Aftermarket A/C system whining noise

[mbres2000]

I recently installed an Old Air Products A/C system in an old Chevy truck. It has a problem that Old Air and I can't resolve.

Symptoms: When the compressor is engaged there's whining noise coming from the inside blower/evap/heater unit, the frequency of which increases with RPMs. Sounds exactly like alternator whine in an aftermarket stereo amp.

What's been tried: The noise persists with the alternator disconnected. And I even bypassed the blower switch, but the noise remains with the blower off and the compressor engaged. Old Air Products tech guys replaced the compressor thinking it might be a fluttering reed valve, but that didn't help at all. BTW, the 28-year old aftermarket system I replaced didn't have this problem, and it's not radio noise.

Also, the system uses a expansion valve, controlled by the temperature of the suction line. Can an expansion valve whine?

I'm at my wits' end, and I think Old AIr just wants me to go away! Any suggestions from you A/C guys?

 

[zrxkawboy]

Could you post a video? I know noises can be difficult to record accurately, but it might help.

 

[JTK]

If it's definitely mechanical vs electrical noise, it sounds expansion valve related.

 

[mbres2000]

Could you post a video? I know noises can be difficult to record accurately, but it might help.

 

[Mechanician]

I have replaced expansion valves for noise. They sounded more so like a reed instrument than a whine.

 

[mbres2000]

Let's try this:
https://photos.app.goo.gl/RBckQMtZ4s2v29AKA

 

[shortyb]

Maybe something to do with the compressor clutch that Old Air uses? Sounds almost like it's causing some sort of ground loop interference noise with the blower motor. Are you sure that the whine increases in frequency in response to increased rpms from the engine? In that video, sounds like the blower motor starts and spins up, then stops almost like the power gets cut, then comes back on again and the whine starts all over.

 

[shortyb]

Does the system use relays? If so, maybe one is opening up or unable to handle the power when signaled and cuts out.

 

[mbres2000]

Maybe something to do with the compressor clutch that Old Air uses? Sounds almost like it's causing some sort of ground loop interference noise with the blower motor. Are you sure that the whine increases in frequency in response to increased rpms from the engine? In that video, sounds like the blower motor starts and spins up, then stops almost like the power gets cut, then comes back on again and the whine starts all over.

They replaced the compressor and clutch. The compressor is even a new model. Looking at their facilities and warehouse stock, I'd guess they sell several systems per day, but are baffled by this one. The blower motor was running at the same speed throughout. In fact, it can have its power disconnected with no change in the whining! Yes, the whining frequency increases with engine revs. Blower motor is running at a steady speed throughout the video, and is much quieter and at a consistent lower frequency. Towards the end, I didn't rev the engine, so whining frequency didn't increase. Crazy, huh?

 

[mbres2000]

Does the system use relays? If so, maybe one is opening up or unable to handle the power when signaled and cuts out.

Yes, there is a compressor relay under the dash. You may be onto something! l'll check it out with a stethoscope.

 

[Chevyc10]

If TXV is restricted you should have high pressure readings. Most TXV that are replaced are because of trash restriction in system. Check pressure of system high and low. If not correct pressure remove TXV check for trash inside.

 

[zrxkawboy]

That is sure a strange noise.

Maybe @Chris142 has some ideas.

 

[Chris142]

That is sure a strange noise.

Maybe @Chris142 has some ideas.

The only thing left is the expansion valve.

 

[bullwinkle]

If TXV is restricted you should have high pressure readings. Most TXV that are replaced are because of trash restriction in system. Check pressure of system high and low. If not correct pressure remove TXV check for trash inside.

A lot of refrigeration TXVs use a strainer on the inlet to catch debris before it can get in. Hopefully auto applications use similar?

 

[Trav]

Yes, there is a compressor relay under the dash. You may be onto something! l'll check it out with a stethoscope.

Maybe the stethoscope would be helpful on the expansion valve?

 

[Mechanician]

It sounds too instantaneous on/off for a refrigerant noise to me.
Is there something like a hose or line that's against the body or firewall someplace?
Maybe it's a resonance from the compressor transferring to the body that wasn't there before something was routed a little differently.

 

[mbres2000]

If TXV is restricted you should have high pressure readings. Most TXV that are replaced are because of trash restriction in system. Check pressure of system high and low. If not correct pressure remove TXV check for trash inside.

Was charged by Old Air, so I'm sure the pressures are good.

 

[mbres2000]

It sounds too instantaneous on/off for a refrigerant noise to me.
Is there something like a hose or line that's against the body or firewall someplace?
Maybe it's a resonance from the compressor transferring to the body that wasn't there before something was routed a little different

Had a retired GM tech I know tell me about that. Hoses are not touching anything, and hard lines to/from condenser go through rubber grommets in the radiator support.

 

[mbres2000]

The only thing left is the expansion valve.

Sure is sounding like it. Will get my stethoscope on it tomorrow.