Chris' BX blog

Tell us about life with your BX, or indeed life in general!
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white exec
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Re: Chris' BX blog

Post by white exec »

Can anyone help confirm my hunch about an A/C resurrection snag...?

- new Nissens (=Sanden SD709) compressor, pre-loaded with PAG46
- new O-rings throughout, except for TXV (not so far removed)
- new dryer
- new pressostat
- system regassed, 680cc R134a (85% of OE 800cc of R12)
- no leaks now showing (held vac down to 1mbar for 4mins)

But
Compressor (and rad fans) correctly operate when AC selected, but NO COOLING.
After a few minutes of idle-speed running, with compressor remaining on all the time, still no cooling, or any temperature rise on the HP output union/pipe from comp to condenser. Would expect to feel this pipe/hose get warm.
After 5 mins running, compressor body has got appreciably hot, but no noticeable temp rise of the HP output pipe/hose.
Still no cooling delivered.

My guess is that the TXV is blocked (blocked shut), so no refrigerant entering the evaporator.
The 3-way pressostat is allowing comp to run, so dryer (HP) is neither under- or over-pressure, which seems a good sign.

Reckoning my next move should be to replace the TXV.
Does that seem sensible?

Any tips on removing it, in this case for LHD?
Chris

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Re: Chris' BX blog

Post by xantia_v6 »

Were any pressure readings taken while the engine was running?
It is also possible that it is a faulty compressor which is not actually pumping. Can you turn the compressor by hand and feel the compression strokes?

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Jaba
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Re: Chris' BX blog

Post by Jaba »

Yes sounds like no circulation hence no cooling. TX valve does get blocked as the metering of the R134 is very fine. Easy enough to get it depressurised and whip it off for cleaning with brake cleaner. It may of course be faulty and stuck closed. You will have to undo that too tight bulkhead union as I dont think the TX valve comes out with that still connected. I assume you have factory fit A/C.
One thing that is sub optimal about the BX a/c is that there is only a charging valve on the high side. This means that the vacuum cannot be tested at the compressor which it is sometimes desirable to help in fault diagnosis like yours.
I was going to get a second charging valve fitted in mine a few years back, the guy ordered the valve for me but before I could get it done the car went off the road for head repairs, had a respray and then covid struck.......
The Joy of BX with just one Citroën BX to my name now. Will I sing Bye Bye to my GTI or will it be Till death us do part.

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white exec
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Joined: Sat Sep 12, 2020 4:04 pm
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- LHD, NA, AC, RP_5800
1996 XM 2.5TD Exclusive
2003 Toyota RAV4 2.0 D4D
x 46

Re: Chris' BX blog

Post by white exec »

Thanks both for coming back on this - really appreciated.

Mike, I will try tomorrow turning the comp by hand (probably with a brace-wrench) to see what the resistance is like. My guess is that it is pumping, as the engine rpm drops very slightly (and recovers within a second or two) when the AC is turned on.

One charging valve is a pain, although there didn't seem a problem with working with just the one this morning for an evac and fill. Mike, I don't have any test figures for pressures. The mechanic this morning only remarked that the blue gauge on the machine remained higher than normal, I think after the engine was shut off. I think he was saying that he expected this reading to fall. You might be able to interpret that.

Jaba, I'll remove and replace the TXV. It was all factory original, 29 years old now, and last used heaven knows when - the AC was not seemingly gassed when I bought the car last October, although the system was all there, and reasonably clean oil still in the comp.

I'm a bit short on removal procedure for the TXV, so have a few QQ...
The two bulkhead hoses obviously have to come off.
Then a rubber surround for the 'oval' plate?
What secures the TX valve body to the evaporator? and it this accessible from the engine bay, or is it a footwell job?
There seem to be two? or four? O-rings, in addition to the two for the hoses.

You've obviously done this job before, so advanced advice welcome.

Hoping that another vac-out and re-gas (have had two already!) will be the last, as at €70 a throw, pretty much the going rate here now.

One last question:
When evacuating - via the only (HP) fill-valve, which is low down, and right next to the comp D port - is there any danger of compressor oil being inadvertantly removed? I was guessing that with later systems, where the (two) fill valves tend to be at the top of the system, the compressor's stock of oil would be left intact.
I noted that the mechanic had set the machine to deliver only 10cc of fresh oil, presumably because the comp was brand new and pre-filled.
Chris

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Jaba
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Re: Chris' BX blog

Post by Jaba »

They can store the extracted gas and save it for later usually. TXV unions are a similar size to the bulkhead ones. It attaches to the evaporator with more unions all accessed from the footwell after removing the small side cover. New orings essential I would say.
See what the needle valve is blocked with and if it isn't and you can blow through it then there is not a blockage there.

It costs 60 or 70 GBP here too the gas has gone up a lot I am told but be grateful as the new gas R1234???xxx is charged at twice that.
The Joy of BX with just one Citroën BX to my name now. Will I sing Bye Bye to my GTI or will it be Till death us do part.

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white exec
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2003 Toyota RAV4 2.0 D4D
x 46

Re: Chris' BX blog

Post by white exec »

Lovely, thanks for confirming how the TXV is attached. Footwell, LHD - looking forward to that!

It was the inadvertant removal of oil that I was wondering about, due to the low positioning of the fill/evac point, so close to the compressor. Could oil be sucked out?

One other thing I'm unclear about...

Converter valves for R12 to R134a:
I am using these:
https://www.amazon.co.uk/gp/product/B08 ... UTF8&psc=1

The dark red one is marked H, and has an 8mm female thread, and a smaller quick-fit end.
The blue one is marked L, has a 10mm female thread, and a larger q-f end.

Only the blue one will fit the male thread on the BX's fill point.
But this is the HP side, surely.
Does this matter for garage use of this filling point, as it seems to be swapped around?
Chris

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Re: Chris' BX blog

Post by Jaba »

I would not worry about the oil as they seem to have away of seeing how much oil is present and needed when refilling.
Just use the charging valve that fits onto the schrader valve. You did take the valve core out first? The colour coding only matters when there are two valves. They can charge through either so no big deal if there is only one to choose.
The Joy of BX with just one Citroën BX to my name now. Will I sing Bye Bye to my GTI or will it be Till death us do part.

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white exec
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Posts: 380
Joined: Sat Sep 12, 2020 4:04 pm
Location: Sayalonga, Malaga
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- LHD, NA, AC, RP_5800
1996 XM 2.5TD Exclusive
2003 Toyota RAV4 2.0 D4D
x 46

Re: Chris' BX blog

Post by white exec »

Reassuring, so thanks. I did remove the original schrader.
Chris

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white exec
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Posts: 380
Joined: Sat Sep 12, 2020 4:04 pm
Location: Sayalonga, Malaga
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- LHD, NA, AC, RP_5800
1996 XM 2.5TD Exclusive
2003 Toyota RAV4 2.0 D4D
x 46

Re: Chris' BX blog

Post by white exec »

A good Schoolday today, with some detail I found useful about the Thermal Expansion Valve (TXV) on the BX.

Have had the system evacuated (again) so I can replace the TXV with a new one, when it arrives next week.
Evacuation emptied both the gas and the oil from the system, both to be replaced when the new TXV is on.
Valve ordered from Mister Auto: a Mahle AVE 87 000P.

I found this PowerPoint presentation a really clear explanation about the types of TXV in use, how they work, and symptoms of a misbehaving one:
https://www.macsw.org/WEB/images/Macs_D ... TS/TXV.pdf
It's by Parker—Four Seasons—Standard Motor Products.

The TXV on the BX (OE pt.no. 6461 J3, NFP) is the 4-port (threaded) type, hence the reference on the forum to its 4 O-rings.
Reassuring to know in advance what I should find attached to the heater evaporator... :?

Must say thanks to everyone who has helped with advice on this one. It's just not an area (of any car) that I've had experience re-building.

Should know more later next week.
Chris

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white exec
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Joined: Sat Sep 12, 2020 4:04 pm
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- LHD, NA, AC, RP_5800
1996 XM 2.5TD Exclusive
2003 Toyota RAV4 2.0 D4D
x 46

Re: Chris' BX blog

Post by white exec »

Towbar
Towbar now wired up, and while I was at it put together a 12N test board, with a lead long enough to sit it near the driver's door.
Been wanting to knock together one of these for aeons, so finding some trailer light fittings for just €6 each did it.

New BX towbars not easy to find, so was pleased to discover this company in Malaga. A local agent of theirs fitted it (professional and certificated fitting obligatory here).
https://www.lafuente.eu/towbars/citroen/bx/car/1992
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Chris