need help unique AC issue

[Benz300]

Hello everyone,
I have been struggling with this for a few months now and mechanics can't figure it out so i thought I would ask the gurus here.

2000 S500 with rear a/c.
new ac compressor and freon filled correctly by indie.

problem: when the car starts in the morning, the ac works perfectly. however once the car is turned off and turned on again within 5 minutes, ac simply doesnt work. no matter what the settings.

if I let the car sit for an hour and start again, ac works perfectly again with cold air as it should.

Had the ac pressure checked, when ac is working normal, the low port and hight port readings are perfect, shut down and restart car, no ac, and the pressure at lo port is really high.

any help / advice will be appreciated.
I already checked the codes from the ac panel inside the car through the secret menu and there aren't any codes, i did however reset the acc control unit numerous times.

thanks again in advance

[ILUVMILS]

Two questions:
1. Are the high and low side pressures the same when A/C isn't working?
2. Did you have the same issue before replacing the compressor?

[Benz300]

Originally Posted by ILUVMILS

Two questions:
1. Are the high and low side pressures the same when A/C isn't working?
2. Did you have the same issue before replacing the compressor?

Thanks for the reply. I'm not a mechanic but more of a diy... But I'll answer to the best of my knowledge.

Yes when the ac isn't working the pressure is high on both sides, when the compressor does work, I see the low port pressure drop right away and stay low.
Had the same issue before replacing the compressor as well.

[oldsinner111]

people are whimps these days,I never use ac,its been broke 7 years,and I don't care.Waste of fuel.

[INSIDIOUS]

Might help to let it run at a warm setting before shutdown, maybe last minute of driving. That should let the stuff evap and the compressor won't provide a surplus. just a WAG.

[Benz300]

the problem is :
ac will work fine for hours doesnt matter but once I use the ec button to turn the compressor off, and then turn it on again, the compressor simply doesnt engage again. Until, i park the car and start after half hour, the the compressor will work with ec off mode untill i try to turn the ec off button to turn the compressor off.

That, or if i don't even touch the ec button and simply keep the compressor on all the time, once i park the car even for a minute, and turn the car back on, the compressor won't engage.

somehow, the car needs half hour or more to engage the compressor back on...

[TX76513]

If the compressor is not engaging (or cycling) then its an electrical problem. You need to perform further testing but a known problem on your car is the evaporator temperature sensor. With that said its a good place to start and a failed evaporator temperature sensor would cause the condition you describe.

[Benz300]

Originally Posted by TX76513

If the compressor is not engaging (or cycling) then its an electrical problem. You need to perform further testing but a known problem on your car is the evaporator temperature sensor. With that said its a good place to start and a failed evaporator temperature sensor would cause the condition you describe.

is there a good way to check the sensor before i change it ?
thanks.

[97 SL320]

Originally Posted by Benz300

Had the ac pressure checked, when ac is working normal, the low port and hight port readings are perfect, shut down and restart car, no ac, and the pressure at lo port is really high.

If after restart the low side has high pressure, this is typical if the compressor isn't running. ( the system will have equal pressures on both sides if it isn't running. )

Your issue seems AC control panel related not mechanical. You should be able to get live data out of the control, anyone know if this is still possible? On my 97 with the system on , press REST until the display changes then use the hot / cold buttons to scroll through the info.

[Benz300]

bump, any further help will be appreciated...

[INSIDIOUS]

What we need is the troubleshooting procedure for that evaporator temperature sensor. What sort of readings should we expect on our multimeter?

[Benz300]

how can i access the evaporator temp sensor ? where is it located and how do i replace it. thanks.

[Benz300]

an update for other who might have the issue: I basically bought another new compressor, new receiver dryer, evaporator pressure sensor, evap temp sensor and had the indie do a complete suck up of the old freon first, with new PAG oil for the compressor as well.
Must've been one of these parts, but for the sake of saving labor etc, after replacement of all these parts AC is now working perfectly

[Diseasel300]

Sorry to say, but not a very honest Indie if he did all of that work for a control issue. That's a lot of money to throw at a system that seems to work properly except for certain operating criteria. Evap temp sensor isn't expensive and should have been the first thing to try before tearing apart a working system.

[97 SL320]

Given modern AC compressors are variable displacement, I'm wondering if the control system stuck and kept the compressor at low displacement after a shutdown.