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Discussion Starter · #1 ·
AC/defroster use gives me a low hissing sound lasting about 5-10 seconds, only when the AC or defroster is use, sitting or driving, fan speed does not affect this, theres no specific timing to it but seems to occur about every 2-4 minutes.

Is this the Freon charge low, or this indicative of something more sinister?

And and all insight appreciated.

Thanks, AC knowledge is the least of my skills.
 

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You are hearing the compressor cycling and freon circulating into the evaporator. Some cars seem to be louder than others.

If you are concerned you can take it get checked. Take it to a shop that uses an actual freon recovery machine. They will measure the amount withdrawn from the system and compare it to the actual charge needed. The machine will then vacuum and do a leak test.
 

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As stated, fairly normal sound of the Freon working through the system. there is an expansion valve that is the change over point from high pressure liquid to low pressure liquid. The low pressure liquid boils at low tempertures and pulls heat with it. As the liquid goes through the tine hole in the expansion valve it sounds like a hissing spray inside metal, which is exactly what is happening.

You can have it checked, but you will probably just spend money to find everything is normal.
 

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Well mine kind of hisses when it is turned on. Im 90% sure it is normal. But it never makes hissing sounds after that...
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Gauges are a real shot in the dark when it comes to measuring the actual freon level. It is better than nothing, but not in the same ballpark as a recovery machine. Out side temps, airflow through the condenser, humidity etc play a huge role in altering the readings of the gauges.
 

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One thing a gauge will do that a recovery system can not is test how well your compressor is working. Once you know you have the correct charge in the system test both high and low pressures. When a compressor starts to have blow by the pressures will drop and performance goes down. It sounds like yours is working fine, mine does the same thing when the temps are in the 50's and 60's, when it is warmer out the compressor runs almost all the time when either defrosting or cooling, so it does hiss a bit.
 

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Discussion Starter · #8 ·
After I was able to get out of work last evening, I did some more checking. Seems the system is NOT blowing cold, and it sounded like the compressor was not engaging. I know without the freon charge being in the system the compressor clutch will not engage.

It's off to the mechanic next week to check for dye test for leaks and repair.
 

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Check the lines where they enter the firewall. Mine were slowly leaking there. I replaced the o-rings and all is good. The system is factory charged with dye. Look for a a yellowish green tint on the lines, compressor and condenser.
 
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