refrigerant leak, and a hiss underneath the normal sound of a running outdoor unit can point to compressor or electrical trouble. In both cases Trane says to shut the system off and call for service. Bryant lists hissing among the warning signs of a potential mechanical or refrigerant issue, and Lennox says prolonged hissing could indicate a serious problem that calls for immediate attention from an HVAC professional.

What to do right now

1. Rule out gas before you touch anything. If you smell gas or rotten eggs, or the hiss seems to come from a gas furnace, a gas pipe, the gas meter or another gas appliance, skip the steps below. Leave the house and call 911 or your gas utility from outside. DTE Energy says to leave right away if you smell or suspect a gas leak.
2. Set the thermostat to Off. Trane says running an air conditioner with a refrigerant leak can do further damage to the system and to the environment.
3. Leave the panels on the indoor and outdoor units closed. Bryant says not to disassemble the outdoor unit or handle electrical or refrigerant components yourself.
4. Don't try to top the system up. EPA says only Section 608 certified technicians can purchase refrigerants intended for stationary air-conditioning equipment.
5. From the outside, look along the refrigerant lines and fittings for an oil stain or oily residue. Trane lists that as a visible sign of a leak. Look only, and don't touch the lines or fittings.
6. Call an HVAC technician and keep the system off until it is repaired.

When to stop. If you smell gas or rotten eggs, or the hiss seems to come from a gas furnace, a gas pipe, the gas meter or another gas appliance, leave the house and call 911 or your gas utility from outside. DTE Energy says gas leaks often make a blowing or hissing sound, and that you should not rely on your sense of smell alone.

Start this troubleshooter over

FourHome is our sister brand. Browse all FourHome replacement faucet and shower parts on the FourHome Amazon store. We earn from purchases made through this link.