AC Hiss on First Use of Day

[Tigg]

I've had cars which leaked freon before. They usually would hiss constantly with the compressor cycles. This time though it only is happening with first use of AC each day. Other than that its cold, does this signal freon is getting low?

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[ShadowsPapa]

I've hard cars which leaked freon before. They usually would hiss constantly with the compressor cycles. This time though it only is happening with first use of AC each day. Other than that its cold, does this signal freon is getting low?

Refrigerant leaks typically don't hiss. Not the leak itself - just the fact that it's low which may result in different sounds.
Hissing on first use may only mean the gas is moving through the system, nothing more.
If you had a leak, you'd not hear the leak - unless it was huge then the AC would stop working after a while as it doesn't take much time for a hissing leak to drain an AC system.
You are likely hearing normal operation as the compressor compresses, and things move through the lines and valves.
I've never heard a modern vehicle's AC hiss, but then maybe it's because I'm so used to the normal sounds, I simply tune them out.
If it's blowing cold, it's not low.

 

[Pilsner]

Refrigerant leaks typically don't hiss. Not the leak itself - just the fact that it's low which may result in different sounds.
Hissing on first use may only mean the gas is moving through the system, nothing more.
If you had a leak, you'd not hear the leak - unless it was huge then the AC would stop working after a while as it doesn't take much time for a hissing leak to drain an AC system.
You are likely hearing normal operation as the compressor compresses, and things move through the lines and valves.
I've never heard a modern vehicle's AC hiss, but then maybe it's because I'm so used to the normal sounds, I simply tune them out.
If it's blowing cold, it's not low.

This. The pressure sensor would stop the clutch from engaging with very little loss of pressure. You are condensing and evaporating a liquid/gas, so there is some noise to be expected during that process.

 

[swtrailboss]

I've had cars which leaked freon before. They usually would hiss constantly with the compressor cycles

Yes you are absolutely correct when the system gets low on refrigerant you will hear a “hissing” sound coming from the expansion valve in the evaporator (under the dash area) while the compressor is engaged …usually the system won’t cycle on and off when it is low and every so many seconds you will audibly hear the “hiss” noise again.
As shad papa says what you hear is likely normal IF you only hear it once at the system start up as you have described.
Pulling an AC system from an equalized pressure to the norm HI and LOW side pressures create this noise louder in some makes of cars than others.
As Pilsner said if the system gets too low then the pressure switch won’t allow the compressor clutch to engage.

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