Chris - a/c evaporator noise

[MalcolmV8]

Chris, I know you're the HVAC expert so I'll ask you. My buddy has a 1990 Cadillac Deville which was R12. His compressor died so he purchases a reman unit.
Flushed all the lines first, put in a new orifice tube, new drier accumulator, added some oil to the compressor, sealed up system, checked for leaks, and pulled a vacuum for an hour to let everything boil off out of there. Charged system and it seems to work fine.
Approx 85F outside late last night close to midnight. 32 PSI low side, 210-215 PSI high side.
We checked vent temps today while cruising on highway. 100F outside, vent temps got around 44F. Not to bad. My Tundra we measured around 39F so pretty close.

My question is about his evaporator now. It has this weird hissing sound at times. It's internal, not leaking. I've heard this before on vehicles but don't really know what it is or what it means. He never had that noise on the R12 so curious if this is due to the R134 conversion or what the deal is.

Would you have any ideas?

Thanks
Malcolm

[cgrey8]

My guess is you are hearing the refrigerant passing thru the orifice tube. The r134a tubes are bigger and make more noise. My ranger's ac has always hissed even when it was R12.

[MalcolmV8]

Ah ok. So nothing to worry about then. Thanks.

[cgrey8]

The hissing is most noticeable when you turn the car off after running the AC. With everything silent, you'll often hear the hiss continue for a good 20 seconds as the pressures are equalizing. Once equalized, the hissing stops.

[MalcolmV8]

His you can hear it seems sometimes even on highway when driving. Mostly not though. Although in city traffic I noticed it seemed almost each time he let off the gas and we were rolling to a stop. Even on the highway sometimes when he let off the gas you'd hear it.
Although we heard it on the highway while cruising too and even when accelerating in traffic. Mostly the noise is not there, you hear the hissing every once in a while.

[cgrey8]

I wonder if you hear it more because it is a Cadillac? Caddys are probably a lot more sound insulated than a lot of other vehicles. And with the Evaporator being right in the cabin with you, it's difficult to disguise the hiss from the evap. Also if he removed a decorative baffle from the passenger side floorboard, it could've also been doubling as a sound baffle, particularly if it had padding on the backside of it. If the car dates back to the R12 days, then its very possible some sound baffle that went around the passenger side floorboard has been removed and never put back...and thus why the hiss is more prominent than it would otherwise normally be.

I've also heard of "self adjusting" orifice tubes. If there's any chance he got one of them, those could be making a bit more notice than static tubes would too. They sell them as upgrades, but I believe they are noisier.

[MalcolmV8]

Never heard of an adjusting orifice tube but most interesting. Thanks for all the info. I'll pass along.

[plowboy34]

the hissing noise in a conversion is not abnormal Malcolm. I do not know why some cars do and some dont but my 93 A/Star hissed bad. It cooled just as good as R12 but was noisy. I have done a few buddies and it's about half ands half on the hiss. I justy racked it up as one of them things.