Evaporator Thermistor
 

Any advice on modifying thermistor; sucess stories, failures, etc?

thermistor
 

is either a typo or a part i am not familiar with.

tom w

What car and year?
 

Are you aware of :

http://pages.prodigy.net/jforgione/MB_S500.html check item 18, It's something kind of similar to what I believe you are speaking of.

I did read your post and link about Ford Scorpio AC modifications. Sounded just like what I wish my W140 had. But , where on my 95 S420 is that thermister located. Likely way down in the bowels of the evaporator housing. Anyone know which wires (colors), where they come out, and where they go, and what relays (switching on-off the compressor) they control?

Good luck,
DanielW

a thermistor is a resistor designed to maximize the resistance change with temperature

I know there is at least one who has adapted his ets (evaporator temperature sensor) as I read his thread of how he was unfortunate/amazed to make a block of ice. Didn't hurt his system, but it has the potential to starve the compressor (not good) so it should be "tuned" carefully. I believe he had it set (ets) at 0 degrees and was going to raise it a bit. ASAMOF what is the compressor cut out temperature on a 201 ets?

I know it's not hard to adjust; I'm just looking for what size resistor for w201 ets. He's close.

Y'know...you ought to try and understand air conditioning before you attempt to modify it. How, exactly, will the compressor 'starve'?

Well, perhaps starve is not the correct term..but if the evaporator is frozen, lets say it's because you've modified the Evap Temp Sensor too low of a value. the TXV is closed yet the compressor keeps running putting a lot of stress on it.

common dude; why so rude?
 

If we knew everything, we wouldn't need a site like this. I do have an engineering background. It's my nature to make things better; as it as been said on another ACforum; "AC system performance is dependant on the vehicle it's in" some vehicles run better on a different system. I'm looking to make a hybrid, and have found out that Bentleys have done this in the past. Anyway, here's some AC info for you Moneypit......the author uses the term "starve" I believe. Maybe you should email him.



http://www.asashop.org/autoinc/march2003/mech.cfm

First, why would anyone modify a txv to close completely? Can that even be done? Aren't you playing around trying to increase refrigerant flow through the evaporator, and not limit it?
Second, a 'frozen' evaporator refers to ice on the outside. Refrigerant is still happily circulating inside the system.
Which brings us to an obvious limit in the A/C system. The evaporator. If the evaporator is allowed to reach a temperature lower than 32F, the moisture condensing out of the air will freeze on the evaporator instead of dripping off and draining away. Therefore, the evaporator cannot be colder than 32F. At least, not if you want the system to provide cold air. 35–40F is the practical limit. All the valve and thermistor twiddling in the world will not change this. If an A/C system does not maintain the evaporator temperature below 40 degrees and above 32 degrees, improvements can be made. But only until the correct evaporator temperature is achieved.

Which means you might know something about engineering. Apparently, it does not mean that you know you should understand what you're dealing with before you try to change it.
Or not. I've hardly the time to go about finding and correcting every last misconception on the internet. I'll settle for the ones that find me.

Remember, we're talking about modifying the ets to allow the evaporator to get colder than spec....therefore the evaporator will freeze literally on the outside. The txv is still operating; it senses cold so it closes....no refridgerant going through. You now have a high side pressure increasing with very little or null low side vapor getting to the compressor. the ford scorpio spec is -2 c on it's evaporator....I want mine lower too.

Here's another thread....

BTW, I think someone had mentioned that the reason that car companies don't utilize more TXV is because of cost....I don't by that in today's economy. Competition is fierce and a main selling factor of the car is it's air conditioning. That comment about cost would be true if we assume both systems employed in that particular car performed the same. That's the right business choice.

I believe that auto engineers use the best system for their car today and it's based on passenger comfort. The argument can be made that car companies don't use a "hybrid" system 'cause it would add another $125.00 to the vehicle when they can get a max cooling cheaper with a FOT....that would make sense too. the only company I know of to use the hybrid is Bentley.
there is a lot of resistance to make things better here when we talk about AC. Replacing the original is good, easy, been there done that, if your benz performs well in your climate. Well, not everyone is that fortunate.

http://www.autoacforum.com/messageview.cfm?catid=2&threadid=14142&FTVAR_MSGDBTABLE=

right, I understand fluid will still be happily going through the evaporator....hence the accumulator is needed. right, the txv would not be completely closed as this would be per my modification/adjustment too (low superheat). I use the term closed when I should have used "closes but not completely because it can't."

I do try to understand and get all points of view before I begin something...I'm conservative by nature (majority engineering behavior).

It appears that you know everthing and wait for stuff to find you right?
Hence you won't look at the thread. Bliss.....Once again, your AC might be fantastic or just great in your climate and you're happy as a lark. Come on down to Fla. for a while. I agree, the evaporator is the limiting factor..I'm trying to do something with mine. Please don't condemn me for trying.

The main difference between a SEER 10 and 12 units in a home system is a TXV. Since I purchased my last one for $20, you'd think market forces would prevail and increased production rates would make the SEER 12 units come down to the same cost.
Hasn't happened- industry has fought it and lobbied our gov to continue making SEER 10 units.

Stupid!

Michael

In addition
 

You can run the evaporator several degrees below freezing if your car is in a hot climate. The warm air across the fins will keep the evap from freezing. Surely, you've been in a car with extremely cold vents haven't you? It is my belief that foreign cars and maybe ford incorporate the outside temp as a switch/relay that adjusts the evaporator temp sensor to cut the compressor out at a lower, below freezing temperature in the evaporator.

I meant to say low side pressure switch, not ets for the asain and ford. Yes the switch is fixed, but their maybe something in-line resistor adjustment from computer management.