3B Aircon Pressure

[Tonks4x4]

I have a quick question about the gas pressure on my aircon system. The clutch was not pulling in on my aircon compressor, I have traced it down to the fact that the Low Pressure Switch is not allowing the aircon unit to trigger. Once the switch is bypassed everything appears to work. I have changed the switch but it still does work. I had it regassed tonight but just need to know what pressure should be in the system to operate the switch.

ta in advance....

[4WheelDrifter]

What colour is the switch housing?

[johne]

Around 3 bar, 45 psi.

Don't bypass the low pressure switch for long, it's crucial to the operation of the aircon. If it's not closing it means there's not enough R134a in your system and remember the compressor is inhibited at temperatures below approx. 4 degree C.

John

[rj scotty]

Don't know the pressure as it is very temperature dependent your probably looking at a high and low acceptable figure. I believe the system needs about 8KG of refrigerant/oil.

Jonhe will be along shortly, our resident A/C expert

[rj scotty]

Beat Me too it

Hello Johne

And yes nobody's compressor will be kicking in at the moment

[4WheelDrifter]

I've got:
Opens - 1.45-1.6 bar
Closes - 2.9-3.2 bar.

[johne]

Don't know the pressure as it is very temperature dependent your probably looking at a high and low acceptable figure. I believe the system needs about 8KG of refrigerant/oil.

Jonhe will be along shortly, our resident A/C expert

8Kg!!! no wonder everyone complains the A/C weighs so much! It's actually around 1.3Kg, 3 tins iirc. I need to look the exact amount up.


John

[rj scotty]

Could have made that up just something I remember the guy who filled mine telling me, 8 something or other.

[4WheelDrifter]

Again I've got the 3B as having 1050g + 20g of R12. Not sure on the R134a though.

[s2driveruk]

think its 750g for R134a but cant be sure

[s2driveruk]

http://www.s2forum.com/forum/showthr...ghlight=aircon post 7 lists the gas fills

[4WheelDrifter]

Audiman knows, and my air-con always worked really well, so that is good enough for me.

[rj scotty]

think its 750g for R134a but cant be sure

perhaps it was 800g then. Oh well I was only 10X out

[Tonks4x4]

Around 3 bar, 45 psi.

remember the compressor is inhibited at temperatures below approx. 4 degree C.

John

Thanks for that, is it 45psi with the pump running or stationary?
Where does it read the 4 degrees from? It was in a heated garage approximately 20 degrees.

[johne]

Thanks for that, is it 45psi with the pump running or stationary?
Where does it read the 4 degrees from? It was in a heated garage approximately 20 degrees.

You need more than 3 bar pressure without the compressor running. That way, when you demand A/C the low pressure switch is closed and the compressor can energise. As the system cools down the pressure on the low side will fall and as it reaches 1.5 bar the low pressure switch opens causing the compressor to drop out allowing the system to warm up, pressure to rise back to 3 bar and the whole cycle starts again.

The "4 degrees" is read at the air intake just underneath the pollen filter and before the fan. On manual A/C cars it's a straight thermal switch that opens around 4 degrees cutting off the supply to the A/C relay. On climate controlled cars it's a NTC thermistor that the Climate Control Unit reads (along with the one in front of the radiator) to determine the outside temperature and stop the compressor activating.

John