How to improve factory AC?

[KiwiBacon]

My nissan work car has terrible air-conditioning. I actually thought something was wrong with it, but everything checks out and the vent discharge temps are right in line with the FSM 9-12C at 25C ambient. It makes the AC in my RRC feel awesome.

It's a simple system with a variable displacement compressor, which according to the FSM is there to prevent the suction pressure going too low at higher engine rpm. It appears this AC system was only intended to defog windows and/or Nissan have set it up so it can't hurt your fuel economy too much.

So what can be done? Some guy in Malaysia is reporting noticable improvements by lagging the HP line from the condensor to the TX valve. Are the TX valves adjustable? I live in a very dry area so icing isn't a big concern.

[flyinwall]

i have read that if they are electronicly controled you just have to change one of the resisters so it will drop the temp to a lower setting but i forget where i saw that (i hope that helps)

[KiwiBacon]

i have read that if they are electronicly controled you just have to change one of the resisters so it will drop the temp to a lower setting but i forget where i saw that (i hope that helps)

I did find an article on a ford scorpio where they did that. They actually installed a rotary switch so they could choose the settings.
Unfortunately my system appears to be too simple to do that.

[date]

Have you checked that the heater system is not still operating, thereby adding to the heat load? It could be the heater valve (if fitted) not closing properly, or if no valve, the flap not closing off the airflow to the heater core.

[KiwiBacon]

Have you checked that the heater system is not still operating, thereby adding to the heat load? It could be the heater valve (if fitted) not closing properly, or if no valve, the flap not closing off the airflow to the heater core.

Yes that's working fine. With the AC off the air out the vents is pretty much outside temp.

[Clanky]

i have read that if they are electronicly controled you just have to change one of the resisters so it will drop the temp to a lower setting but i forget where i saw that (i hope that helps)

I did find an article on a ford scorpio where they did that. They actually installed a rotary switch so they could choose the settings.
Unfortunately my system appears to be too simple to do that.

There will be a thermostat (thermistor) in your system somewhere ( Nissan sometimes calls it thermo control amp) which allows it to cycle off when it pulls down to temp. Its usually in the evaporator / fan housing somewhere. Move this to a different location out of the direct air flow or a bit further down stream to trick the system into working a bit longer. If its impossible to move you could make a shroud for it out of a piece of plastic or fruit box styrofoam to give the same effect.

Operating the AC with the ventilation system in the recirculate position can help maintain a lower temp, also window tinting can help.

[KiwiBacon]

There will be a thermostat (thermistor) in your system somewhere ( Nissan sometimes calls it thermo control amp) which allows it to cycle off when it pulls down to temp. Its usually in the evaporator / fan housing somewhere. Move this to a different location out of the direct air flow or a bit further down stream to trick the system into working a bit longer. If its impossible to move you could make a shroud for it out of a piece of plastic or fruit box styrofoam to give the same effect.

Operating the AC with the ventilation system in the recirculate position can help maintain a lower temp, also window tinting can help.

Thanks for your help. Looks like I have some quality under-dash time coming up to find this thermistor.

I do have window tinting, but the vicious UV light here has turned it from 35% black to clear in 2 years. Time for some better stuff.

[ledgend80]

what sort of fan does the car have for the engine. are there any thermo fans on the condensor. if there are not you could fit a thermo fan to the condensor to bring down the pressure in the high side therefore aiding in the cooling process

[KiwiBacon]

what sort of fan does the car have for the engine. are there any thermo fans on the condensor. if there are not you could fit a thermo fan to the condensor to bring down the pressure in the high side therefore aiding in the cooling process

A pair of factory thermo-electrics. When the AC button is on they are running flat out and doing a good job of shifting air across the condensor.

What are peoples thoughts on lagging the AC lines? No point from compressor to condensor obviously, but maybe some gain from the condensor to the evaporator where it could be soaking heat from the engine bay?

[Clanky]

Lagging is mostly only helpful to try control water condensing on the pipes.
As the cooling effect is created when the liquid under pressure turns to gas through the TX valve lagging doesnt really do that much for such a short pipe length.
If the refrigerant its getting hot the pressure goes up, and if pressure gets too high the compressor will shut off via the HP cut out switch.
So if its not cutting out I guess it not too bad.

You can also try running the ventilation fan on a slower speed, as this gives the air more time to cool down in the evaporator unit.

[KiwiBacon]

The cooling is indeed flashing the liquid to gas. But keeping the liquid at the coolest temperature must provide some improvement when engine bay temps climb.

Running the fans on low just can't provide enough cooling on the hot days. I'd like to run cooler air so I can run the fans slower. Generally I'm running on half recirc.

[KiwiBacon]

Here is the article I found on the Ford Scorpio. The owner installed a rotary switch with selectable resistance to set the cut in/out points of the thermistor on the evaporator.
http://www.fordscorpio.co.uk/acmod.htm" onclick="window.open(this.href);return false;

I still haven't been this far into the AC/Heater box to see what I can do on my car.

[KiwiBacon]

So I had a crawl around in the foot-wells and here is what I found.

A pair of wires exiting the evaporator housing on the drivers side, which when traced over to the passengers side finish in a large connected labled "Zexel 12v 2.0C" and fitted with three wires out labeled +,-,L. Clearly the thermostat.
The multimeter test shows around 13.6V output on L when the compressor is in which chops back to 0v when the compressor kicks out. Bingo

Now I just need to decide whether to give it an easy over-ride or try to reset the thermistor side of it to something more useful.

[KiwiBacon]

So I found I have to disconnect the power to the thermister amp to get a decent measurement. This is tedious.

As the temperature drops the resistance increases and at around 25 kohm the thermostat cuts out. By jumping the signal wire on the other side of the thermistor amp I can keep the AC running and drive the evaporator temperature lower. 28kohm on the thermistor is where I want it to be. Vent temps around 5C instead of 10C.

So to keep the measured cutout at 25k while keeping the actual resistance at 28k would need a parrallel resistor of:
1/Rt=1/R1+1/R2
1/R2 = 1/Rt -1/R1
1/R2 = 1/25-1/28
1/R2 = 4.28e-3
R2 = 233 kohm

Lets see if I can find one.

[KiwiBacon]

I started with an adjustable pot at 230kohm and a temperature probe in the air-vents. I keep pulling the adjustable pot down until the vent temps were cycling where I wanted them.

With 70kohm in parrallel and the fan on it's lowest setting the vent temps were cycling at 2-3C. With lower resistance they went sub-zero, but that's just asking for ice. Without the resistor they cycle around 8C. Huge difference that I'm very happy with.

The system still isn't as grunty as I'd like, being able to pull colder temperatures at higher fan speeds would be ideal. But for now it's a big improvement.
Now I just need to buy a fixed resistor and wire it in more or less permanently.

I keep thinking how the most user-friendly AC system I have is in my old rangerover. It has an AC thermostat right underneath the AC fan control. Set it where you want it and leave it. Why don't modern cars?

[Clanky]

Nice work
Yes my old AC back in 82 had a variable temp selection pot on the dash. I just left it on max cold and life was good.
Sub zero temp on the evap is not so bad as long as you have constant air flow and the humidity is not too high.
Worst that can happen is the AC wont be as cold and you will eventually see a snowman in the passengers footwell
Same thing can happen if the evap fan stops blowing air on a standard unit.

[KiwiBacon]

After the test drive I think it needs a switch. The closest resistor I could cobble together was 62 kOhm and that had air getting as low as 1C out the vents and even as low as 3C when driving at 100km/h with the fans on 2 and 25C air coming in. I live in a very dry place, but any rain or fog would turn that into a popsicle pretty quick.

At the moment it's a case of reach into the passengers footwell, unclip a cover and unplug the resistor wire to bring it back to 10C vent temps. It works but I'll come up with a switchable solution later on.

[Clanky]

again, nice work
Another thought is to add a potentiometer into the loop then you can adjust from normal to cold depending on the day

[KiwiBacon]

again, nice work
Another thought is to add a potentiometer into the loop then you can adjust from normal to cold depending on the day

Thanks. I'm pretty stoked with how this turned out.
I did consider the pot, but it's harder to know the position than simple 1 or 2 clicks of a switch. I'm running out of locations for extra switches in my work car.

[Guy]

There will be a thermostat (thermistor) in your system somewhere ( Nissan sometimes calls it thermo control amp) which allows it to cycle off when it pulls down to temp. Its usually in the evaporator / fan housing somewhere. Move this to a different location out of the direct air flow or a bit further down stream to trick the system into working a bit longer. If its impossible to move you could make a shroud for it out of a piece of plastic or fruit box styrofoam to give the same effect.

Operating the AC with the ventilation system in the recirculate position can help maintain a lower temp, also window tinting can help.

Thanks for your help. Looks like I have some quality under-dash time coming up to find this thermistor.

I do have window tinting, but the vicious UV light here has turned it from 35% black to clear in 2 years. Time for some better stuff.

definately ... we have 35% on my wifes car and the UV can get pretty high .. especially on 45C days ... has been in good order for the past three or 4 years. ( we purchased two identical booster seats for my son, one in the wifes car one in mine ... the one iin my wifes car is still black .. the one in mine a dusty kind of grey)

[KiwiBacon]

I've got a local guy happy to retint it with better film. On the proviso that I have to remove all the old stuff. A real mess apparently. But I've heard a steamer helps.

[RAY185]

But I've heard a steamer helps.

Yeah most things are easier after a good shit but it's still a bastard of a job.

[KiwiBacon]

Finally finished this job.

I have a four position rotary knob to the left of the steering wheel. This is wired into the thermistor on the evaporator and acts as a temperature selector.
Setting 0 is no connection and gives factory cool air. Roughly 11C today.
Setting 1 has 300k ohm in parrallel and today was producing air at around 8C
Setting 2 has 110k ohm in parrallel and today was producing air at around 4C
Setting 3 has 37k ohm and today was producing air sub-zero.

Just one last thing to do, laser etch the surround on the knob to say "AC TEMP" and STD, 1,2,3 or something like that (haven't decided yet).

[Clanky]

nice work, and sounds professional enough to sell as a kit on Ebay

[RED60]

Finally finished this job.

I have a four position rotary knob to the left of the steering wheel. This is wired into the thermistor on the evaporator and acts as a temperature selector.
Setting 0 is no connection and gives factory cool air. Roughly 11C today.
Setting 1 has 300k ohm in parrallel and today was producing air at around 8C
Setting 2 has 110k ohm in parrallel and today was producing air at around 4C
Setting 3 has 37k ohm and today was producing air sub-zero.

Just one last thing to do, laser etch the surround on the knob to say "AC TEMP" and STD, 1,2,3 or something like that (haven't decided yet).

Perhaps...... STD, -1,-2,-3...... just for fun

[sw1]

But I've heard a steamer helps.

Yeah most things are easier after a good shit but it's still a bastard of a job.

lol

On the proviso that I have to remove all the old stuff. A real mess apparently

I had my vehicle tinted on saturday (2 days ago), I witnessed & chatted to the professional tinter whilst he did the last window - both pulling the old tint off and putting the new stuff on. To remove the old tint he used a scraper with a new blade to lift an edge of the old tint, then carefully pulled nearly the whole piece off in one go. Once the piece of old tint was off, the window was still covered with old adhesive. He then sprayed the window with baby shampoo and water from a squirty bottle and used the scapper, with new blade, to scape the old adhesive off in vertical down strokes.

The words from the professional tinter were: a new blade in the scraper is key and with the soapy water on the window you will never scratch it.

Good luck.

[KiwiBacon]

Allegedly if you are careful with the steamer then all the adhesive comes off with the old tint. I haven't tried it yet, far more worthwhile things to do.

[Hekta]

There's some pretty damn cool tech in this thread
You've certainly gone to a lot of effort KiwiBacon, but looks like it's paid off.

[KiwiBacon]

There's some pretty damn cool tech in this thread
You've certainly gone to a lot of effort KiwiBacon, but looks like it's paid off.

Thanks. It's a mod that's continued to work exactly as needed. Get in the car, crank it to cold and back it off when it becomes unbearable.