02 5.9 SLT

Anytime I run the A/C or defrost, I hear a hissing noise coming from behind the dash. It doesn't go away until I turn the blower off. My assumption is that my evap is on it's way out... Please tell me I'm wrong.

 

I've seen this when the A/C system is getting low or old. I'd start by recharging the system before ripping the dash apart.

 

It's been doing this for a while, even last summer after the system was recharged. Could it be a compressor issue? I had to replace the A/C compressor 2 summers ago. I can't remember if it did this before the switch. I was on a 700 mile road trip when the compressor locked up and fried my belt. Luckily we were within a few miles of the lake we were traveling to. I had to buy a rebuilt compressor, even though I've never been a big fan of them. It was the only thing available for miles.

 

The easiest way to answer that question is to pop the hood and check the compressor while the A/C is running. If its not making a noise and the noise is coming from the cab, compressor is fine for now.

I'd take a reading on how much # of freon is in your system with a cheap gauge from Wal-Mart and make sure the system just isn't low.

Although, since you say it does it when the defroster is on, I'm thinking it may be a leak in the evap. I'd go ahead and do the heater core while you're in it if that's the case.

 

Yeah, that was my fear. I don't notice the noise while under the hood, sounds like it's coming from behind the dash. Gonna have to ride this one out for better weather. I've seen posts of these D's with the dash ripped out. Probably have to make a weekend project out of it. Ugh, that means I have to clean out the garage.

 

I would just put up with it and fix it when it breaks........LOL

 

But that also means you "have" to get new specialized tools to do the job.

 

Sounds to me like one of the vacuum controls behind the dash is sticking. If the evap was leaking it wouldn't do it for long if you could here it because it would empty the system of freon fairly quickly. You have to remember when the system is off the pressure equalizes so if it was a leak on the low pressure side of things like the evap it would or at least should leak worse with the system off.

 

I'll just ride it out until something gives. I just like to know what the next mission is so I can plan ahead. In the meantime, I'll just drop some cash on "necessities" like a Fastman TB, K&N drop in and a homebrew CAI. You think my wife will realize they have nothing to do with th A/C? "Honey, I'm doing the best I can. I was told these parts would fix it...". LOL

 

lol its worth a try, let us know if it works