AC diagnosis help - Golf Mk 4

[25th QV]

Further to my 'where to get R134a' thread, I've started to diagnose my system, or at least try to, but I'm running out of ideas.

2004 GTTDI 130 ASZ with Climatronic.

Symptom - AC compressor does not activate, hence AC does not work.

Checked the main fuses which appear to be intact snd gave them all a wobble, just in case.



Hooked up my manifold gauges....



Set the system to AC off....



And observed these readings...



Then set the AC on full....



And observed these readings....



My initial observations are that 1) There is a reduction in pressure on the low side when the system is turned on (why, if the compressor is not running) and no change in the high side (which makes sense if the compressor is not running, but where is the low side pressure going?

Next question I ask myself is why is there a difference in pressure between high and low when the system is not running - should be the same, surely?

Welcome thoughts and next diagnosis steps.

Thanks in advance.

[25th QV]

Just to add, having found this:

http://www.saunalahti.fi/~jues/Climatronic_Self_Di...

My climatronic shows the following two codes:

0318 Air Conditioner Pressure Switch 0x23

04FA - Recirculation Flap Servo Motor 0x253

Would I be correct in assuming the recirculation code is a red herring to the AC not functioning and that the smoking gun is the pressure switch?

Or if the system pressure was low, would that show as a switch fault?

Not sure if my pressure readings are in spec or not?

[The Road Crew]

Pressures are near enough with compressor off

As you've a pressure switch fault it could well be this giving a false signal, which doesn't allow the compressor to engage (effectively protecting itself from running)

Investigate the signal to/from the pressure switch...

[25th QV]

Cheers, any idea on how to test or bypass the switch?

[The Road Crew]

3 pin is it?

5v ref
Ouput
Ground

5 mins with a multimeter should give you some indication.

As you have a set of pressure gauges I presume you have a multimeter!

[autohead]

You might have the pressure but not volume of gas required. The first step would be getting the gas removed to see how mach is in the system.

On a diag reader you should be able to read values from the AC pressure sensor to aid diagnosis

[autohead]

You could also check the compressor is getting the 12v switch voltage to turn on/off before removing the gas.

[Demelitia]

The comment above about the pressure switch code causing the system to not engage is probably the most solid guess.

If possible, it will also be worth trying a known-good faceplate for the climatronic.
I’ve seen quite a few instances of problems with the hvac system being caused by a failure of the faceplate itself, rather than the codes being correct.
This is on b5.5 Passat’s of the same era so take this with a pinch of salt.

Have you tried deleting the codes from the climatronic? You may get some different behaviour from it when the codes aren’t there which might help you with your diagnosis.

The comment above about the pressure switch code causing the system to not engage is probably

Edited by Demelitia on Monday 10th January 13:07

[25th QV]

Thanks all.

The pressure switch cannot be read from a multi-meter, only a scope due to it's function type (so I've read), which sadly I don't have, nor a scanning tool beyond the climatronic self diagnostic codes.

Any idea how I delete the codes from the face plate to see if that makes a difference?

Can I check how I put 12V to the compressor to test clutch engagement - assuming I'm using my jump pack and croc clips here to add 12V - exactly what to I put where? (Electrics aren't my strength, beyond the basics)

Wasn't aware the system could measure or sense the volume of gas as well as the pressure?

[Demelitia]

Press and hold econ for 2 seconds after the last error code is displayed. Page 1 of the pdf mentions it.

[The Road Crew]

25th QV said:

Thanks all.

The pressure switch cannot be read from a multi-meter, only a scope due to it's function type (so I've read), which sadly I don't have, nor a scanning tool beyond the climatronic self diagnostic codes.

Any idea how I delete the codes from the face plate to see if that makes a difference?

Can I check how I put 12V to the compressor to test clutch engagement - assuming I'm using my jump pack and croc clips here to add 12V - exactly what to I put where? (Electrics aren't my strength, beyond the basics)

Wasn't aware the system could measure or sense the volume of gas as well as the pressure?

Is it a 3 pin switch? On that age of car everything isn't fibre/can/lin bus so I'd be interested to read why you cant read the voltage going to /from it.
Got to be worth a try hasn't it?
Find it how many pins in the switch, look up a wiring diagram, probe the individual wires - might be as simple as a broken ground wire in the loom, or a corroded connector/pins.

I'm not aware it can measure both volume and pressure, not saying it cant but it seems odd. Surely it's sensing pressure in the pipe it's located in?

Surely the pressure comes from the volume of the gas? If you've a very small amount of ac gas in the system then the pressure will be very low. Put more (pressurised) gas in then the pressure increases?

[25th QV]

The Road Crew said:

Is it a 3 pin switch? On that age of car everything isn't fibre/can/lin bus so I'd be interested to read why you cant read the voltage going to /from it.
Got to be worth a try hasn't it?
Find it how many pins in the switch, look up a wiring diagram, probe the individual wires - might be as simple as a broken ground wire in the loom, or a corroded connector/pins.

I'm not aware it can measure both volume and pressure, not saying it cant but it seems odd. Surely it's sensing pressure in the pipe it's located in?

Surely the pressure comes from the volume of the gas? If you've a very small amount of ac gas in the system then the pressure will be very low. Put more (pressurised) gas in then the pressure increases?

The switch on these produces a square-wave output with duty cycle depending on the pressure, hence needs a scope to read (so I've read on a few forums). The switch is buried on the rear firewall under the scuttle behind all sorts and almost impossible to reach without a bit of a strip down - car is in daily service so will have to look again at the weekend.

[stevemcs]

Have you actually checked to see how much gas is in the system ?

[E-bmw]

I would say that assuming those gauges were plugged in when the system is static then the pressure is too low.

IIRC around 90psi is an average static reading, then when the AC is running more like 30/200 low/high, but I may be remembering that incorrectly, I am sure someone will confirm this or not.

[25th QV]

stevemcs said:

Have you actually checked to see how much gas is in the system ?

Only using the manifold gauges to check pressure - I'm not aware of a way to differentiate pressure versus gas content without evacuating the system which I'm not equipped to do.

[25th QV]

E-bmw said:

I would say that assuming those gauges were plugged in when the system is static then the pressure is too low.

IIRC around 90psi is an average static reading, then when the AC is running more like 30/200 low/high, but I may be remembering that incorrectly, I am sure someone will confirm this or not.

Thanks, I'll need to research what the static pressure should be as post number three suggests there or thereabouts.

It's been this way for 3 years now so I have to assume if there was a leak, pressure would be zero now?

[stevemcs]

25th QV said:

Only using the manifold gauges to check pressure - I'm not aware of a way to differentiate pressure versus gas content without evacuating the system which I'm not equipped to do.

Start with getting the gas levels checked then go from there

[25th QV]

stevemcs said:

Start with getting the gas levels checked then go from there

How are gas levels checked other than by draining the system and weighing what comes out?

I was under the assumption that gas levels and system pressure were inter-related?

[E-bmw]

25th QV said:

stevemcs said:

Start with getting the gas levels checked then go from there

How are gas levels checked other than by draining the system and weighing what comes out?

Yes, that is right.

1. Evacuate system & measure gas.

2. Check for leaks.

3. Refill with correct amount of gas.

4. Test system.

[The Road Crew]

50 psi about right on a cold winters day.
90psi about right on a warm summers day.

Temperature affects pressure a lot (obviously I hope!)

https://ricksfreeautorepairadvice.com/static-press... Plenty of other info online, just the first i found.

High and low pressure should be equal with engine off (after half hour or so) - this shows you've no blockages.

Pressure on both sides at 50 in winter says to me your gas level is about right. Certainly enough for the compressor to engage to do further diagnosis.

If you had no gas, you'd have no pressure would you? Cos where is that pressure from otherwise?

If your gas was very low, your pressure would be low (/empty)

If your gas level was too high, your pressure would be too high. Remember to compesate for ambient temperature when making any comparisons.


OP - assess serviceability of your pressure switch and the cooling fans...failure in either area will trip the compressor and prevent it starting.