W204 aircon pressure sensor faulty
Discussion
I know this is a long shot but does anyone know what resistance the sensor should put out if the aircon is gassed up. I have looked at my mats car this morning and the gas pressure is fine, about 100 psi with the engine off. I suspect its the pressure sensor but its a 3 wire one and obviously not just a straight on or off switch, it must send various readings back to the ECU when its firing up. If you press the air con switch it just flashed red 3 times and the compressor doesn't kick in.
I was thinking of bypassing the switch by connecting the correct value resistor to it instead to see if it works.
I was thinking of bypassing the switch by connecting the correct value resistor to it instead to see if it works.
I don't but 100psi should be enough to start the system up.
I replaced the condenser in our van about 3 years ago, bought a set of gauges and pump of ebay, some gas (not r134, probably propane or something) from a local shop, a bit of oil and re-filled the van system, I didn't adhere to any weights or measures when I refilled it, just put in what I thought was robably about right and it still works perfectly 3 years later, in fact its the best/coldest aircon system I've used yet.
I replaced the condenser in our van about 3 years ago, bought a set of gauges and pump of ebay, some gas (not r134, probably propane or something) from a local shop, a bit of oil and re-filled the van system, I didn't adhere to any weights or measures when I refilled it, just put in what I thought was robably about right and it still works perfectly 3 years later, in fact its the best/coldest aircon system I've used yet.
I'm not sure about it at all to be fair, some things I've read state that its a PCM signal sent to the ECU in some vehicles, others say you can jump the connections but its all a bit vague and I don't want to fry the ECU, especially as I'm just doing a favour.
Its not worth spending too much money on it either, he is getting rid in six months max and getting something new. He is just winging at the minute because its so hot outside.
This is a new switch and it says its a NRF switch and I think they work as a signal rather than on/off.
https://www.ebay.co.uk/itm/192949348630?fits=Plat_...
Its not worth spending too much money on it either, he is getting rid in six months max and getting something new. He is just winging at the minute because its so hot outside.
This is a new switch and it says its a NRF switch and I think they work as a signal rather than on/off.
https://www.ebay.co.uk/itm/192949348630?fits=Plat_...
Right I've finally found time to have a look at this today. If you press the AC button nothing happens and about 5 seconds later the AC light on the buttons starts flashing. If you unplug the pressure sensor and press the button still nothing happens but the light stays steady like it should do.
The sensor has 3 wires to it, one is definitely ground (0V) and the other two have 5 volts each when the ignition is switched on, I've tried it with both connected to ground one at a time, both together and both to each other as well as all three together and it makes no difference what so ever, the compressor still wont engage.
If you meter the wires there are 5V on both rails but if you ground either one of them the voltage drops to zero and stays there until the ignition is switched off and back on, its like a short circuit protection has kicked in, I do think they need some kind of resistance between them and not just shorting to ground or each other.
Finally if I power the compressor directly from the battery it kicks in and the aircon works, the pressure is fine according to my gauges and the compressor works fine as well so it can only be a sensor can't it? I don't mind replacing the pressure sensor, a new one is £30 but I presume it would need re-gassing, I dont think the sensor is sat in front of a Schrader valve. I can re-gas it myself but it will be another £50 or so for the gas, also my mate has gone all greenie woke and wants the gas removing professionally.
The sensor has 3 wires to it, one is definitely ground (0V) and the other two have 5 volts each when the ignition is switched on, I've tried it with both connected to ground one at a time, both together and both to each other as well as all three together and it makes no difference what so ever, the compressor still wont engage.
If you meter the wires there are 5V on both rails but if you ground either one of them the voltage drops to zero and stays there until the ignition is switched off and back on, its like a short circuit protection has kicked in, I do think they need some kind of resistance between them and not just shorting to ground or each other.
Finally if I power the compressor directly from the battery it kicks in and the aircon works, the pressure is fine according to my gauges and the compressor works fine as well so it can only be a sensor can't it? I don't mind replacing the pressure sensor, a new one is £30 but I presume it would need re-gassing, I dont think the sensor is sat in front of a Schrader valve. I can re-gas it myself but it will be another £50 or so for the gas, also my mate has gone all greenie woke and wants the gas removing professionally.
stevemcs said:
Why don't you just pay someone to remove the gas, pressure test it and put the right amount in?
The gas isn't an issue, its bang on where it should be on my aircon gauges and its exactly the same pressure it was when we tested it 2 months ago, its definitely an electrical problem somewhere, I just want to be pretty sure its the pressure sensor before we remove it. If you put it on star you’ll definitely see a fault now as you’ve grounded the 5v supply!
You need to clear any faults then look at what the sensor is reading. Don’t go shorting 5v to ground - there’s a chance of permanently breaking something.
Look on Facebook and see if anyone local has a star or similar to read codes for you.
You need to clear any faults then look at what the sensor is reading. Don’t go shorting 5v to ground - there’s a chance of permanently breaking something.
Look on Facebook and see if anyone local has a star or similar to read codes for you.
LordLoveLength said:
If you put it on star you’ll definitely see a fault now as you’ve grounded the 5v supply!
You need to clear any faults then look at what the sensor is reading. Don’t go shorting 5v to ground - there’s a chance of permanently breaking something.
Look on Facebook and see if anyone local has a star or similar to read codes for you.
I said this in the first post but a couple of people suggested it would be a straight on off switch. The 5V does come back once its reset though, it must have some sort of protection build in in case the wires get damaged and short together I would have thought.You need to clear any faults then look at what the sensor is reading. Don’t go shorting 5v to ground - there’s a chance of permanently breaking something.
Look on Facebook and see if anyone local has a star or similar to read codes for you.
Its finding the time to sort it out to go on star though, we actually know someone who said they will do it for us but we are both so busy at the moment, I only got chance to look at it yesterday because a lazy customer wouldn't get out of bed.
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