Is there a "recirc" for heat?

[Doubletrouble]

 On the dash you can place the a/c on max and it recirculates the air in the cab to continuously cool the same air making the cab cooler in the summer heat. 

 Is there a recirc setting that does the same for heat in the winter? Or do we have to set it on max a/c setting which blows the hot air from the main vents?

 Thought it might be useful on the really cold days. 

[That Guy]

On the 12v's you have 4 fan speeds with the a/c comp and 4 without. The vent controls are agnostic with respect to the the fan controls. So you would simply set it to non a/c recirc.

 

 I'm unsure on the 24v's as they don't have a dedicated a/c button or quadrant of control I know of. Since It doesn't have that I assume the computer does the thinking for the a/c compressor and turns it on when it deems necessary. Maybe set it to max a/c and full heat and see if it cycles the clutch.

[JAG1]

Good question,

[Tractorman]

4 hours ago, Doubletrouble said:

 Is there a recirc setting that does the same for heat in the winter? Or do we have to set it on max a/c setting which blows the hot air from the main vents?

 Thought it might be useful on the really cold days

 

It does seem like a good idea, but there is one thing you are overlooking.  That nice warm air will never exit the cabin, consequently the air will continue to pick up moisture (from wet clothes, wet shoes, your own breath, etc.) and that moisture will begin to condense on your cold windshield and side windows.  You may be warm and toasty - you just won't be able to see.

 

By always bringing in outside air into the cabin during the heat or defrost modes, the added moisture to the air will always be exiting the cabin while fresh dry air is entering.  

 

- John

[dripley]

I can set mine to recirc and turn the temp knob to hot and it blows hot air.

What the AC is doing during this I dont know. Never use that way just tried it see a good while back. Have it set there now while sitting in the parking lot here at CFA.

Edited December 16, 2020 by dripley

[Doubletrouble]

 I tried it yesterday sitting in a parking lot as well. It seemed warmer, didn't have a thermometer with me at the time though. Idk, I was just curious.

[IBMobile]

2 hours ago, dripley said:

I can set mine to recirc and turn the temp knob to hot and it blows hot air.

What the AC is doing during this I dont know. Never use that way just tried it see a good while back. Have it set there now while sitting in the parking lot here at CFA.

The AC compressor is on and the recirculating air is being dehumidified.   

[Doubletrouble]

@Tractorman, I see your reasoning here but, I have had vehicles in the past with no a/c from the factory. Yes, you would do best to crack a window to let the air flow better but you could still see. 

 I do appreciate having a/c even in the winter for the defogging of inside of the glass for sure.

[Tractorman]

5 hours ago, IBMobile said:

The AC compressor is on and the recirculating air is being dehumidified.

 

This works fine if the outside air temperature is well above freezing.  Once the outside temperature falls to freezing or below, the AC compressor cycles less and less, finally to the point it does not cycle at all if the outside temperature falls well below freezing.  This is due to the low saturation pressure of the refrigerant.  The recirculating heated air will warm raise the saturation pressure of the refrigerant somewhat, but the exposure of the condenser being first in line to the cold outside air will cool the refrigerant so rapidly that the saturation pressure will likely be too low to cycle the compressor.  Note the saturation pressure of the refrigerant at 30 degrees in the chart below:

 

 

 

A few years ago when my heater core was leaking, my side windows would begin fogging when it dropped to around 40 degrees outside.  The fogging would creep around to the edges of the windshield and slowly worsen.  With defrost selected he compressor was cycling, but the on cycles were short and the off cycle were long  - not giving enough time on to dry the outside air further.  With the added moisture from the coolant leak the windows would fog.  I even tried setting the controls to AC recirc, but it was worse as I expected it would be.   (Note, I  have a refrigerant recovery system, so I had the correct weight of refrigerant in the system).

 

At that time I needed to go on a long trip over the Cascade Mountains during the winter.  I knew that I would have window fogging problems.  I rigged a momentary switch that I could hold in my hand inside the cab to bypass the low pressure switch so I could run the AC compressor for as long as I chose.  Once I started climbing the pass the outside temperature fell to below 40 degrees (raining and foggy) and my windows started to fog.  I depressed the switch for 2 or 3 minutes followed by a release time of one minute or so and the windows cleared right up.  If I were to have done this for a long period of time I am sure that the evaporator core would have started to freeze up, but it got me over the pass with great visibility.  The reason I mention this trip is because it shows the limitations of the AC systems in our trucks.  

 

@Doubletrouble, your idea may work for you, but you could have window fogging under certain conditions for the reasons mentioned above.  A lot will depend on the climate where you live and what the outside conditions are when you use the recirc function for heating.  I know that years ago a friend of mine had a Toyota that would allow air recirculation in the cab with heat and no AC.  The friend complained that sometimes the windows would fog during the cold season.  He told me that he used the recirc all of the time.  I suggested the he turn the recirc function off and go to defrost mode or defrost / floor mode.  He did and his fogging problems disappeared (literally - ha! ha!).

 

- John

[Doubletrouble]

 And @Tractorman you are correct. Say your outside, have rain/snow on your clothes or shoes whatever. You will have fogging on the inside due to the excess moisture in the cab. I experienced this many times for one reason or another. Not going to dispute it. I was just thinking that on an exceptionally cold day, if the option was there it could be beneficial to at least get the cab warm then switch back to normal heating mode is all. With the controls in an '01 such as mine there is no clear way to do so, that's why I asked.

@Tractorman

Edited December 16, 2020 by Doubletrouble
Double post

[dripley]

D

Well dammit is all I can say. It amazes still of all the in and outs of things and what folks know about around here. Sometimes its above my little pea brain.

My education continues.

[Tractorman]

4 hours ago, Doubletrouble said:

I was just thinking that on an exceptionally cold day, if the option was there it could be beneficial to at least get the cab warm then switch back to normal heating mode is all.

 

If you are considering that an exceptionally cold is a below freezing day, then I would think that the interior of the truck could be warmed faster in the recirc mode without fogging windows as long as the interior of the cab was dry.  Of course the heat would be coming out of the dash vents, but who cares if you are not in the truck.  Then, like you say, you can take it out of the recirc mode when you get in the truck to drive away.   I will have to try that sometime in the near future.  I think you might be on to something.

 

- John

[JAG1]

So you guys are sayin' put the top selector knob on floor and dash vents (next one just above the air conditioning) and then turn the bottom knob all the way to warm? This closes off the outside air to recirculate. Is that right?

Edited December 17, 2020 by JAG1

[dripley]

Turn it to max ac. Then turn the temp knob to hot.

[Tractorman]

1 hour ago, JAG1 said:

So you guys are sayin' put the top selector knob on floor and dash vents (next one just above the air conditioning) and then turn the bottom knob all the way to warm? This closes off the outside air to recirculate. Is that right?

 

Not quite.  Set the top selector to Max AC.  This puts it into the recirculation mode.  All other selections bring in outside air.  

 

I see @dripleyposted while I was writing.

 

- John

 

 

[JAG1]

5 hours ago, Tractorman said:

 

Not quite.  Set the top selector to Max AC.  This puts it into the recirculation mode.  All other selections bring in outside air.  

 

I see @dripleyposted while I was writing.

 

- John

 

 

He always does that never waits his turn.......

 

John I know the air conditioning works on the floor and dash vent combo setting also if the bottom knob is on cold. So just to make sure; you say we need to put on Max A/C to close off the outside air is that right? And then turn bottom knob to warm.

 

Thanks in advance.

Edited December 18, 2020 by JAG1

[dripley]

5 hours ago, Tractorman said:

 

 

I see @dripleyposted while I was writing.

 

- John

 

 

Wise minds think alike, John.

 

Dave

5 minutes ago, JAG1 said:

He always does that never waits his turn.......

 

John I know the air conditioning works on the floor and dash vent combo setting also if the bottom knob is on cold. So just to make sure; you say we need to put on Max A/C to close off the outside air is that right? And then turn bottom knob to warm.

 

Thanks in advance.

 Yes. Max ac is the only recirc mode. Ha Ha, did it again.

 

Chicken 

Edited December 18, 2020 by dripley

[Tractorman]

2 hours ago, JAG1 said:

He always does that never waits his turn.......

 

You're on the Board of Directors - can't you make him wait?

 

In my opinion the "Max AC" label is a poor choice of words to describe the function that is being performed.  How about calling it "Recirc"? -  since that is what it does.  After all, that is what most other auto manufacturers call it.

 

John

[dripley]

Itmdoes max ac but i believe that it has a little recirc arrow on it too.

[Dieselfuture]

6 minutes ago, Tractorman said:

 

You're on the Board of Directors - can't you make him wait?

 

In my opinion the "Max AC" label is a poor choice of words to describe the function that is being performed.  How about calling it "Recirc"? -  since that is what it does.  After all, that is what most other auto manufacturers call it.

 

John

Make sense, the only problem is it still turns ac on. Now if you're like me and put a toggle switch on to shut off the ac compressor then it becomes a recirc.