The aircon stopped being cold after sitting for a few days (was working great) - might get a LITTLE cold on the pipe from the compressor but very little ( have another GL I can compare it to)

There are no codes

The condensor fan doesnt seem to run on hi (like the other car when ac is on)

The low side pressure is about 50PSI and it doesnt change if the aircon is on or off (or very little - possibly 1psi but it could just be gauges) - SO IT HAS GAS (they are about the same pressures as the other GL)

In the past I changed the compressor in a W164ML only to find the when I got it out the old one had a bad control valve (which I could have replaced on its own) - it had a bad electrical smell

Does anyone know how to check the control valve? voltages? resistance?

There is also a failure with the low pressure hose into the compressor collapsing and blocking the intake to compressor - I was thinking of getting to the high pressure side check point and putting the gauges on - assume I would get a short spike in pressure until the vacuum in the clogged pipe restricted flow (on start up)

Any thought appreciated

PS I'm in Australia and its a bit warm here now

 

Got some more info

the high pressure side is 101psi. It runs up to about 106psi then drops down to 99-101 and the needle vibrates.

the condenser fan runs normally

i checked pressure on the other (working) GL and it is 90psi (static) and runs up to about 160 then typically 135psi when temperature stable.

Does this sound more like the compressor control valve? Any way to test the valve.

 

Do you have any error codes?
Is the compressor turning (ie compressor will shear at the pully if it jams)?

No error codes and the compressor turning, then it's probably the control valve.

You can just put 12V on the terminals and listen for a click. It's a solenoid. However, only do a quick burst, it's used to seeing a variable voltage, so may overheat with long application.

Control valve is cheap. Gassing is the most expensive part. It's worth spending the $200 just to try. Just remember to bleed as much gas out as possible and just before you take the valve out. Otherwise the residual pressure launches the valve out.

 

Many thanks. Great reply. There are no codes. I disconnected the compressor valve temporarily and i do get a code (so obviously the valve is not open circuit). I have also compared its resistance to a valve in a working car and it is similar. I am still thinking it is the valve. Have not run 12v through it until it’s out.

I put an amp clamp meter and I can see the valve is getting current

I have a valve on order , as well as a receiver drier and a tx valve (it was only cheap).

I am going to remove gas and open system when I have everything (hate the idea of it being open too long)

 

The valve sticks, rather than the solenoid burning out. So the car thinks it's ok, it's applying voltage, but the valve is not moving. If it was burnt out you would likely have an issue on the coil, which the car would pick up (as open circuit or the like). It's also why it sort of gives cool air, because it does move a bit.

 

I did have a mechanic say that he thought the fault was a clogged (or stuck) TX valve, I thought that if that was the case that low pressure side would see a big drop (nearly down to vacuum) as the compressor tries to circulate - I pretty well see no change in the low pressure side - just a small and short duration increase in the high pressure side to about 108 psi (from 100) then it drops back (after a few seconds) to 100 and the gauge needle vibrates. this is when the aircon is turned on.

 

Hey, AC repair is not my strong suit, but luckily the fix has always been the easiest – add more Freon. but I’ve been lucky.

Troubleshooting a defect like this is a logical backtracking of what has changed in the engine bay or the surrounding system. Have you had the AC serviced lately? Have you done any other work? That might’ve disturbed any of the components? Did you run over a curb and slick off the outside air temperature sensors embedded in the front bumper? If the answer to any of these probing questions is no the most likely failure mode is that you have a slow leak of coolant in your system and refilling it to the point of where your compressor will then engage might fix it.
but you’ll still have a slow leak.

Alternatively, if you’re wrong, you will overfill the system and damage it even further.

 

Thanks for reply. I had an aircon bloke put gauges on and it has heaps of gas. Been able to compare with another GL and static pressures similar. Just not enough change to high pressure to make cold.

it’s weird that in US you can still buy freon. In Australia you have to have a license to buy it. Seems overkill. Even a licensed fridge mechanic pays like $150 a kg for it.

 

If they aren't experienced with control valves, they'll have no idea. I believe that the low side pressure should be high with failed control valve. High side will be lower than normal.

 

Just wondering when I pull the valve out if I will lose enough compressor oil to worry about? do you know what oil? Denso have ND oil-8 and I have no idea where to get it....

- I assume if I drain the gas out of high and low pressure sides then I won't have notable pressure behind the valve.

 

I jacked up the car from the passengers side to try and minimise oil loss. I would have lost less than a 1ml. Maybe 3 drops.
i have rear ac, so the guy bleeding said it hard to get all the gas out and expect some pressure. I vented but still had a little pressure push out the valve, but only after I put pliers on it to wiggle it loose. The oring seats tightly.

 

are you right Hand drive too? It seems like a good idea to angle car so the lip around the valve is high as possible in relation to the compressor body.

 

Yeah, just down the road in Adelaide.

 

No worries - hopefully its just the valve - was going to do receiver drier as well just because of the humidity here at present (when I open the system)