Air Con making a very (very) high pitched noise

Hello all,

Hot weather, air con on, no cold air! Typical.

It was re-gassed last summer, and I usually leave it on all year round, so it may have stopped working a while ago but I haven't noticed it because I needed warm air, but I can't see any sign of leak detection dye anywhere, and I know it's in there so I don't think it's that.

What I do have is a very very high pitched noise that disappears when I turn the compressor off. It's right up around my tinnitus, almost sounds like it could even be electrical interference.

The compressor clutch is working fine and the compressor kicks in as you'd expect, but I can't hear the high pitched sound when I'm under the bonnet listening there, so I don't think it's a failing bearing or anything like that.

The only other thing I've noticed is if I listen carefully inside the car to the centre vents, when turning the air con on I get a sound that sounds like a fan starting up, it stops when I turn the air con off again. Perhaps that could be the blend motor, I'm not sure.

I have no book symbol, and on the face of it everything works as it should.

Is there the possibility of a dud HEVAC unit that has a failing electrical component and that's what I can hear? The sound is the same as the old CRT TV my mum had when I was a kid!

MrGorsky said:

Hello all,

Hot weather, air con on, no hot air! Typical.

!

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Sounds right to me, Hot weather, aircon on, no hot air Cold is what you want.

Datatek said:

Sounds right to me, Hot weather, aircon on, no hot air Cold is what you want.

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Ha! Yes I may have that bit backwards! I'm a very confused man.

If you set the HEVAC to manual and set the temperature on both sides to LO, do you get the same temperature both sides? Is it above or below ambient?

It's very slightly below ambient. Same on both sides.

What does this tell us?

MrGorsky said:

It's very slightly below ambient. Same on both sides.

What does this tell us?

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That the blend motors are working

Well that's one thing off the list.

I suspect it's an electrical problem with the HEVAC unit.

The backlights have been dimming slightly when I press the brake, and the fan control has been temperamental for ages.

I've read a few places that they get dry joints etc so perhaps I should take it out and have a look inside for signs of failure.

Do you know if a Nanocom will operate the HEVAC controls even if the HEVAC unit is faulty? I could plug in and see if I can get cold air with a Nanocom, that at least might tell me where the problem is.

MrGorsky said:

Well that's one thing off the list.

I suspect it's an electrical problem with the HEVAC unit.

The backlights have been dimming slightly when I press the brake, and the fan control has been temperamental for ages.

I've read a few places that they get dry joints etc so perhaps I should take it out and have a look inside for signs of failure.

Do you know if a Nanocom will operate the HEVAC controls even if the HEVAC unit is faulty? I could plug in and see if I can get cold air with a Nanocom, that at least might tell me where the problem is.

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That would depend where the fault (if any) lies within the HEVAC.

Datatek said:

That would depend where the fault (if any) lies within the HEVAC.

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I have the older type of HEVAC. Does that mean the control unit in the car directly switches the compressor on and off? And the fans too?

MrGorsky said:

I have the older type of HEVAC. Does that mean the control unit in the car directly switches the compressor on and off? And the fans too?

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Where is the noise coming from, expansion valve can cause that sort of thing.

wammers said:

Where is the noise coming from, expansion valve can cause that sort of thing.

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Quite hard to tell a direction, but from behind the centre console I'd say. It's so high I can only just hear it to be honest, but it definitely comes and goes with the compressor being turned on and off.

Can I give the expansion valve a knock or something to see if it's sticking? Does it even work like that!?

MrGorsky said:

Quite hard to tell a direction, but from behind the centre console I'd say. It's so high I can only just hear it to be honest, but it definitely comes and goes with the compressor being turned on and off.

Can I give the expansion valve a knock or something to see if it's sticking? Does it even work like that!?

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You can try it. But if it's coming from the area you say most likely that is what is causing it.

Well tapping the valve didn't make anything cold happen.

One side of the pipework from the compressor gets very hot though, (the smaller pipe) so I assume the compressor is doing it's job?

Compressing a gas would indeed cause heat and then need cooling in some sort of radiator.

It was taken today to ATS for re-gassing.

They confirmed it was almost empty,. They also had a record of how much they put in last year and they said they wouldn't expect it to get so low so quickly, so there is a leak somewhere.

They also said they couldn't detect the leak in the engine bay so refused to fill it because the leak might be in the car and they didn't want to gas us!

On the plus side they said if I took it back tomorrow morning first thing they'd lend me the UV light to crawl around until I found it.

On the minus side, if they couldn't see the leak in the engine bay, and the leak is in the cabin, doesn't that mean I'm going to have to take the dashboard out to correct it????

God.

If it comes to that I suppose changing the blend motors and greasing the flaps would be a wise idea too...

MrGorsky said:

It was taken today to ATS for re-gassing.

They confirmed it was almost empty,. They also had a record of how much they put in last year and they said they wouldn't expect it to get so low so quickly, so there is a leak somewhere.

They also said they couldn't detect the leak in the engine bay so refused to fill it because the leak might be in the car and they didn't want to gas us!

On the plus side they said if I took it back tomorrow morning first thing they'd lend me the UV light to crawl around until I found it.

On the minus side, if they couldn't see the leak in the engine bay, and the leak is in the cabin, doesn't that mean I'm going to have to take the dashboard out to correct it????

God.

If it comes to that I suppose changing the blend motors and greasing the flaps would be a wise idea too...

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You are going to struggle to crawl under the dashboard where the evaporator is. And yes dash out to remove heater unit.

wammers said:

You are going to struggle to crawl under the dashboard

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The ATS guy seemed to think that I'd see evidence of the leak clearly, even if it was behind the dash. He said he was going to add a UV dye that would show up easily under the light.

Plus he's got some probe that detects the gas that I can shove down the vents too.

Lets hope it's a stone chip in the condenser....not a pin hole ion the evaporator!

MrGorsky said:

The ATS guy seemed to think that I'd see evidence of the leak clearly, even if it was behind the dash. He said he was going to add a UV dye that would show up easily under the light.

Plus he's got some probe that detects the gas that I can shove down the vents too.

Lets hope it's a stone chip in the condenser....not a pin hole ion the evaporator!

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Top left hand side of condenser looking from front of car would be favourite leak point. If it is leaking and you get a new one, spray this area with alloy wheel paint or silver HT exhaust paint.

Spray the condenser for preventative maintenance? Noted.

Well done Wammers. The UV light shows a leak from the top left hand side of the condenser.

Go and see matron for an extra bit of tuck.

I'm going to get a new condenser ad fit it, and change all the O rings on the system whilst I'm at it.

Is there a condenser manufacturer to avoid like with the radiators? And am I going to run in to seized joints that will strip my threads whilst I take them apart, and require me to buy new hoses like with the oil coolers?

Anyone done this before?