Hissing noise from blower motor area

[Towncivilian]

I sometimes get an audible hissing noise when running the A/C. I never noticed this before applying the TSB to quiet the blower motor ticking. A/C still blows nice and cold. What should I check? I will ensure that the blower motor's small plastic hose is on tight on both ends, and maybe change the filter soon as it's getting nasty. Anything else to check?

[ARKQX33V6]

Blower fan, cage type as in our Qs can be noisy and the reasons are similar to HVAC equipment.

Dirty fan
Worn or dry bearings
Blockages
Failing motor
Differential pressures across the fan

Restrictions before at or after the fan and this part is critical as air flow changes going to the fan then going through the fan and leaving the fan. A dirty scroll cage will change things. So will a blocked or partially blocked duct.

Operate the fan to hear the noise then change the venting and listen, windshield, floor, top vents, you may tell which duct system may have a blockage.

When the motor is failing the extra noises it makes often affects the sound operation.

But if the noise is caused by the actual air flow an investigation is needed, look for blockages, for parts moving and blocking like deflectors. Dirt build up changes the inlet/outlet duct size to smaller, and this could increase the air speed causing noise.

I think a tear down and cleaning may be needed and if your car as an in line filter change or clean it.

[Towncivilian]

I recently cleaned my squirrel cage (as evidenced in my linked thread) and there was no debris, just quite a bit of dust that was removed. I used a sink, so perhaps some water got into the bearings - but like I said, I only hear this hissing noise when the A/C is engaged. I'll try other duct settings with A/C on to see if the noise changes. However, I also hear a hissing noise around the transmission fluid dipstick, which is also where the A/C low pressure line is IIRC. Due to the amount of noise present when the engine is on I wasn't able to pinpoint where the hissing was coming from exactly.

[ARKQX33V6]

Hissing may be related to AC.
1st, cold air is denser and will cause more noise while moving.
The AC goes through a transformation from liquid to gas and back. The trnsformation either way could be hindering. There is or should be a drier near the condenser, the rad, using your hand feel it, then using your ear listen to it, is it noisy? It may need a change.

Run your fan at full speed with ever increasing temperature and then ever decreasing temperatuire setting and listen for the noise. Now repeat the process with the AC turned on, wait for about 5 minutes then full speed at the coldest, take the temp up and adjust the fan speed lower, listen to all speeds inside and outside with the hood up. When do you hear the noise the loudest.

Get back to us.

Bearings on the fan should not be affected by water, but with that said anything is possible. You could remove the fan and check the bearings, even grease them again, but are they bearings or bushings, if bushings anything with noise is possible.

Your description to me of hissing is that of noise via air movement and air moving does cause noise, again you have to check if smething is in the way like a shutter or flap that should not be.

Happy hunting!

[yeldogt]

Normally, the hissing is cause by a slightly low refrigerant charge. It comes from the expansion valve.

But, both of mine do it to some degree and I know they are properly charged. Mine can almost sound like a rattle at times. Both of mine are LE's with ACC.