Xantia A/C not working at idle

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BalloonFish
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Xantia A/C not working at idle

Post by BalloonFish » 15 Mar 2017, 16:15

Hello; I'm hoping someone here can shed light on my A/C problem which has me a bit stumped.

I bought the Xantia last summer and the A/C worked fine, although it probably wasn't blowing as cold as it could/should. During the winter it seemed to stop working in the sense that I wasn't getting cool/dry air - the rad fans, blower, distribution slider, recirc/fresh slider and cabin temperature sensor all worked fine.

A few days ago I took the Citroen to a local garage (a good one but not a Citroen specialist) and asked them to regass the system. They were unable to get the compressor to run and so couldn't do a full system flush/regas. They fitted a new LP/HP switch but to no avail.

After looking around some threads I've had a little go at some diagnosis. By bridging the two centre contacts in the pressure switch plug I can get the compressor to kick in but ONLY when the engine is running (even if the ignition is on the engine has to be running). Since the cooling fans also only run when the engine does I'm assuming the entire A/C system has a cut-out so that it stops when the engine does; this makes perfect sense - I'm guessing it maybe piggy-backs the RPM sender or the alternator output?

Anyway, with the engine running I can make the compressor engage with the engine at idle (or any other speed, come to that) by bridging the switch contacts and the A/C system blows cold. But with the pressure switch plugged back in I found that the compressor ran quite happily when the engine was carrying some RPM. The instant the revs drop to idle (800 rpm with a warm engine) the compressor clutch kicks out so no A/C, although the cooling fans continue to run. Pick the revs up to above 1200 or so and the compressor will run as it should. With the revs at between 900 and 1200 the compressor will engage, almost instantly de-clutch and then try and run again a few seconds later.

So as long as I'm driving along in a normal fashion the A/C works. At engine idle it doesn't. I have a few hunches but only having learnt pretty much all I know about air con systems from reading this forum for the past couple of days I have no idea if they're any good;

1) That the system is low on gas (so it's getting an LP cut-out at low RPM) so it needs to be regassed again with the revs being held up a bit to allow the compressor to run to fill the system properly.

2) That the compressor is worn and can't maintain proper system pressure at low RPM.

3) That there's a bad electrical connection or similar causing a voltage drop so the compressor clutch can only stay in when the alternator is really putting out a good charge.

Other information that might help people:

- We're talking about a Mk1 Xantia TD with the Bosch pump, all mechanical. It's got the waxstat cold start mechanism (which doesn't work) but there's no vacuum/electronic cold-start system which, if I understand correctly, also raises the RPM on the later cars when running the A/C.

- Everything else to do with the heating/vent system works fine; all the blower speeds work and the 'Auto' setting changes the fan speed and output temperature as required by the temperature slider (and the weather), whether the A/C is switched on or off and whether the compressor is actually running or not.

- Both cooling fans come on as they should (at half speed when the A/C is switched on). Unplugging the sensor from the thermostat housing causes them to run at high speed so I'm guessing the Bitron unit is fine.

- As long as the engine RPMs stay up the A/C produces pretty cool air and it demists well.

- The sight glass on the drier (?) is clear and empty when the system isn't running. When the compressor kicks in it almost instantly fills with green fluid (with the odd bubble in it for the first few seconds). Once you switch the system off you can see the fluid drain down over the space of about 5 seconds.

Thanks in advance; it's a bit of a 'wall-o-text' but I've tried to include as much relevant info as I can think of.
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Re: Xantia A/C not working at idle

Post by white exec » 15 Mar 2017, 17:11

Hi BalloonFish, and welcome to the Forum.

That's a clear and detailed description of the problem.

There's a good bit of Citroen service information on the Xantia AC system here (see p.282 onwards; index up front):
http://www.peli59.net/xantiafaq/XANTIA_XM_EVASION_2001.pdf

The system is designed not to operate if there is insufficient gas in the unit, to prevent damage. Check that it has been recharged to the correct weight, along with AC oil.

I'm sure someone will be able to post an appropriate Xantia electrical diagram of the AC/heating system, if needed.
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Chris