SabrToothSqrl

I'm not sure what water has to do with the compressor, but yes, if you change the pressure or purity, you can change the 'freezing' temperature. There are actually 15 stages of 'ice'.

Ice - Wikipedia, the free encyclopedia

Water phase diagram

My Jeep and my Wife's car both let you run the A/C compressor at any temp. (as did my 1995 Tahoe)

Actually, I'd like the Tahoe's Auto mode to NOT run the A/C until it's at least 50-60 out.

If it's 60 out, and I want the car at 72, I don't really need to use the A/C. (Yes I know it works as a dehumidifier) But I'll keep my 1MPG lol!


But, these systems are R-134a, which "freezes" (actually melts at)

-153.9°F (-103.3°C)
1,1,1,2-Tetrafluoroethane, Melting point (that's really freaking cold)!

https://www.google.com/search?q=r134...ient=firefox-a

so... I'm going to assume you mean the evaporator, freezing up?

That's actually quite common and not an issue, other than the reduced performance if it was a block of ice.

Not running the compressor during cold weather may extend it's life due to simply not running. But most vehicles run the A/C when the selector **** is on defrost any way. Even in the dead cold of winter. The light may not come on, but select it on a car, then pop the hood and see if the compressor is running .

Most manuals state this, and state to not use defrost when not needed, as it runs the A/C compressor.

73shark

Two reasons to run compressor on Defrost, one to defog the W/S and two to keep seals lubricated.

If they run the compressor below ~38*, then they are either somehow bypassing the evaporator or accepting it turning in to a block of ice. But I haven't checked other mfg so will admit to not knowing what they do.

Wife just ordered a new Sequoia, so will see how Toyota does it. BTW, her 2004 Tahoe A/C doesn't run the compressor below ~38*

SabrToothSqrl

what is the path of air from the outside to the cabin?

My guess is it goes to the heater core first.

So, if it's 30 outside, the air gets first heated to let's say 80, then gets cooled by the evaporator.

So, the evaporator never sees freezing temps (Assuming the engine is warm).

or is it the other way? evaporator first, then heater core?


hmmmm.....

73shark

Evap then heater core, which is why it helps defrost because it drys the air and then when it's heated up, the RH is even lower.

SabrToothSqrl

if the evap is first, you'd think it would freeze up more often.

73shark

That's why A/C systems have controls to prevent the evap from icing.

TWard

It has been in the 80's the last few days and the AC blinks 3 times and won't engage. I get the low temp lock out- have that with my 09 Buick. So it's not a low temp that's keeping it from engaging. What's next? Bad relay, low refrigerant, bad temp sensor?

Your thoughts, ladies and gentlemen?

07 Burb LTZ, 5.3 flex, 105,000, 3rd owner, new to me (driving it a week).

73shark

First check the refrigerant level.

BW56

My AC works year round in Phoenix.

SabrToothSqrl

I wish I was in phoenix, more specifically, Lake Havasu City...

I'd check the fuses and coolant level (pressure).

my '95 Tahoe would kick on/off when the coolant was low... it had a slow leak where I'd just add a can every few weeks... then I sold it.

I miss my '95 Tahoe... I liked that Truck.