Weak AC at idle/red lights, sometimes does not start cooling

[NICAT]

Hi Dear Friends.
I have a 2010 Hyundai Sonata with around 350,000 km.
The AC usually starts and cools, but the performance is weak when the car is stopped at red lights or idling. While driving, it works better.
There is also another issue: most of the time, the AC starts cooling normally when I turn it on. However, sometimes it does not start cooling. When that happens, revving the engine may make it start cooling, but not always.
One shop told me the compressor is worn. Another shop said it is very likely the valve on the compressor. (they both connected pressure reading devices during tests. )
Refrigerant level is OK.
I understand that symptoms of a worn compressor and a faulty compressor control valve can overlap. But are there any signs that point more specifically to one of them?
Are there pressure-reading patterns that clearly separate a bad compressor control valve from a physically worn compressor?

 

[The_Jeff]

Have you verified the radiator fan spins when it's stopped with the AC on?

 

[NICAT]

No. Most of the time it starts normally. Just weak performance at traffic light.
so even at full stop, revving up engine improves AC performance.
in case AC fails to start i will check fan.
Both shops confirmed low pressure / flow reading. i think this opts out fans from the list. am i wrong ?

 

[Kira]

Can a receiver/drier or expansion valve clog ?

 

[GMBoy]

The variable rate valve on the compressor is bad. That's a compressor replacement. I see this all the time.

 

[NICAT]

The variable rate valve on the compressor is bad. That's a compressor replacement. I see this all the time.

So it is the valve related issue ?
it is available for sale. At this case compressor replacement would not be required?

 

[mk378]

When it is not cooling, pull over leaving the engine and A/C button on and look under the hood to check if the compressor clutch is engaged. If the clutch has worn the gap between the two parts is too wide, it won't always engage especially when hot. This can usually be fixed without buying anything by taking the clutch plate off and removing some of the shim washers from the shaft.

 

[GMBoy]

So it is the valve related issue ?
it is available for sale. At this case compressor replacement would not be required?

From what I gather from your posts, yes it is. I couldn't be 100 sure because I am not looking at the car with hvac gauges attached etc. With that being said yes is a a compressor replacement as no parts are serviceable. There was one time I did find a valve on ebay and made the swap on a compressor and it worked but no part stores or dealers sell the valve seperate so that was the only time I ever saw that. Your best bet is to have it checked (pay the diag to a shop) and get the bottom line root cause and go that way be it a shop fixing or yourself - at least you would have the problem figured out.

 

[Marcozi]

First step is to check the refrigerant charge levels (high and low). I bet your car is low on refrigerant.

 

[stanlee]

I know on our VW the compressor valve was replaceable ($55 on Amazon) which was 3 year ago. Dealer and a few mechanics wanted to replace the whole compressor of course, then I did my own research. That being said anytime I hear poor performance when not moving the condenser condition comes to mind. That’s what needs to be cooled, unclogged and not leaking (along with a working valve if equipped) to maintain stationary performance once the engine and engine bay are hot.

 

[Highboy]

When it is not cooling, pull over leaving the engine and A/C button on and look under the hood to check if the compressor clutch is engaged. If the clutch has worn the gap between the two parts is too wide, it won't always engage especially when hot. This can usually be fixed without buying anything by taking the clutch plate off and removing some of the shim washers from the shaft.

I don’t think there is a clutch on this model. The pressure valve opens and closes to make pressure.

 

[Chris142]

The ac compressor is worn. It's piston rings are letting refrigerant pass by them at low speeds . Revving it up let's it pump faster and more refrigerant.

If it was the cooling fan Revving it would trip the high pressure cutoff or worse.

 

[Dave9]

Certain vehicles have PCM code that disables the compressor if the engine RPM isn't high enough. Have you parked it, observed the weak A/C but verified that the compressor IS engaged? If it isn't, then I'd research that per your vehicle model, focus on the idle RPM first, what it is vs should be if idling low.

 

[NICAT]

They guy who told "it is valve" seems to be right. He removed valve, somehow repaired it and AC is blowing freezing air now.
Thanks all for support