Clicking AC low pressure switch

[Bitsyncmaster]

Yesterday I was driving in the morning with the AC running on blower speed 2. It was only about 75 degrees outside but it was sunny. The AC low pressure switch was clicking about every five seconds. I checked the vent temp and it was at 44 degrees so I don't think the AC needs a charge. It's just with that low blower speed and outside air not very hot the AC has very little effort to cool the air.

I don't think I will try to make a solid state low pressure switch but may try to wrap the existing low pressure switch with some foam to see if it would switch with less sound.

I don't think the clicking noise was the AC compressor clutch but I'm sure that was also turning on and off.

[FABombjoy]

If you're looking for new project, GPD 1711653 threads on to the low pressure port.

Depending on the quality of welds at the valve you may have to shorten the sensor port a few mm.

72182

[82DMC12]

I don't see how you can hear the low pressure switch changing state but you can certainly hear the A/C compressor relay clicking and the fan relay clicking during the conditions described. It's normal for the A/C to cycle every few seconds when there isn't very much load due to low ambient temp, and low demand. It doesn't necessarily mean the charge is low.

It probably does mean the charge is low if the doors are open, fan on high, A/C on, and it's 95 degrees outside though.

[Bitsyncmaster]

I don't see how you can hear the low pressure switch changing state but you can certainly hear the A/C compressor relay clicking and the fan relay clicking during the conditions described. It's normal for the A/C to cycle every few seconds when there isn't very much load due to low ambient temp, and low demand. It doesn't necessarily mean the charge is low.

It probably does mean the charge is low if the doors are open, fan on high, A/C on, and it's 95 degrees outside though.

My fan relay does not click (solid state). I really don't hear the compressor clutch click on and off. If you were to design a solid state low pressure switch the sensor would need to be able to accept 400 PSI just to be safe. So you probably would not have much resolution in the 20 to 30 PSI range.

[FABombjoy]

If you were to design a solid state low pressure switch the sensor would need to be able to accept 400 PSI just to be safe.
I'm doing exactly this, ECU controlled low pressure cycling.

Struggling to imagine a situation where the low pressure side needs a 400psi safety margin.

[Bitsyncmaster]

I'm doing exactly this, ECU controlled low pressure cycling.

Struggling to imagine a situation where the low pressure side needs a 400psi safety margin.

When your parked on pavement in the hot summer sun, I bet your AC system is around +120 degrees/F. Static pressure of R134a at 120 deg/F would be 171 PSI. Now could it get hotter, I don't know. At 150 deg/F it would be 263 PSI.

[FABombjoy]

I don't think you need 400PSI rated resolution to get a switch that holds up at 400PSI.
Like a 1 bar MAP sensor doesn't become a pressure relief valve at 2 bar.

The part I posted is designed for automotive AC systems. I have no concerns.

[Bitsyncmaster]

I don't think you need 400PSI rated resolution to get a switch that holds up at 400PSI.
Like a 1 bar MAP sensor doesn't become a pressure relief valve at 2 bar.

The part I posted is designed for automotive AC systems. I have no concerns.

I tried to get a data sheet for that part you posted and did not find one. GPD 1711653 I'm not even sure it is a sender or just a switch.

[FABombjoy]

I tried to get a data sheet for that part you posted and did not find one. GPD 1711653 I'm not even sure it is a sender or just a switch.
It is a high pressure transducer. This should tell you everything you need to know.

https://lemon-manuals.la/Audi/2014/Q7%20TDI%20Premium/Repair%20and%20Diagnosis/Heating%2C%20Ventilation%20%26%20A%2FC%20%28HVAC%2 9/HVAC%20Control%20Systems/Heating%2C%20Ventilation%20%26%20Air%20Conditionin g/87%20Air%20Conditioning/Diagnosis%20And%20Testing/High%20Pressure%20Sensor%20G65%2C%20Checking%20Pre ssure%20Signal/

I don't yet know how well it will respond at lower pressures, but it will be easy to swap-on and take readings.

[Bitsyncmaster]

It is a high pressure transducer. This should tell you everything you need to know.

https://lemon-manuals.la/Audi/2014/Q7%20TDI%20Premium/Repair%20and%20Diagnosis/Heating%2C%20Ventilation%20%26%20A%2FC%20%28HVAC%2 9/HVAC%20Control%20Systems/Heating%2C%20Ventilation%20%26%20Air%20Conditionin g/87%20Air%20Conditioning/Diagnosis%20And%20Testing/High%20Pressure%20Sensor%20G65%2C%20Checking%20Pre ssure%20Signal/

I don't yet know how well it will respond at lower pressures, but it will be easy to swap-on and take readings.

That looks like a high pressure sensor. I think the graph is showing BAR. So it looks like it will be safe but not sure it responds to less than 1.8 BAR (26 PSI).

[DMC-Ron]

That looks like a high pressure sensor. I think the graph is showing BAR. So it looks like it will be safe but not sure it responds to less than 1.8 BAR (26 PSI).

Right. The duty cycle square wave gets stable at above 2 bar (29 psi). If you were using R134a this would be 34 degF, or 31 degF for R12. Seems like that could be workable?
Ron

[FABombjoy]

The chart shows the acceptable operating range for climatronic, not the sensor itself. It produces a stable D/C at atmospheric pressure.