Aircon woes

[pannawonica]

Recently I had a Tx valve fitted under warrenty and the aircon worked better than ever from new. My Puma is 8 months 15 Km old. Yesterday travelling back from Karratha in the heat all it would do is blow warm air :mad:. I went outside today and with the vehicle under the carport ran the aircon checking the temperature output with an accurate probe. The system quickly and consistantly pulled down to around 5 deg centigrade. As Pauline would say " Please explain ? " To me aircon is a bit of a dark art. :D

[PAT303]

You don't have a set of bad arse cook a roo at 100 yards set of spotties on the front do you?. Pat

[pannawonica]

Err actually yes, Lightforce Genesis HID bin wondering about them, however it never had any effect on my TD5 Disco or the V8 Disco.

[Davehoos]

nothing like spot lights and roo bars at hyway speeds to overheat the system.
the answer is to make the air pressure in the engine bay low enough to draw the air through.

what caused the TX replacement.is the compressor a variable capacity pump.

did it freze up or was the condensor over pressure.what other bits should have been replaced.the gas quantity is critical as the temp rises-you find the car will go all year over gassed untill a hot day and no room for the liquid.

any crap in the system collected in the dryer lowers the liquid line pressure and tells the TX not to work as hard.if it freezes up the pump stop working.

these green sytems always work when tested-but not when tested.

dark art-----correct.they cant teach vibe.
there is no way to make green air conditioning with undersized condensor work,they need a small liquid line coole[calling this subcooler] or my favorite an accumilator and a liquid catch tank.

[pannawonica]

Yes I think you have made a couple of good points. From my understanding the dryer is also a filter and a pressure differential affecting the TX valve. Regarding the Roo bar I have an ARB and an insect screen, however I have a big arsed standard ducted fan drawing the air through. The Tojos at work all run spotties and bar work , like my Puma and seem to work OK. However I would consider upgraded parts or additional installations required. Her indoors would like to improve the aircon no argument there. Do not understand vibe, but your advice of bigger condenser make good sense just like a upgraded intercooler.It is my belief that the system did not freeze up and that it was under powered. Weeks earlier when the weather was cooler it worked just fine , which would support what you have advised.

[pannawonica]

What I neglected to say that from new it had been low on gas as advised by dealer, yes I know. They topped it up twice til I spit the dummy. They eventually admitted a faulty TX. However I cannot be sure.

[P38ace]

In replacing the TX valve they did not necessarily fix the initial problem. As well as the Tx valve I'm told there is also a temperature sensor, which I had replaced under warranty 3 times before they got a "special, tested, guaranteed to work one" from LR UK.

Also check under the bonnet that your heater valve is actually closing fully. That's another long story. :mad:

[Davehoos]

dealers often replace TX valves out of frustration.im guessing it has a electronic controlled variable capacity pump.

TX controlls the flow of liquid by restricting the liquid line creating vapour.when the vapour temp drops bellow the preset temp most open up and dump liquid into the evaporator basically defrosting it.other brands TX block off the flow untill the temp returns to the presset.
if the low side pressure is bellow normal the pistons dont stroke as much and the high pressure reading drops-so the checker say it low on gas.

with these new systems your sopossed to use laser temp guns.when i have i found blocked condencors.the heat change was so high that when water was sprayed on it dryed in spots.

have done dozens of degas/regas to allow them to remove the insides.
often it was the insides of the european hoses had colapsed or was leaking through the very thin alloy pipes.

dryers are not covered normally by warranty as it a service item-but it should be replaced every time.the new sub cooler condencors most you can replace the desicant and give it a quick clean but realy the should be replaced as a job lot.

Teaching VIBE.
it easy to teach someone the look at a pressure chart and a diognostics chart.trust me that often doesnt get these to work.
most of the time you can diognose troublesome cars parked in the driveway by have a friendly chat..you discard most of what they have been previously told-my old boss luved to connect gauges to the vehicle and remove the grill..this had more to do with showing you know how to get the bonnet up.

[Davehoos]

however I have a big arsed standard ducted fan drawing the air through

original?can you here it working when warm?

insect screens-often have to be removed for hyway work.have been fitting shade cloth over the bumper allowing air to come around behind.

nissn patrol had issues around 110kmh at 120 they cooled.some had different numbers of fans some had none with some running on pressure and some temperature.it was an air flow issue with air going over the cab and not through the radiator.

[pannawonica]

The viscous fan is working well moving large volume of warm air. The insect screen ARB type has 5mm by 4 mm holes. My previous Disco TD5 had the shade cloth on the roo bar type and worked fine. The dealer use an outside contractor for aircon and may not be as up todate as yourself Davehoos.
However do you think its worth testing minus screen? I am a little reluctant to remove spotlights due to the fact I drive down to Perth usually at night. Thanks John.

[PAT303]

Remove both the screen and lights for one trip and see what happens. Pat

[pannawonica]

Pat I recon thats the way to go, similar heat and time of day to replicate conditions. This will if need be put me in a better position when talking to the stealer. However I don"t think my bar, lights front end set up would actually be that unique and am surprised this has not been previously observed.
It will be few days before I can try this as I"m back at work.:D

[rick130]

The basic vapour/compression refrigeration cycle.

Compressor.

As it's name suggests, it takes a low pressure gas and compresses it to a higher pressure.
As a gas is compressed it also increases in heat.

This now high pressure and hot gas, known as a super heated vapour is leaves the compressor, travels along the discharge line and into the condenser.
The discharge gas inside the condenser tubes cools as ambient air flows over the fins and coils and ultimately, cools it enough so that it condenses into its liquid state by the last pass of the coil, although its pressure is still (almost) equal to the pressure it left the compressor.

This now saturated liquid is pushed through the liquid line to the filter/dryer/receiver.
In a car AC system this item performs three functions (in house fridges or commercial refrig systems it doesn't act as a receiver)

It is designed to handle excess liquid capacity (necessary if using a TX valve type expansion device) as well as filtering and drying the refrigerant.
Usually the desiccant performs both jobs and is little balls of activated alumina, trapped in the dryer by screens and often glass fibre mats.

It's very easy to check for a partially blocked dryer, there will be a temperature difference between the inlet and outlet liquid temps.

Your touch is all it takes to sense this ;)

The still high pressure saturated liquid continues through the liquid line to the expansion device, in this case it sounds like a Thermostatic Expansion valve, but may be a fixed orifice, capillary tube, electronic expansion valve, etc.
The expansion device can be anything that throttles the flow of liquid with a tiny orifice.

What happens as the high pressure liquid is forced through the orifice is that it will start to expand as it enters the larger volume of the evaporator tube/s and as it does so it will absorb heat from its surroundings.

As the now expanding liquid travels through the evaporator it continues to boil and absorb heat.
Air flow across the evap coil is critical here, any blockage or restriction of air flow across the evaporator reduces the ability of the expanding liquid refrigerant to absorb more heat.

The TX valve regulates the flow of refrigerant entering the coil to changing evaporator loads by means of a feeler bulb/sensor at the evaporator outlet that is filled and sealed with refrigerant.
A small capillary tube goes back to the TX valve where it opens into a large diaphragm atop the valve.
This diaphragm is connected by a pushrod and spring arrangement to the inlet needle of the valve.

This mixture of gas and liquid in the sensor (known as a power element) responds in a known way to changes in temperature and so exerts pressure on the diaphragm in the valve, modulating a tapered needle in the orifice to changes in evaporator outlet temperature.

Hopefully, if everything is setup, sized and adjsuted correctly all liquid refrigerant has boiled off by the time it gets to the end of the evaporator.

As an aside, systems that use a fixed length capillary tube instead of a TX valve for expansion duties (eg. House fridge) do not use a receiver in their system, they have a fixed amount or refrigerant in the system known as a critical charge and the dryer cannot be mounted horizontally but vertically, otherwise it acts as a receiver, which really upsets the systems balance, but I digress......

Anyway, the the now saturated vapour travels along the suction line from the evap to the compressor, enters the compressor and starts its journey again.

The things that can jigger a TX valve are
1. crap in the inlet blocking the inlet screen.
2. moisture (if there's excess moisture in the system that the dryer can't handle, it will instantly freeze in the TX orifice) This is the same as turning the valve 'off'. It won't restart until the compressor is turned off and the temp of the valve rises above 0*C
3. broken or perforated capillary or power element. This is the same as turning a valve off. The inlet needle shuts under spring pressure and no refrigerant can flow.
4. wear (many, many years of use)

Under extremes of temperature I've seen dryers on commercial refrig systems 'release' moisture into the system, instantly freezing the TX valve internally.

I'd reckon it must happen more frequently on cars as
a) the underbonnet temps can be insane
b) all due respect but from my observations most car mechanic's that work on car ac systems don't have the best of work practices.
AC/refrig systems are extremely sensitive to moisture and as soon as the system is opened it is absorbing moisture from the surrounding air.
This includes the gas and more particularly the oils. A lot of car mechanics IME don't appear to appreciate this.

I've deliberately neglected any pressure switches and temp sensors that are mounted along the way as they can vary according to application and can usually be checked pretty quickly with a multimeter if opened/closed.

[Davehoos]

puma was mentioned.

so Im guesing its a modern system.you mentioned it was fitted by an after market dealer.

the older defenders with the AMC system had a sanden compressor with a good receiver-filter-dryer.
the denso compressor up dated on later cars is much the same.

some of the later defenders had a imported system.some have a removable dryer that is located in the liquid section of the condencor.
the idea is that liquid is cooled after it has changed state but pressure stays much the same.

most cars are going to a subcooler system that all about reducing gas volume.

the AMC uses the old TX valve with screen and capilery bulb.
the new denso systems use a block valve with the temp sencor inside the vapour suction port.

the dyres decompose into a dirt-and the older landrovers use coated steel pipes that also circulates.the denso pumps use teflon type products to coat alloy contact parts.oil over heats and turns into a black crap and the hose lining.