A busy day's work on the BX. 9AM to the man with the long, long 22mm spanner. Two flats on the TX valve lower union showed that it could have been tighter[:I]. I am now running the car about for a month and if the A/C doesn't degrade further, I'll have it gassed up again.
The reversing light switch and the busted strut return pipe were fixed, resorting to a good honest hose clip for the latter. That original clip is a costly nuisance[:(!]; nearly £3 and a swine to fit- don't do it! 60p buys a better solution[;)]
The revelation was the Hydraurincage. I have never been happy with the twitchy steering on this car but a few miles after filling up with orange blood, the ride improved so radically that the penny dropped. One of the spheres must have had a dodgy damper valve because the steering and the ride both came right together[:D][:D]
At last it works like it should do! Despite the filters and reservoir being clean and the old LHM being clean and green, the refilled car still had some bounce in the back end this morning. OH good!
So Thanks to those who helped with the various diagnoses. I'm completely happy with the car at last (but I still lust after a white one...)[:D]
Thanks for your help!
Moderator: RichardW
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tomsheppard
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<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by tomsheppard</i>
So Thanks to those who helped with the various diagnoses. I'm completely happy with the car at last (but I still lust after a white one...)[:D]
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
For goodness sake; paint the bloody thing willya!!!!
http://www.thebugshop.org/bsfqpnt.htm
It'll look like this:-
Alan S
[:D][:D]
So Thanks to those who helped with the various diagnoses. I'm completely happy with the car at last (but I still lust after a white one...)[:D]
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
For goodness sake; paint the bloody thing willya!!!!
http://www.thebugshop.org/bsfqpnt.htm
It'll look like this:-
Alan S
[:D][:D]
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tomsheppard
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No it won't - mine's an estate!
Pretty car though!
Back on the a/c topic, am I right in thinking that with a good differential thermometer, it would be possible to adjust the refrigerant charge to get the maximum cooling?
Is it as simple as outer temp - inner temp = system efficiency. If this were so, gas could be added until the best difference was achieved, allowing me to know if I've got the system fully tuned up.
Pretty car though!
Back on the a/c topic, am I right in thinking that with a good differential thermometer, it would be possible to adjust the refrigerant charge to get the maximum cooling?
Is it as simple as outer temp - inner temp = system efficiency. If this were so, gas could be added until the best difference was achieved, allowing me to know if I've got the system fully tuned up.
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tomsheppard
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tomsheppard
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NB: Alan told me some time ago that he could ice up the screen with his a/c and I have always wondered how that was done. Figuring that he has been a refrigeration engineer, I guessed that he would have the know how to determine exactly the right amount of gas (Mere mortals like ourselves having no chance!). The thermistor though is a super idea. It all comes down to the correct amount of gas though, surely 'cos (if I have this right)too little won't cool enough and too much would saturate the system so the heat couldn't be gotten away. There has to be an optimum amount. I wonder what the tolerance is on that- an ounce, half an ounce?
I have a digital thermometer which I have built which could be used to control the aircon relay. Just how low can you go? I am told that the BX system is one of the best and I'm keen to get the best out of it. You will also be pleased to know Alan that all that useful information you gave me during the job isn't spent as I'm using what I have learned to help another member to convert his own BX. Just what the board is for!
I have a digital thermometer which I have built which could be used to control the aircon relay. Just how low can you go? I am told that the BX system is one of the best and I'm keen to get the best out of it. You will also be pleased to know Alan that all that useful information you gave me during the job isn't spent as I'm using what I have learned to help another member to convert his own BX. Just what the board is for!
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RichardW
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'13 3008 1.6 HDi GripControl - x 1000
Tom,
I am no refrigeration expert, but I am a chemical engineer and I do have a very good understanding how a fridge plant works (actually I think they’re rather clever giving you more cooling than you actually put work in – now, if only we could get cars to run like that!). Anyway, if you consider the liquid filled part of the circuit (the condenser outlet to the TX valve give or take) as a constant volume then if you put more refrigerant in, it must be somewhere and the only place it can be is in the gas side of the system leading to higher pressure. I would therefore be reticent about ‘overfilling’ the system as this is just likely to make it cut out on over pressure.
The system controls the temperature by switching the compressor in and out. If you make the compressor run for more of the time you will get more cooling. Beware, though, that this will probably just ice up the evaporator inside the car sooner or later and then it will stop working until it defrosts again. I have heard that if you run a BX compressor full time the evaporator ices up so much the air flow into the car actually stops and you trip out on high pressure.
I am no refrigeration expert, but I am a chemical engineer and I do have a very good understanding how a fridge plant works (actually I think they’re rather clever giving you more cooling than you actually put work in – now, if only we could get cars to run like that!). Anyway, if you consider the liquid filled part of the circuit (the condenser outlet to the TX valve give or take) as a constant volume then if you put more refrigerant in, it must be somewhere and the only place it can be is in the gas side of the system leading to higher pressure. I would therefore be reticent about ‘overfilling’ the system as this is just likely to make it cut out on over pressure.
The system controls the temperature by switching the compressor in and out. If you make the compressor run for more of the time you will get more cooling. Beware, though, that this will probably just ice up the evaporator inside the car sooner or later and then it will stop working until it defrosts again. I have heard that if you run a BX compressor full time the evaporator ices up so much the air flow into the car actually stops and you trip out on high pressure.
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tomsheppard
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I think mine is running constantly but never getting to maximum cold.
Certainly when first gassed, it had a duty cycle on low a/c settings that has gotten longer. I know that some gas has been lost (And I reckon I've fixed the leak!)so I am trying to reckon up a way of verifying the best amount to top up with because I don't trust my specialist to know enough to be sure of getting it right. The thermometer idea is the best I could come up with but I suppose that with the a/c set to say, half way, the duty cycle would shorten as gas was filled and become shortest at the optimum gas level. Then I'll think about fiddling with the black magic box.
Certainly when first gassed, it had a duty cycle on low a/c settings that has gotten longer. I know that some gas has been lost (And I reckon I've fixed the leak!)so I am trying to reckon up a way of verifying the best amount to top up with because I don't trust my specialist to know enough to be sure of getting it right. The thermometer idea is the best I could come up with but I suppose that with the a/c set to say, half way, the duty cycle would shorten as gas was filled and become shortest at the optimum gas level. Then I'll think about fiddling with the black magic box.
"I'm completely happy with the car at last (but I still lust after a white one...)"
High praise indeed, Tom, knowing your high standards! Beware the post-hydraurincage comedown though: though I haven't experienced it I seem to recall many posts where people have found the hydaurincage period of bliss to be as fickle as a new-sphere honeymoon. Great while it lasts, but a bit perplexing thereafter.
As for the car colour, perhaps what you require is a white paint finish that turns red when the car is in Southampton or en route to France...
High praise indeed, Tom, knowing your high standards! Beware the post-hydraurincage comedown though: though I haven't experienced it I seem to recall many posts where people have found the hydaurincage period of bliss to be as fickle as a new-sphere honeymoon. Great while it lasts, but a bit perplexing thereafter.
As for the car colour, perhaps what you require is a white paint finish that turns red when the car is in Southampton or en route to France...
Richard doesn't really have to tell us he's an engineer; I can tell, trying to make simple things sound complicated....[:D][:D][:D]
These days with "modern" gases they are charged by 'dumping' or 'drop charging' which is effectively drawing a vacuum on the entire system and simply 'pouring' the gas into the system in liquid form as a predetermined amount. In the case of the BX system, it's 1 kg.
The T/X valve, the restriction in the system drops the flow of the high pressure liquid refrigerant from say 130psi to say 6 - 8 psi at which point it vapourises (evaporates) and absorbs heat & as a result boils (as it has a boiling point of around -35) it then returns to the compressor in vapour form where it is compressed in its vapour form which causes it to condense (which is why we have a "condensor") and when compressed it gives up the heat it has aquired in its passage through the evaporator.
The volume of flow through the evaporator is contolled by the restrictor (T/X valve) which cuts off the flow of gas when the end of the evaporator where it connects to the returm line (to the compressor) begins to cool. This is why it's known as a "Thermostatic" Epansion valve. Temperature cuts it off. The trick is to have the gas levels as close to 100% correct as possible otherwise you "flood" the system which can cause the T/X valve to re-open because the evaporator has too high a backpressure and will not come down to optimum pressure (which is proportionate to the temperature reached) and too little will cause the return to go to vacuum which will ice the early part of the coil whilst leaving the T/X wide open; in other words there is too much empty space within the system and no coldness reaching the sensing part of the T/X.
The receiver/dryer is built into the system to allow for a reserve supply of gas over & above what the system actually needs to work to optimum performance which is effectively "pumped down" into it when a system with a correct operating gas level is cutting out as it should on the T/X and is there to cope with any extra load suddenly imposed such as opening all doors on a hot summers day. This is why that thing is as large as it is; a bit of silica-gel or similar in the bottom and the rest of that cylinder just empty space to carry/store the liquid refrigerant.
In commercial refrigeration applications, and before the days of "Greenhouse Emission" laws and the like, the condensor sat on a receiver that could carry anything up to 10kgs and when charging these systems, it was required for everything to be down to temperature in the coldroom or cabinet, T/X cutting in & out as it should and the gas to be fed into the system until liquid refrigerant came from the cock on top of the receiver. Just simply filled like a water tank.
So the moral of the story is, just get the system operating to full efficiency, recirculate the air in the car and control the temperature via a thermister & it should all work well enough to freeze the windscreen if that's what you want.
Incidentally, on the BX, the slide control on the dash rarely if ever works, so what is possibly happening is that the compressor is not cutting out as you suspect. This doesn't give you the best performance as you're drawing the air over a coat of ice rather than over the actual coil which will absorb the heat. (The ice will melt off the coil once the system begins to cycle properly) If you have any leaks through the air ducts leading to the front of the car, that is adding even further load and adding moisture to the coil, and as we soon discover where I am, with a high humidity content, the coil will actually frost over in a matter of minutes if the "fresh air" switch is left open instead of the "recirculate." This will lead to a dramatic loss of temperature.
Happy freezing....[8D][8D][8D][8D][8D]
Alan S [:o)]
These days with "modern" gases they are charged by 'dumping' or 'drop charging' which is effectively drawing a vacuum on the entire system and simply 'pouring' the gas into the system in liquid form as a predetermined amount. In the case of the BX system, it's 1 kg.
The T/X valve, the restriction in the system drops the flow of the high pressure liquid refrigerant from say 130psi to say 6 - 8 psi at which point it vapourises (evaporates) and absorbs heat & as a result boils (as it has a boiling point of around -35) it then returns to the compressor in vapour form where it is compressed in its vapour form which causes it to condense (which is why we have a "condensor") and when compressed it gives up the heat it has aquired in its passage through the evaporator.
The volume of flow through the evaporator is contolled by the restrictor (T/X valve) which cuts off the flow of gas when the end of the evaporator where it connects to the returm line (to the compressor) begins to cool. This is why it's known as a "Thermostatic" Epansion valve. Temperature cuts it off. The trick is to have the gas levels as close to 100% correct as possible otherwise you "flood" the system which can cause the T/X valve to re-open because the evaporator has too high a backpressure and will not come down to optimum pressure (which is proportionate to the temperature reached) and too little will cause the return to go to vacuum which will ice the early part of the coil whilst leaving the T/X wide open; in other words there is too much empty space within the system and no coldness reaching the sensing part of the T/X.
The receiver/dryer is built into the system to allow for a reserve supply of gas over & above what the system actually needs to work to optimum performance which is effectively "pumped down" into it when a system with a correct operating gas level is cutting out as it should on the T/X and is there to cope with any extra load suddenly imposed such as opening all doors on a hot summers day. This is why that thing is as large as it is; a bit of silica-gel or similar in the bottom and the rest of that cylinder just empty space to carry/store the liquid refrigerant.
In commercial refrigeration applications, and before the days of "Greenhouse Emission" laws and the like, the condensor sat on a receiver that could carry anything up to 10kgs and when charging these systems, it was required for everything to be down to temperature in the coldroom or cabinet, T/X cutting in & out as it should and the gas to be fed into the system until liquid refrigerant came from the cock on top of the receiver. Just simply filled like a water tank.
So the moral of the story is, just get the system operating to full efficiency, recirculate the air in the car and control the temperature via a thermister & it should all work well enough to freeze the windscreen if that's what you want.
Incidentally, on the BX, the slide control on the dash rarely if ever works, so what is possibly happening is that the compressor is not cutting out as you suspect. This doesn't give you the best performance as you're drawing the air over a coat of ice rather than over the actual coil which will absorb the heat. (The ice will melt off the coil once the system begins to cycle properly) If you have any leaks through the air ducts leading to the front of the car, that is adding even further load and adding moisture to the coil, and as we soon discover where I am, with a high humidity content, the coil will actually frost over in a matter of minutes if the "fresh air" switch is left open instead of the "recirculate." This will lead to a dramatic loss of temperature.
Happy freezing....[8D][8D][8D][8D][8D]
Alan S [:o)]
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RichardW
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"The T/X valve, the restriction in the system drops the flow of the high pressure liquid refrigerant from say 130psi to say 6 - 8 psi at which point it vapourises (evaporates) and absorbs heat & as a result boils (as it has a boiling point of around -35) it then returns to the compressor in vapour form where it is compressed in its vapour form which causes it to condense (which is why we have a "condensor") and when compressed it gives up the heat it has aquired in its passage through the evaporator."
Well, nearly! As the pressure drops across the T/X valve, energy within the refrigerant is used to vaporise part of the refigerant - this causes the temperature to drop (technically, an adiabatic flash). This vapour / liquid mixture than passes to the evaporator where heat moves from the air to the refigerant (thus cooling the air and causing the remainder of the refrigerant to boil). The cold, low pressure refrigerant vapour then passes to the compressor, where it is turned into hot, high pressure vapour. This than passes to the condenser, where it is turned back into a warm high pressure liquid by giving up heat to the air (the heat given up here is the heat taken from the evaporator, plus the energy (heat) added by the compressor). The warm liquid then passes back to the T/X valve to start all over again.
Just being pedantic - but I suspect Alan's practical experience & knowledge is much more useful than my theoretical stuff!
Well, nearly! As the pressure drops across the T/X valve, energy within the refrigerant is used to vaporise part of the refigerant - this causes the temperature to drop (technically, an adiabatic flash). This vapour / liquid mixture than passes to the evaporator where heat moves from the air to the refigerant (thus cooling the air and causing the remainder of the refrigerant to boil). The cold, low pressure refrigerant vapour then passes to the compressor, where it is turned into hot, high pressure vapour. This than passes to the condenser, where it is turned back into a warm high pressure liquid by giving up heat to the air (the heat given up here is the heat taken from the evaporator, plus the energy (heat) added by the compressor). The warm liquid then passes back to the T/X valve to start all over again.
Just being pedantic - but I suspect Alan's practical experience & knowledge is much more useful than my theoretical stuff!
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tomsheppard
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