Chris' BX blog

[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?

[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?

[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.......

[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.

[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.

[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?

[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.

[white exec]

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

[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.

[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
.

DSCF3912.JPG

DSCF3913.JPG

[white exec]

Air-con
Good news today - new expansion valve finally fitted, and the system pressure tested and re-gassed (again) this morning.

It works, and can freeze socks off...

A separate write-up of this LHD TXV fitting has been done:
viewtopic.php?p=270638#p270638 .

[xantia_v6]

Congratulations Chris, Full marks for perseverance

Keep an eye on all of the pipework and joints for oily stains which would indicate a slow leak.

[white exec]

New towbar (and an accompanying 90 pages of technical and fitting certification) finally got inspected and signed off at the local vehicle test centre today. Another €86 for the privilege of having it included on the ficha tecnica for the car.

The inspection, at 0800 this morning was not without complication. To begin with, the office decided to pull the thick file, and start re-reading it, even though all the paperwork had already been approved. Then I pay for the inspection, to find that an emissions check has been included, running the bill up to €91. What?? Member of staff explains that it's now policy to run an emissions check on any vehicle submitted for a 'non-periodic' test, alongside the main item. OK, so be it...

I wait outside for the car's reg.no. to appear on the big display, and which of the inspection lanes to go to. After half an hour, zilch, so back to the office and 'what's happening?'. Within seconds, we appear in green at the top of the list, and off to Lane 2 - the HGV one.

On the inspection lane, the technician looks at the paperwork and cannot understand why an emissions check has been stipulated, when all that is needed is the towbar check. He escorts me back to the office, where they explain nothing, but refund the €91 to my card. Then charge me €35 instead, which turns out to be wrong. This is immediately refunded, and the charge becomes €51.

Back on the lane, the technician is mid-way through the dummy tail-board test, when we're both called to the office again, and (without explanation, but several apologies) the €51 is refunded, only to become €86. (Those of you still following this - which didn't include myself - will spot that it was just the charge for emissions test that was knocked off.)

I jokingly offer to join the Station staff, as I'm spending so much time in the office now. Surprisingly, they take this in good humour.

Back on the line, car is finally over the pit, and the Inspection of The Bar commences. In much less than a minute, it's all over, and technician declares 'no problems'.

Back to the office, and a 40-minute wait while they overprint the car documentation with Modification/Addition details, including bar type, max tow weight and max ball loading. It took 40+ minutes because they get some of the details wrong. Twice. I now have three Mod/Add printed 3-line entries – the first two being overstamped in red "Anulado", but the final one with the all-important Green approval stamp. (The errors were in one digit in the legal conformance regulation reference, obviously important.)

So, a mere 1h40 there, but it's done. Legal, paperworked, homologated, and bloody expensive.

[white exec]

Still a bit of low-down metallic 'grundling' from the aux belt, although a good bit reduced by greasing the bearings on the main tensioner pulley.
,

BX AC belt part nos..jpg

I can find the swinging tensioner on Cit Parts (6453 C6), but can't find the upper jockey wheel, sometimes referred to as a 'diverter' pulley.
It's different from the small tensioner pulleys on non-AC and other models.

Can anyone help with its part no.?

[Jaba]

Yes thats an odd one. It is actually on the alternator long mounting bolt. Not all cars seem to have it or the one at the bottom. My GTi has neither but I think the alternator position is a bit higher than a diesel so maybe the belt does not need the extra wrap around to stop it slipping.