Diagnosing AC issue

[MajorJack]

Hi guys,

I've recently taken over my grandfathers Peugeot 406, built in 2003 (Modell number 3003/894, 2.2 liter gasoline engine, 158 hp)
The AC isn't working and while I had the car at the workshop for changing the main engine belt, they also refilled the AC and checked it for leaks (no leaks found). However they told me that it doesn't build up enough pressure to cool anything.
Since I needed the car for going to work on the next day, I couldn't have them look into it any further than that.

When I turn on the AC switch in the cockpit, a metallic clunk can be heard in the engine compartment and the engine's rpm go up a little, just as it should be. However, as previously stated, the AC doesn't build up enough pressure and doesn't cool the incoming air down at all (at least not that I could feel any difference).

So I know failure of the AC relay is a common culprit with the 406 and I know about the repair instructions for the Siemens BSI found in the older models.
However, my car has the VALEO BSI and I couldn't find anything on the internet about how to identify a broken AC relay on the VALEO BSIs.

So I'm looking for advice on diagnosing the issue and

• wiring diagrams of the Valeo BSI

• information about the location of the AC relay on the Valeo BSI

• information about the location of the AC compressor in the engine compartment

• other ideas what the issue might be

any help would be greatly appreciated!

[steve_earwig]

The compressor is the lowest gadget (AFAIR) on the drive belt end of the engine. I've never found anything that shows the inside of the later BSI, I don't think they go wrong on those - probably famous last words but I don't think it would even try to engage if the relay was broken. I'd post a wiring diagram but it's telling me to reinstall it again It probably won't show you much of any use anyway.

Could the compressor have died?

[MajorJack]

Well I've checked the magnetic clutch, the relay triggers that just fine in the cockpit and that's the metallic sound,
so yea I guess the next likely culprit is the compressor. How can that thing not function though if it is turned by the drive belt?

[steve_earwig]

I presume they wear out eventually. Not much idea really, usually they don't work because they don't have enough gas, a sensor goes up the swanny or the clutch fails, all of which mean the clutch isn't engaged.

a metallic clunk can be heard in the engine compartment and the engine's rpm go up a little

I can't remember my D9's engine revs going up a little, I suspect the ecu just raises the fuel to compensate and the revs should stay the same. Unless it's preset and it's compensating for drag that isn't actually happening. I did notice on my D8 that if I held it above idle using the throttle engaging and disengaging the air con made a noticeable difference.

[Welly]

If the compressor 'clutch' definitely 'clicks' then and the inner part of the compressor pulley rotates then the compressor is working.....hold the larger of the 2 aluminium a/c pipes (the low pressure one) and you should feel cooling going on.

The fact that cool air is not being delivered in the cabin could be a blocked Pollen Filter (located behind the windscreen scuttle panel) .....or....the a/c has been over-gassed and the evaporator is freezing over (blocking air flow) .....or..... the expansion valve filter mesh is blocked (debris in system) but this normally only follows compressor failure......or..... the desiccant drier is saturated causing ice to form inside the a/c piping (too much moisture).

Once you have established the compressor is ok and there's no obvious leaks then I'd recommend using a specialist a/c company to properly vacuum the system, pressure test with Nitrogen, re-gas, and add the correct oil to the refrigerant.

[PhillipM]

The clunk should be the clutch engaging, you should be able to see the centre of the pulley engage if the clutch is working properly if you get someone else to hit the button while you watch, check that first.

It's not unknown for the insides of the compressor to seize though - mine did the same thing - and a while before that I had the clutch not engaging well enough to drive it as the plates had all rusted from not being used as the car wasn't gassed up when I got it. Cleaning the clutch is an easy job, rebuilding the compressor isn't though, swapping it is far easier.

[MajorJack]

Thanks for your replies!

I've just turned on the engine and then the AC, the metallic clunk is indeed the clutch starting up, turns on and off just fine, i.e. I can see the clutch spinning on the compressor.
However the compressor doesn't seem to work at all, both pipes coming out of it didn't change temperature at all and remained warm to my hand even after the car had run for 5+ minutes (it's been fairly hot today).

Actually the car has been standing for months before I picked it up from my granddad, he wasn't physically able to drive anymore. I picked it up in mid February and when I had the AC refilled in April, it was like 2/3rds empty. The AC never worked since the car has come into my possession.
So rust on the plates of the clutch doesn't seem unlikely or the compressor may have failed altogether.

What should I do next? Is there a way I can further pinpoint the issue?
And how big of a mechanical challenge is cleaning the clutch or replacing the compressor?

[WillNZ]

If the compressor is latching and spinning up then it will not be too short of gas. As you say you cant feel any difference in temp across the high/low pressure lines at the compressor, this suggests there is a blockage somewhere. Get someone knowledgeable to couple it up to a set of gauges, this will tell you exactly what gas pressures you have and whether the gas is flowing properly or not.