Recently replaced the pump, filter and dash switch (and heater matrix). Air con system now holds pressure but will not run continuously when switched on. The system runs for a minute or so then cuts out (fans and pump clutch included); then after 30 secs or so cuts back in again as if it was being controlled by a thermostat. As I understand it there is no thermostat controlling the system on this model (unlike later climate control set-up on the HDi). When you switch it on it should run and stay running until switched off. Have tried running an external 12v supply to pressure switch connection on top of the filter/drier unit and lo and behold the system runs continuously. Is there anything else that controls the system?
Can anyone help please.
Thanks - Peter
Update - 1630 29.04.04 All relays have now been replaced - problem remains.
Xantia Air con problem - 1.9TDSX Est
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OnlineRichardW
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Peter,
The connection on top of the filter is a pressure switch - it probably has both under and over pressure functions, and I suspect that yours is cutting out on over pressure. It may just be a dodgy switch or it may be more serious. The Bitron unit is the electronic controller, down by the LH head light somewhere - this would appear to be working as it is shutting the air con down!
Alan S may be along later, and he may be able to shed some more light as he is air-con trained, but I fear a specialist visit is on the cards...
The connection on top of the filter is a pressure switch - it probably has both under and over pressure functions, and I suspect that yours is cutting out on over pressure. It may just be a dodgy switch or it may be more serious. The Bitron unit is the electronic controller, down by the LH head light somewhere - this would appear to be working as it is shutting the air con down!
Alan S may be along later, and he may be able to shed some more light as he is air-con trained, but I fear a specialist visit is on the cards...
Does the fan come on when the compresser is on? The fan must be on when compresser is working or else the pressure in the air con system builds up quickly and the pressure sensor comes in to play and cuts the supply off to the compresser.There is also a evaporater senser which can play up which can cause the supply to the compresser to be stopped.Also are you sure the correct amount of refriderent is in your system as too much can cause problems too!
At present the fans and pump operate at all times when dash switch is made. It was not always thus. For instance, at one stage only the fans would come on when the dash switch was made due to there being insufficient refrigerant pressure. I have not heard of a sensor on the evaporator. Is this a thermostatic device and where on the car is it? It would be helpful to know exactly what sensors there are and precisely where in the circuit they operate. If I understand correctly the dash switch supplies both the Bitron unit (which controls the fans) AND the pressure sensor which supplies the pump clutch solenoid. Presumably the evap sensor is in series with the clutch solenoid and would therefore turn the system off if it ran too cold.
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volcaneoptimist
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It's interesting reading but I get more confused especially when CRD717 mentioned that there is no thermostat controlling the aircon system. What cross my mind is how could one control the temperature inside the cabin without a thermostat which is an essential device in aircon or refrigerant system. I am not an expert and have been wrong before, but surely there's a knob to turn the temperature setting which is usually positioned next to the knob/dial controlling the speed of the blower fan. My guess is that the thermostat is at the back of the knob/dial. Hope I am not wrong again as our cars here are not equip with dual climate control for winter and summer. Anyway, I hope you managed to solve the mystery and get your aircon system running as it should be.
Now I am going to learn something here but there is a thermostat in the system. It is behind the alarm warning light on the dash.
However is it possible that this only controls the water flow through the matrix and as said earlier the A/C runs continuously?
When the A/C is used with the heater running to dry the air on wet and cold days the heater still holds the cabin temp stable.
Robin
However is it possible that this only controls the water flow through the matrix and as said earlier the A/C runs continuously?
When the A/C is used with the heater running to dry the air on wet and cold days the heater still holds the cabin temp stable.
Robin
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Richard Gallagher
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The evaporator sensor (pressure relief valve) is positioned on the evaporator itself, behind the pollen filter.
It regulates the refrigerant flow and stabilises the evaporation pressure of the fluid in relation to the temperature at the evaporator outlet.
It transforms the fluid into a saturated stream at low pressure and temperature.
The pressostat, on the top of the dehydrator reservoir, is a safety device which cuts the operation of the compressor in the event of over pressure, or pressure too low in the system.
These are the only two sensors on the air con system itself. A third sensor controlling the temperature inside the car sits behind the alarm LED.
It regulates the refrigerant flow and stabilises the evaporation pressure of the fluid in relation to the temperature at the evaporator outlet.
It transforms the fluid into a saturated stream at low pressure and temperature.
The pressostat, on the top of the dehydrator reservoir, is a safety device which cuts the operation of the compressor in the event of over pressure, or pressure too low in the system.
These are the only two sensors on the air con system itself. A third sensor controlling the temperature inside the car sits behind the alarm LED.
..and as Robin also surmises, this third sensor merely controls the waterflow through the heater matrix and operates entirely independently of the aircon system. I too believe this to be the case. Does anyone know better?
He also mentions the drying effect of airconditioning. I often get sudden and almost total misting up whilst using the aircon and heater on the screen, particularly on cool evenings. I wonder if this has any bearing on the intermittent running of my system (the heater matrix was replaced late last year).
He also mentions the drying effect of airconditioning. I often get sudden and almost total misting up whilst using the aircon and heater on the screen, particularly on cool evenings. I wonder if this has any bearing on the intermittent running of my system (the heater matrix was replaced late last year).
Most of the refrigeration systems I worked on were based on "Tractor technology" as opposed to the electronically operated stuff we see today. However I can tell you that there is no way that the temperature will be uncontrolled. On our BXs they have what amounts to a thermister which is controlled via what appears to be a variable resister set up and thereby controls the temp.
If yours has the same thing, there could be a couple of reasons; firstly, if your mechanic who fitted the matrix found the thermister/sensor for the temp control floating around and couldn't remember where it was mounted & got it into his head that it had something to do with the air/con & so mounted it in the direct path of the air <b>leaving</b> the evaporator rather than in the path of it <b>returning</b> to it, that will cause the problem real easily as it will then be working off evaporator temp rather than cabin temp.
As has been suggested, the switch on the receiver/dryer depending on the specs as applied to your installation (like everything, regulations are constantly changing & do so from country to country, so we don't have a strict set of specs to work to) is most likely a dual setting. In other words it will cut out if the pressure gets too high (say due to moisture or blockage in the system) or if it gets too low (again due to a blockage or moisture in the system, or gets short on gas.)
With later gases, R134a for example, the gas level really can no longer be checked as was the case with the old R12 systems via the sight glass on top of the filter/dryer; R134a <b>always</b> looks milky regardless of the gas charge level. It has to be done via a fridge mechanic with the gauges. By passing this switch is a recipe for a disaster as it is there to prevent the compressor tying itself in a knot in the case of too high a pressure or from allowing it to draw into vacuum if too low & thereby sucking oil into the compressor & pumping it through the system creating a major problem for a repairer to get it out. A compressor slugging oil can also lock up & destroy itself.
If possible I would suggest firstly finding access to the TX valve and checking to see if there's any signs of oil leaks around it. This could be the reason if the system is low on gas. At teh same time, try & find the temp sensor; this will possibly be in a round black plastic container about an inch diameter with a mesh type of cover at the top & two wires coming from it. Start the system & hold that in your hand & see if that makes a difference.
At least if you access both of these items, anyone having to check the system should do it at a reasonable cost as access is usually the most expensive part of the entire exercise.
Hope that helps point things in the right direction, but in all honesty, I feel this may be just out of the realms of a DIY job without the equipment or the experience.
Alan S
If yours has the same thing, there could be a couple of reasons; firstly, if your mechanic who fitted the matrix found the thermister/sensor for the temp control floating around and couldn't remember where it was mounted & got it into his head that it had something to do with the air/con & so mounted it in the direct path of the air <b>leaving</b> the evaporator rather than in the path of it <b>returning</b> to it, that will cause the problem real easily as it will then be working off evaporator temp rather than cabin temp.
As has been suggested, the switch on the receiver/dryer depending on the specs as applied to your installation (like everything, regulations are constantly changing & do so from country to country, so we don't have a strict set of specs to work to) is most likely a dual setting. In other words it will cut out if the pressure gets too high (say due to moisture or blockage in the system) or if it gets too low (again due to a blockage or moisture in the system, or gets short on gas.)
With later gases, R134a for example, the gas level really can no longer be checked as was the case with the old R12 systems via the sight glass on top of the filter/dryer; R134a <b>always</b> looks milky regardless of the gas charge level. It has to be done via a fridge mechanic with the gauges. By passing this switch is a recipe for a disaster as it is there to prevent the compressor tying itself in a knot in the case of too high a pressure or from allowing it to draw into vacuum if too low & thereby sucking oil into the compressor & pumping it through the system creating a major problem for a repairer to get it out. A compressor slugging oil can also lock up & destroy itself.
If possible I would suggest firstly finding access to the TX valve and checking to see if there's any signs of oil leaks around it. This could be the reason if the system is low on gas. At teh same time, try & find the temp sensor; this will possibly be in a round black plastic container about an inch diameter with a mesh type of cover at the top & two wires coming from it. Start the system & hold that in your hand & see if that makes a difference.
At least if you access both of these items, anyone having to check the system should do it at a reasonable cost as access is usually the most expensive part of the entire exercise.
Hope that helps point things in the right direction, but in all honesty, I feel this may be just out of the realms of a DIY job without the equipment or the experience.
Alan S