How Colds your Aircon

[kiwi]

Well for those of us that have it fitted that is

Today was one of those warm and muggy wet days where having Aircon was literally the best thing out that avoided getting wet either from and open sunroof, window or just simple humidity.

So out curiosity I placed a temperature probe against one of the airvents with the blower on full speed and aircon on

-16c

no wonder people find the aircon system of the BX so cold.

[Defender110]

ALTERNATE QUESTION:

How deep is your SNOW?

[Tim Leech]

Mines very cold, not that it works but its bleeding freezing!

[kiwi]

ALTERNATE QUESTION:

How deep is your SNOW?

Actually was asking a semi serious question which has intrigued me from another thread was reading about heater blowers.

But since you asked read this from our local weather forecast

Tomorrow
30 December
Issued at: 12:54pm 28 December 2009
Showers becoming less frequent, and confined to eastern and southern slopes. Snow lowering to 1800 metres at night. Gale westerlies tending southwest and easing from afternoon.
Free air freezing Level: Lowering to 2000 metres at night.

So back to the question what should be the temperature of the BX aircon system and how do you know its not working properly? Sometimes it just cuts out is that a sign of the need to regas?

Sorry you may struggle with the question being the opposite of seasons and apologies for not placing this in technical.

[demag]

-16C is incredible. I remember a post on FCF a few years back where everyone checked their a/c to see what it was. Mine was about 2 or 3 degrees I think and it was one of the best. (Pug 405 td).

[Vanny]

I'd be having words with your temperature probe supplier! If the atmospheric humidity is much more than 60% and your evap temp gets below -5c then you wont have any air blowing out of the vents, you'll have a block of ice in the way!

Ideal temp is around 3c to -5c. You might be able to get a little lower when on full recirc (less moisture).

What sort of probe is it, and where 'against' the vent did you place it? Against suggests you had the probe physically resting against something so are you simply measuring the materials surface temp? You don't mention which vent, was it centre, end of dash, defrost, foot?

I will make the assumption that your heater core was fully shut off and the AC had been on for some time (thus removing residual heat from the heater).

Either way it sounds like your refrigerant system works, which is good, and it sounds like your refrigerant level is about right (if it is LOW or HIGH then temps will warm up pretty quickly).

When you say it cuts out, how do you mean 'cuts out'? Does it simply warm up? Or does a light go out? Or have you an indicator that the compressor pump has switched out?

What should happen is that the system will get up to pressure (300psi ish) then start cycling the compressor clutch in and out in order to control the evaporator temperature. If the pressure becomes to great there is a switch in circuit to knock the compressor off. There is also a thermistor on the evaporator which should switch the temperature off if it goes below 5c.

It sounds like your thermistor might have failed (4k7 i think) probably through a damaged wire. This will mean the control module doesn't back the compressor off, the evap freezes and eventually the system goes over pressure (OP). The OP switch is mechanical so trips the compressor clutch and the temp rises (probably quite rapidly). If this is the case you can check the resistance of the thermistor quite easily (the connector is behind the radio) and then replace the thermistor for a couple of pence, and a days worth removing the dash and HVAC unit, replacing and putting back.

[demag]

Ha just looked on FCF and found it! As I say this was a 405td.

Posted: 23 Jun 2005 05:16 Post subject: Reply with quote Edit/Delete this post
Ok then,
Checked the temp at the dash outlets this evening whilst at work (well might as well get paid for doing it eh?) With fast fan and fresh air it was about 8c. On recirc with fast fan about 7c.
Recirc with slow fan best I got was 4c. Fresh air with slow fan about 6c. Outside temp was about 27c at the time.
So it would appear I am ok. Surprising really, I thought it was higher than that. The system was cutting in and out like mad. So on the way home I set the temp at about 22c with medium fan and the system didn't work so hard but it was still cool in the car.

[MULLEY]

SNOW = approx 4 inches, now zero But more snow on its way

[kiwi]

Vanny and Demag you gave me something to look at a bit closer.

The probe was a cellphone older style Nokia, you know one of the ones that dont break so easily. The Temperature gauge is pretty accurate on it but I am guessing that putting it against the grill in the centre of the dash would give such a low reading.

As for the heater beig fully closed well that part it was not because the taps got a small amount of crud that stops the gat as I call it closing properly (another of those will do eventually). Not really worried about a heater when you go a Cool air con system

When you say it cuts out, how do you mean 'cuts out'? Does it simply warm up? Or does a light go out? Or have you an indicator that the compressor pump has switched out?

What light? Did not even realise the basic BX system had a light? The only indicator is the fact it no longer blows cold air seems to be a big indicator its cut out. After I switch it off for ten minutes (time guessing here) it works again. It simply does not like prolonged use! But to be honest I rarely use it for long periods or drives so it does not worry me to often unless one these horrid humid days.

Time to get an electrical tester out I guess or take advantage of a free aircon check ( my bet is that Free means a repair almost certain )

[mat_fenwick]

I have one of those phones too, and the temperature sensor is amazingly inaccurate. Usually reads a few degrees above room temperature, presumably down to the self heating effect of the electronics as it will be within a degree or so when you first turn it on.
We have a customer who sends us one of these to calibrate every year, and although the calibration is more than 10 times the cost of the unit, we are always amazed at the accuracy given the low price. Always within 0.1°C! So, assuming it's not a flukily good one that we see, you could do worse than buy one of them to check out things more accurately.
This old post of mine, with input from AlanS, may help a little also.

[kiwi]

Excellant a useful link. Oh how I miss the great advice that Alan god rest his soul used to give us. At least his memory lives on in the cyber world.

Now you got me thinking about this I will recheck the temp with one of the probes we use at work for temperatures. These are highly accurate (well they better be peoples lives rely on them)

[Vanny]

What light? Did not even realise the basic BX system had a light? The only indicator is the fact it no longer blows cold air seems to be a big indicator its cut out. After I switch it off for ten minutes (time guessing here) it works again. It simply does not like prolonged use! But to be honest I rarely use it for long periods or drives so it does not worry me to often unless one these horrid humid days.

Some of the aftermarket kits i have seen in the UK have a light in the switch between the seats, it simply illuminates if the compressor is running.

It deffinately sounds like your going over pressure and the system is shutting down. The high pressure will very slowly bleed through to the low pressure side, equalising the pressure switch and allowing the compressor to run again. If this is the case then the control module isn't backing the compressor off.

If you cen get a decent thermocouple reader and probe (ideally a K-type thermocouple) then read the minimum temperature that the AC gives at the vent. If your getting negative temps then it will point in the direction of the thermistor!

[Magpi]

dont know how cold it was but myrtle's AC was so cold i could only have it on half
i was driving to Melbourne
it was 37 out side
and i had a jumper on inside the car
i had to keep opening the windows to warm up


i know one of the guys with a mk1 used to get bits of ice flying out of his ac vents into the car

[Vanny]

myrtle's AC was so cold i could only have it on half

Might be teaching to suck eggs, but on the BX you can't have the AC on 'half'. The evaporator (cold bit), in theory, maintains a constant temperature and you add heat to the conditioned air (moisture removed, air chilled) by opening the tap to the heater matrix.

[kiwi]

myrtle's AC was so cold i could only have it on half

Might be teaching to suck eggs, but on the BX you can't have the AC on 'half'. The evaporator (cold bit), in theory, maintains a constant temperature and you add heat to the conditioned air (moisture removed, air chilled) by opening the tap to the heater matrix.

I was thinking that when I read it. So if I think the aircon is cold now just think what it would be like if I fixed that heater tap so it goes right off

Vanny you said about the control module isn't backing the compressor off and the thermistor.

Do I get the impression from earlier comments if they are at fault they are not that easy to reach?