Updated Lotus AC thermostat question - LotusTalk - The Lotus Cars Community
 
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post #1 of 20 (permalink) Old 08-29-2018, 03:36 PM Thread Starter
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Updated Lotus AC thermostat question

Anyone up for a little R&D?

I would like to see what the vent temps are on a later model Elise with the updated AC thermostat.

Ideally, It would be moderately hot[say in the 80's]

Steady state after the cabin is pulled down to temp

highway speed

oh, and with a reasonably fast acting temperature sender, like a thermocouple

Did I mention I was fussy?

I am trying to do some thinking on the AC system,I am curious why we cannot get vent temps as low as some cars, the system is capable, so I am curious of Lotus' fix lowered or raised the vent temps
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post #2 of 20 (permalink) Old 09-15-2018, 09:17 PM
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My experience is that the Elise A/C can only lower the intake air 20 deg F. The thermostat only allows it to be productive longer because of not "freezing" up the system. After all, how many days of 95+ weather does UK have?
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post #3 of 20 (permalink) Old 09-16-2018, 04:22 AM Thread Starter
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Well, the Elise AC can do whatever you tell it to, but yes, it will ice up. I mean, I can make it produce any temp air I want, why it freezes up when other cars systems don't is a bit of a mystery. The TXV 'should' stop it.

With the stock old style thermostat I get air temps in the mid 40's with a cabin temp of low 70's and outside temps in the 90's. I have significantly improved airflow, but if I try to lower the air temp it ices, when really, it shouldn't.

I'm just wondering if the newer thermostat raises the air temp[which I would consider worthless] or is jsut more accurate or something

If I had nothign better to do I would expirement with different TXVs, because the TXV should really stop it from icing.
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post #4 of 20 (permalink) Old 09-16-2018, 08:01 AM
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The new electronic sensor reacts more quickly to cycle the ac compressor to prevent evaporator icing. My discharge air temp is 42 degrees here in south Florida.
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post #5 of 20 (permalink) Old 09-16-2018, 08:17 AM Thread Starter
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ahhh, interesting

With the old thermostat, I will hit, depending on conditions, 44-46 degrees, then it will rise to ~52 degrees before turning back on.

the only annoyance is that you get that 'damp' smell like my AC isn't working, for a few seconds. When it is over 90, it is rare as it is working pretty hard and it doesn't hit the thermostat. When it is 80 it cycles regularly and gets annoying.

bofusric, do you have a fast enough thermometer to tell me what the temp spread is?
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post #6 of 20 (permalink) Old 09-16-2018, 12:44 PM
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I now recognize the damp/humid smell when my AC decides to stop cooling. I previously did not associate it with the new thermostat.

1) Are you using a metal thermometer stuck into vent to read 42deg? I use a laser thermometer and never got a number that low.

2) Do you have a hard or soft top on while using A/C? Soft top with touring (my config)?

3) Are you in recycle mode with vents set to dash, wind screen or floor? If the later does the temp change when you exclude the floor vents?

Thanks for sharing. I'll try to get similar readings when I know your config.
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post #7 of 20 (permalink) Old 09-16-2018, 01:58 PM Thread Starter
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Personally I use a DVM with a K thermocouple.

The dash vents are the only thing worth using, I have my floor vents permanently stuck open for the extra flow.

I have run my AC with the soft top on, I think sun load may have an effect, but not much. Mines an Exige, so only had the soft top on a few times
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post #8 of 20 (permalink) Old 09-17-2018, 01:38 PM
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I have a digital metal probe temp sensor that I used, I also have a laser. I will try both in a few days. This is with touring top on. I now have the hardtop and will check this way. I always use face vents only. I do have a tint on my windshield that helps with the sun load and with off gassing of the dash. I have never used recycle mode because I never feel or hear a difference and have the blocking plates removed in the footwell for extra airflow.
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post #9 of 20 (permalink) Old 09-18-2018, 03:18 PM
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The upgraded electronic thermocouple is a must.
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post #10 of 20 (permalink) Old 09-19-2018, 12:45 PM
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ac thermostat

Here are the readings from my car today using a laser and digital thermometer. As you can see it was 88 degrees in Lauderdale-by-the Sea at 3:30 today. The 36 degree was laser thermometer pointing at outer ac vent, the 26.9 degree was laser thermometer pointed at internal ac duct, the 46.5 degree was digital. I think I would trust the laser thermometer more. These pics were taken at idle, the temp gets colder when driving. I would definitely recommend the electronic thermistor, without it my evaporator used to freeze up after driving about an hour. the digital may need to be calibrated.
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post #11 of 20 (permalink) Old 09-19-2018, 09:50 PM
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Quote:
Originally Posted by exigegus View Post

I would like to see what the vent temps are on a later model Elise with the updated AC thermostat.
From what model year? I have an 07 Exige and no compliants. Pretty cold air blowing from vents.

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post #12 of 20 (permalink) Old 09-20-2018, 03:36 AM Thread Starter
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Some 07's have the old thermostat, some the new.

'pretty cold' is not exactly what i was looking for.....

limited airflow, I think, hinders the performance that most,
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post #13 of 20 (permalink) Old 09-20-2018, 05:51 AM
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Quote:
Originally Posted by bofusric View Post
Here are the readings from my car today using a laser and digital thermometer. As you can see it was 88 degrees in Lauderdale-by-the Sea at 3:30 today. The 36 degree was laser thermometer pointing at outer ac vent, the 26.9 degree was laser thermometer pointed at internal ac duct, the 46.5 degree was digital. I think I would trust the laser thermometer more. These pics were taken at idle, the temp gets colder when driving. I would definitely recommend the electronic thermistor, without it my evaporator used to freeze up after driving about an hour. the digital may need to be calibrated.
An IR thermometer cannot be trusted at all unless you have set the emissivity correctly. A plastic piece at 27F and an aluminum piece at 27F will both radiate heat differently, so the thermometer must be manually set up for each one differently.

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post #14 of 20 (permalink) Old 09-20-2018, 07:27 AM Thread Starter
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And anything with a 'heavy ' probe does not react fast enough. I can watch my thermocouple probe tick upwards and downwards in real time. Tehre is still some thermal mass, but not compared to the hardware store thermometer I use to measure cabin temp. That thermometer will basically give me an average temp, you cannot see the thermostat kick out. If the on/off temps are like 52/47 it will show you 49 +- 1
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post #15 of 20 (permalink) Old 09-20-2018, 11:55 AM
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The IR thermometer readings were taken from the outer plastic vent flap and the inner plastic ac duct about 3 inches behind vent assembly. If you car still has the old style ac thermostat I would change it to the electronic style, its one of the best updates ever.
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post #16 of 20 (permalink) Old 09-20-2018, 02:07 PM
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Arrow Cold as Hell?

I don't have the exact numbers or temps, but in the past my 05 stock A/C unit would ice up every 2 or so years on very long drives. I took one long drive this year with the new electronic module installed and it did not ice up. Generally, the how cold does it feel, temps are way colder this year in general I have noticed, probably due to the electronic modules efficiency. This is coming from a car that never has the top on, so the A/C really struggles to work.

You definitely need to do the other mods too. One other mod I did was wrap the flex tube to the hard tube in the front clam with some Aluminum duct seal tape. There was a VERY minor air leak around the rubber tube. By wrapping it up, the air velocity in the cabin drastically increased, which was really needed for a car with the top off.

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post #17 of 20 (permalink) Old 09-20-2018, 06:20 PM
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Ara (shay2nak) --

Per the instructions that came with the new thermostat (A. C. Thermostat Kit, p/n A120P0149S), that I had installed in my 2005 Elise, "The electronic thermostat was introduced on factory build at approx. February 2007".

I think the new thermostat (along with switching to the "Hose, heater to plenum, insulated", p/n A124P0025F) made a big difference. This updated hose was fitted started with the '07 model year and can be retrofitted to the earlier cars.

I have not looked into using the "Hose Insulation Sleeve, heater to plenum", p/n A120P0161F that was apparently fitted to the "Gulf states" cars. If anyone has, how well did i work?

-- Mike
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post #18 of 20 (permalink) Old 09-21-2018, 05:53 AM
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I wasn't aware about that updated hose. I will pick that up next time I need to order parts.. thanks for the heads up.


I did however wrap that hose with foil back insulated wrap along with insulating the covers coming from the radiator and blocking off the inlet that leads that hose to the cabin made a nice improvement here in South Florida.


I've done most of the steps in this link short of insulating the interior and it has really made a noticeable difference.

https://www.scribd.com/document/21519645/Improved-Ac
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post #19 of 20 (permalink) Old 09-21-2018, 03:33 PM
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The electronic thermostat will not deliver colder air temperatures.
What it will do, is more accurately control the compressor, thereby alleaveating the freezing up of the evaporator coil.
To increase interior cooling, the best thing to do is insulate.
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post #20 of 20 (permalink) Old 09-22-2018, 07:21 AM Thread Starter
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Quote:
Originally Posted by SirLotus View Post
The electronic thermostat will not deliver colder air temperatures.
What it will do, is more accurately control the compressor, thereby alleviating the freezing up of the evaporator coil.
To increase interior cooling, the best thing to do is insulate.
Michael
The point of my OP was to try to determine what air temps it will deliver.

Actually, i think that while insulation is useful, increasing the airflow is key. Using the old style thermostat I have no issues with icing. I was playing with an adjustable style, but it is not located properly and did allow icing.

I am also wondering if the TXV is not properly spec'ed, but that is way above my pay grade
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