TD5 Airconditioner efficiency.

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Originally Posted by shack

Neither of the defender TD5 ECU's (main engine and AC) monitor system pressure when engaging the condenser fan, there is only a low/high pressure switch which is used for hard off/hard on switching of the compressor.

Later vehicles obviously do monitor pressure and adjust displacement valves and fans etc..

I can adjust the main engine ECU to control the condenser fan differently, but I'm not sure it will help in the above situation.

Other things to consider...the defender evaporator is situated just above the floor and has no intake filters at all, so they get filled with crud.

I've cleaned my evap and made filters to stop it happening again.

They don't have a variable displacement compressor. The early type defender condenser is serpentine and has no fan, the late is parallel flow and has a fan. The early has an old school thermostat, the late has a thermistor and ECU, I think the ECU's or thermistors commonly fail, how many I don't know, but I don't trust them.

The last couple days have been around 23-27° and I'm getting about -6°air blowing out of the unit, if it's humid the evaporator will freeze at these temps pretty quickly, I have made my own control setup so I can select what I want it to do.

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The problem I've had is when it's really hot - unless the air coming out of the AC is really cold it doesn't do stuff. It needs to work like an actual ac unit.

So after reading the manual there are two fuses in the cabin Fuse 28 (ac blower) and fuse 29 (ac compressor realay /cooling fan relay). They are problably ok but the two relays under the drivers seat relay #1 and #2 are just described in the manual as "a/c relay if fitted". I might have a little look at them. I've had #4 the main relay play up in the past and it was not pleasant. So I'm suspicious of those relays.

I've never seen the fan run although the AC guy said he's seen it run.

The relay under the seat for the compressor often fails, the female terminals in the socket stretch over time and heat cycles.

The condenser fan will almost certainly NOT run all the time the AC is on, only when ambient conditions (including engine temp) and roadspeed triggers are reached.

If the ambient temp is under 30°and the car is stationary, it probably won't run.

Where I live, ambient temp can often be 40-43°, the fan will run all the time then.

But I need to check all of this!!

Quote:

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Originally Posted by shack

The relay under the seat for the compressor often fails, the female terminals in the socket stretch over time and heat cycles.

The condenser fan will almost certainly NOT run all the time the AC is on, only when ambient conditions (including engine temp) and roadspeed triggers are reached.

If the ambient temp is under 30°and the car is stationary, it probably won't run.

Where I live, ambient temp can often be 40-43°, the fan will run all the time then.

But I need to check all of this!!

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The loose terminals was what was wrong with the "main relay" which would cause the car to stop! I gave them a tweak and hasn't missed a beat since.

As to if the temp is less than 30 the fan won't run.. this is crazy! 28 is warm enough to want the ac to work! I wonder if this was done with half an eye on engine temps to stop the engine getting too low.

The engine can't really get too low, the thermostat would simply close. Also the condenser fan (see my post a while back) is by far not capable enough to cool the engine by itself (also see a long thread by keithy regarding thermofans). It is used in conjunction with the VC fan on the P38 and I reckon it might also be on the defender to help cool the engine during idle / stop and go traffic where the VC fan would simply not pull enough air on hot days through the radiator. The condenser fan is simply helping at that point but not by much.

Mind you 30c ambient outside temp is warm for us, but for the AC it is not that much work. The refrigerant only needs to be 15c higher to do a decent job transferring heat to the surrounding air and as you know, the VC fan would already be displacing a decent amount of air through the condenser at that point.

At 45c ambient, that's where the "fun" starts. For the condenser to transfer its heat properly, you would again want a 15c difference or there abouts which makes the bloody thing 60c and that means the compressor needs to work a lot harder. It also means the temperature of the air going into the engine radiator has been heated up quite a bit as well and needs to work that much harder.

Like I suggested, make a shunt (or jumper) cable now that you can find the condenser fan relay and jump the fan to see what the behaviour is when idle with the fan on constantly.

Shack also mentioned: no filters for the evaporator, that will limit its functioning quite drastically when dirt gets in. Perhaps you found the culprit? ;)

Cheers,
-P

Here we go...

Apologies for my earlier post (no. 30).

I've had the post edited to point out my error for other users later on.

The defender TD5 - supposedly all models with "factory" air, will have an AC ECU located in the under dash bolt in unit, behind the drivers side speaker and AC controls.

This little unit performs a number of functions.

1. It interprets the resistance from the thermistor in the evaporator to provide 3 different temp settings and to prevent evaporator freezing.

2. It uses the signal from a "trinary" pressure switch to assess 3 things.

Firstly, whether system pressure is high enough for the compressor to engage - low pressure safety cut out.

Secondly whether system pressure is low enough for the compressor to engage - high pressure safety cut out.

And thirdly whether system pressure is high enough to request the condenser fan to be engaged.

It then passes all these requests to the engine ECU, as the engine ECU is the one that actually controls the compressor and the condenser fan.

On my vehicle, the condenser fan comes on @ 225psi and switches back off @ 188 psi, so that's 37psi hysteresis, that will be to prevent the fan from constantly switching on and off.

The system does NOT monitor vehicle speed or ambient temp AT ALL, all condenser fan operation for condenser cooling is based on pressure alone.


For comparison on a Discovery 2 (which I'm more familiar with as I've had them for years) condenser cooling fan operation is controlled by the ATC - Air temperature control ECU (aka HVAC).

The fan is switched on if vehicle speed is 80kmh or less while air temp is 28°c or more.

It switches back off if either vehicle speed increases to 100kmh or ambient air temp drops to 25°c or less.

The D2 ATC does NOT monitor system pressure at all for condenser fan operation, it only uses a 2 pin pressure switch to low pressure cut out and high pressure cut out.


This took a while to sort out so hopefully it's of use to everyone with a TD5 defender that has poor AC.

I'm running different condenser fan operation and different temp control as well, (override but keeping all safety monitoring in place) although I'm still looking to change that for better operation.

Without my mods, the unit routinely puts out 15° air, although I think my AC ECU is on the way out and may be causing this.

*Note, both vehicles also use the condenser fan for engine cooling once preset coolant temps are reached.

Quote:

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Originally Posted by shack

Here we go...

Apologies for my earlier post (no. 30).

I've had the post edited to point out my error for other users later on.

The defender TD5 - supposedly all models with "factory" air, will have an AC ECU located in the under dash bolt in unit, behind the drivers side speaker and AC controls.

This little unit performs a number of functions.

1. It interprets the resistance from the thermistor in the evaporator to provide 3 different temp settings and to prevent evaporator freezing.

2. It uses the signal from a "trinary" pressure switch to assess 3 things.

Firstly, whether system pressure is high enough for the compressor to engage - low pressure safety cut out.

Secondly whether system pressure is low enough for the compressor to engage - high pressure safety cut out.

And thirdly whether system pressure is high enough to request the condenser fan to be engaged.

It then passes all these requests to the engine ECU, as the engine ECU is the one that actually controls the compressor and the condenser fan.

On my vehicle, the condenser fan comes on @ 225psi and switches back off @ 188 psi, so that's 37psi hysteresis, that will be to prevent the fan from constantly switching on and off.

The system does NOT monitor vehicle speed or ambient temp AT ALL, all condenser fan operation for condenser cooling is based on pressure alone.


For comparison on a Discovery 2 (which I'm more familiar with as I've had them for years) condenser cooling fan operation is controlled by the ATC - Air temperature control ECU (aka HVAC).

The fan is switched on if vehicle speed is 80kmh or less while air temp is 28°c or more.

It switches back off if either vehicle speed increases to 100kmh or ambient air temp drops to 25°c or less.

The D2 ATC does NOT monitor system pressure at all for condenser fan operation, it only uses a 2 pin pressure switch to low pressure cut out and high pressure cut out.


This took a while to sort out so hopefully it's of use to everyone with a TD5 defender that has poor AC.

I'm running different condenser fan operation and different temp control as well, (override but keeping all safety monitoring in place) although I'm still looking to change that for better operation.

Without my mods, the unit routinely puts out 15° air, although I think my AC ECU is on the way out and may be causing this.

*Note, both vehicles also use the condenser fan for engine cooling once preset coolant temps are reached.

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I'd just like to thank you for putting all this together.. very useful.

So the update is that after the evaporator clean the system is now working **much** better. I can't say for sure that they didn't tweak something else, but the effectiveness is very much improved.

On a 27 degree brisbane day it was running at between 4 and 6 degrees with the car moving (possibly the best result I can remember recording). When the vehicle was stopped in traffic it went up to 10-12. Again a good result by historical perspective.

When the car was stopped spraying the condenser with water resulted in an instant significant drop in the temps. I have not seen the fan run - however the AC shop claimed that they have seen it run. I think there is more to be done in this space. A lot of my usage is crawling over sand dunes often at low speeds in high temperatures. Would be great to get some improvements here.

For the moment then next stage is to fix the new fault. it's not the fan because the noise can be turned off and on with the ac switch independent of fan. :|]

https://youtu.be/wlhpBw-8hJ8'si=7PNtWTRfTogOQeLN

Great write-up shack! that means that the TD5 mostly works as the P38 system does.

The one thing I can not yet figure out is why the AC would put out 15c without the condenser fan running. The only reason I can imagine is that the compressor is simply not running fast enough at idle to provide sufficient amounts of gas ie. superheat as it is called I believe. This means that the gas evaporates inside the evaporator completely before it has passed all the way through and it can not absorb more heat from its surrounding, in other words can't cool enough.

Using the P38 once again as reference; a quick google search resulted in finding the same compressor for a number of landrover vehicles including the P38, disco 2, defender. The denso part is JPB101330 which is a 155cc unit usually. As far as I can remember it usually worked just fine in stop and go traffic also on hot days but it did cut out every now and then but I wrote that down to the BECM limiting current usage in the P38. The pulley ratio I am not entirely sure about but my guess is it is mostly the same across all the vehicles, maybe a bit bigger on diesel engines since they rev less.

The fact that you can cool the condenser and get colder air does suggest there is something to be gained by letting the condenser fan run perhaps. Still, the pressure is simply not high enough in the system to warrant that thing running. 225 psi is around 15 bar which sort of matches the P38's setting, in any case you can check the temperature of the condenser (on the hot side) to see where the pressure us roughly at: 225psi / 15 bar is around 56c so if you read a temperature lower than that, it makes sense the fan is not running.

Cheers,
-P

Quote:

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Originally Posted by prelude

The one thing I can not yet figure out is why the AC would put out 15c without the condenser fan running. The only reason I can imagine is that the compressor is simply not running fast enough at idle to provide sufficient amounts of gas ie. superheat as it is called I believe.

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It's simpler than that. Cooling is fundamentally proportional to mass flow of refrigerant. A compressor compresses gas. The lower the compression ratio the more efficient it is. So for a fixed rotation speed, the lower the condenser temperature the more gas the compressor will move.

It's also proportional to the temperature of the condensed liquid, although cooling the liquid to expansion temperature is a sensible cooling rather than latent so it's not a massive contributor.

Of course, running the compressor faster moves more mass.

So the cooler you can get the condenser, the more efficient the compressor and the more cooling.

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Originally Posted by BradC

It's simpler than that. Cooling is fundamentally proportional to mass flow of refrigerant. A compressor compresses gas. The lower the compression ratio the more efficient it is. So for a fixed rotation speed, the lower the condenser temperature the more gas the compressor will move.

It's also proportional to the temperature of the condensed liquid, although cooling the liquid to expansion temperature is a sensible cooling rather than latent so it's not a massive contributor.

Of course, running the compressor faster moves more mass.

So the cooler you can get the condenser, the more efficient the compressor and the more cooling.

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But if it doesn't spin fast enough at idle to get the fan to run it's never really going to get cold at low engine speeds. I'm going to have to test this to see if it actually runs. I know I need to do some testing. I can't wonder what they were thinking with the design...