Hey I had been browsing this site for sometime... any issue I had with my car, I came here and luckily someone had already had the issue and solved it. However, I haven't come across anything similar to what's is wrong now. Hopefully someone here can help out.

It's the start of August in Florida and my AC decided to give out. About 16 months ago I picked up an 05 Acura TL, so maybe it's due for some major parts but otherwise... it's been awesome to me. Last night, I turn my car on and I hear a hissing noise, like a the dull hissing sound that is made you pump air in to your tires. It went away when I turned my AC off. It isn't loud, but you can definitely hear it if the radio is off and you're idle. It also gets somewhat louder if you rev. Immediately, my heart dropped because I know AC's cost a leg to replace and I'm already a struggling college student. But being that it got louder as I revved, I thought maybe it's just a belt. It still blew cold tho so I drove it like like I usually would. This morning, the same thing, hissing noise, and still blew moderately cold, thought okay cool I'll fix the belt this weekend. This afternoon, I get back into my car and its just blowing fire, even on low, and it's still making the hissing noise. When I open the engine bay, I don't hear or see anything unusual but now I'm totally confused as to what it may be. Belt, hoses, freon, compressor, dryer, whole unit... I have no idea.

To sum up, car makes hissing noise when AC is on, was blowing cold, now blowing hot. I apologize in advance for the essay but I wanted to try to get in all the details I could.

Any help or knowledge on the issue would be greatly appreciated.

 

go to pep boys etc... and buy one of those A/C refill kits w/ a gauge.
Then connect it and see if youre full.
If not, you have a leak somewhere.

That's probably the cheapest route to start off with.

 

Thank you, I can definitely do that.

My only issue then is, wouldn't that mean I have a leak somewhere... Or is it possible that overtime I could just get low on refrigerant?

Also, what type of refrigerant is it and do you know the correct pressure?

 

you probably have a leak. I would just take it to a shop to get fixed. Hopefully it's something "easy" like one of the valves (high or low pressure side).

 

Might have blown a hose or a seal and the hissing was the freon escaping.

 

you can not tell how much refrigerant is in the system simply by hooking a gauge up to it. Gauges will give you high or low side pressure readings. There's no way to tell "if you're full" by just looking at the PSI readings. Not to mention it will vary with ambient temperature.

That's what a AC service machine is for. It will tell you exactly how much was recovered from the system.

my advice is to take it to a shop with the proper equipment to service your AC system.

 

Just to update...

I ended up getting one of those refill kits. Started the car, cranked the AC, and got a pressure of zero. Being that compressor is working, I added freon and now the AC runs fine.. Even a couple hours after I put in the freon. However, I'm still not comfortable with the fix and am worried as to why the compressor would just dump all the freon out. I called Honda, who I have a maintenance agreement with to see what they thought and they asked if saw smoke, which would indicate that the freon was dumped. I didn't see any smoke, but I would think a leaky valve would slowly hinder the cars ability to cool it overtime rather than all at once. And apparently if the compressor did do a freon dump, then I have a problem. Hopefully sometime tomorrow, I will take the AC to get diagnosed. I gotta shop around first because Honda's price to check the compressor components of $150 sounds somewhat overpriced.

Thank you all for the input.

 

If the AC clutch relay sticks closed, while the car is running at a low speed, the compressor pressure will spike, and the compressor pressure relief valve will vent Freon, which makes a hissing noise - there is a TSB on this. It usually makes *smoke* but not always - that is why your dealer asked about it.

Don't be confused - the problem (can) occurs on all older Acura/ Honda not just MDX. Don't run the A/C without Freon - if the compressor is damaged, you may have to replace not only the compressor, but other A/C components.

If you want to read more:

https://acurazine.com/forums/showthread.php?t=890420