Hissing sound from Air Conditioner on 97 Accord

I have a 97 Accord with a bit over 200K.
For the past 20K or so, I hear an intermittent hissing sound below the
glove box when the AC switch is activated. Cooling seems to work fine,
verified this summer in the scorching heat of the southwest. Other
than being quite annoying, I am wondering if this is a clue that
something is about to fail.
Thanks

 

Sure you don't have a snake trapped in there?

 

You're probably just hearing the vacuum activated dampers & flaps moving
into place. If it hisses periodically after you start it going, it could be
a vacuum leak or an intermittent contact in the switch.

Check that the radiator (not just the overflow tank) is full to eliminate
the possibility of air bubbles in the coolant moving through the heater
core. It could also mean the charge in your AC is not right, in which case
you're hearing the fluid/gas bubbling through.

Get somebody familiar with that model car to listen to it. Someone who
works on these things for a living will recognize your hiss instantly and be
able to tell you if its a problem or just the nature of your car.

 

The area behind the glove box is right where the A/C expansion valve
resides on your Accord. You are just hearing the sound of refrigerant
changing states from liquid to gas through the expansion valve (it is
a designed-in restriction). IOW, it's normal. If the A/C system
wasn't cooling properly in high temps and the refrigerant charge was
full, then an excessive hissing noise near the glove box would lead me
to believe that the expansion valve was stuck closed - also verifiable
with pressure gauges. You have proven that this is not an issue by
stating that you have adequate cooling in high temp weather.

Toyota MDT in MO

 

We recently replaced a compressor, drier and expansion valve on a
Honda CRV. Had to warranty the damn expansion valve because it made a
piercing whistle! All the while cooling just fine. Thank the good
lord Jap evaporator boxes come out in 20 minutes as opposed to 6-10
hours like on some domestic vehicles.

Don
www.donsautomotive.com

 

Apparently the Japanese have a different lord when it comes to under
dash service. Was this a Nippon Denso or Honda OEM TXV ... or an
aftermarket unit?

Toyota MDT in MO

 

Its probably getting slightly low on refrigerant. IF it hisses shortly
after the compressor cycles on, its probably a frothy mix of liquid and
gas passing through the expansion valve rather than pure liquid as is
normally the case. Nothing to worry about- ALL auto air-conditioners
gradually lose charge around the compressor shaft seal. Its only a
problem if it starts losing charge rapidly to the point it needs a
recharge more often than every few years.

 

Don wrote:

Thank the good

Just for that anti-American remark, I'm bringing YOU my wife's 93 LH car
the next time it needs that job. After all, you're only 5 minutes away
from me

 

I didn't mention heater cores. Heater core removal can really suck on
some domestic vehicles. It can really suck even worse on most ALL
Japanese vehicles. Good thing the Jap heater cores rarely fail!

Don
www.donsautomotive.com

 

It was an aftermarket "AIR" brand from WorldPac. Perfect physical
fit, proper pressures but developed an intolerable whisle about two
days after the car was picked up.

Don
www.donsautomotive.com

 

Don won't mind. After all, it will be on the clock...

JT

 

I suspected as much, but in reality I have no experience with
aftermarket A/C parts on Japanese vehicles. I've always used Toyota/
Honda HVAC parts in the dealers I worked at as well as for indie/home
jobs. It sounds like the high pressure passageway was crimped but not
blocked, or maybe some manufacturing flash was stuck in the path.

Toyota MDT in MO

 

Heater core removal didn't suck on my '75 Corolla. It was pretty easy, in
fact.

The big problem with those puppies was that the heater control valve was
inside the passenger compartment, right above the gas pedal.
And they LEAKED. The damned thing's seals had the sort of lifespan enjoyed
by tadpoles once seagulls have discovered where they are.

Japanese cars didn't start out as good as they are now. Ask me how I know.

 

The 83-87 Renault Alliance/Encore design dispensed with all of that
interior heater control valve crap, and instead opted for a heater
core that leaked in about 99.9% of all cases. (Dash removal
required) Ask owner's legs how they know...

Toyota MDT in MO

 

In my exprience, if you use good antifreeze and change it on schedule...
NO heater cores are very prone to fail. I think I've had excatly one
that ever developed a problem, and that was after 36 years of use.

 

..... and now they own Nissan. <shaking head and walking away...>