Blower Motor Upgrades?

[bfloyd]

Correct me if I'm wrong, but the motor we want turns counter-clockwise Correct? Looking at my receipt, I ended up getting the blower motor for a 1980 Chevy Monza.
http://www.autozone.com/cooling-heat...44_0_6648_5281
It turns counter-clockwise, all of the screw holes are in the exact same spot, and the electrical connection is identical. I just thought changing out the 36 year old motor would make a huge difference, instead it's just exactly as it was before.

I'd just like the same volume of air I get out of my 2004 F150.

[David T]

If you move the air too fast over the coil it doesn't have enough time over the coil and you get less of a temperature drop, not more. Make sure the hole in the forward firewall. in front of the driver is blocked. The original foam falls out. Make sure the ductwork inside the doors are sealed and you are not losing air inside the doors. Make sure the boot for the center dash ducts is fitted correctly and not blocking or leaking. Make sure all of the ducts and actuators are working and move correctly. Make sure the mode switch isn't hissing. The biggest problem as I see it is you cannot aim the vents well and blow on the driver and passenger. There have been efforts in the past to make deflectors so the door vents can blow on the occupants. Make sure the fan motor is rotating in the correct direction. Some cross/overs run "backwards" and while they do move air, it is a fraction of the necessary amount. Park in the shade. Try MAX for initial cool-down. Make sure the compressor is cycling correctly. If it isn't you may have too much or not enough refrigerant and the evap coil can freeze, blocking airflow.

[Jason]

If you move the air too fast over the coil it doesn't have enough time over the coil and you get less of a temperature drop, not more.

Isn't that only true if you're trying to cool outside air? If you're recirculating air then I would think in terms of how fast you can remove heat from the cabin more air flow would always be better, at least up to the max capacity of the rest of the AC system, and then beyond that things would stay the same. Unless keeping the evaporator too hot would cause pressure problems in the refrigerant.

[Jason]

So, if you did want to increase air flow using the same motor but different fan design, how would you change the design? I can pretty easily make new fans. Just for fun I have one printing now with twice the blade area.
fan.jpgfanprint.jpg
But I have no idea if that's going to increase air flow or not.

[David T]

Transferring heat from a moving stream of air to a coil (and then to the refrigerant) requires the air to be in contact with the coil (the fins and metal) for a finite amount of time. You must transfer the heat from the mass of air to the mass of the coil. It doesn't happen instantaneously. The longer the air is in contact, the more heat can be transferred. Yes, you will get more air over the coil but the temperature change (delta T) is less. The curve is going down as the airflow goes up. You quickly reach a point of diminishing returns. At infinite airflow you get 0 delta T. Noise also increases as you increase airflow. Another factor is comfort. Too much air blowing in the cabin will become uncomfortable. So there is an upper limit to how much air you want to move. A normal Delorean with the cabin fan on high is about as much air as you should need. If you aren't getting a really good airflow on high, check the fan motor rotation, the actuators are moving the doors appropriately, and you aren't losing air from leaks or blockages.

[Josh]

Jason, I am very interested to hear about the results of your testing. Very cool that you are producing your own squirrel cage!

[Jason]

Transferring heat from a moving stream of air to a coil (and then to the refrigerant) requires the air to be in contact with the coil (the fins and metal) for a finite amount of time. You must transfer the heat from the mass of air to the mass of the coil. It doesn't happen instantaneously. The longer the air is in contact, the more heat can be transferred. Yes, you will get more air over the coil but the temperature change (delta T) is less. The curve is going down as the airflow goes up. You quickly reach a point of diminishing returns. At infinite airflow you get 0 delta T. Noise also increases as you increase airflow. Another factor is comfort. Too much air blowing in the cabin will become uncomfortable. So there is an upper limit to how much air you want to move. A normal Delorean with the cabin fan on high is about as much air as you should need. If you aren't getting a really good airflow on high, check the fan motor rotation, the actuators are moving the doors appropriately, and you aren't losing air from leaks or blockages.

But in the case of recirculating air the air repeats the contact with the evaporator more often. While I haven't worked through the math, I'm pretty sure that in the recirculating case if you take the limit as the air flow goes to infinity it reduces to the case where all the cabin air is in contact with the evaporator all the time. Which is different from the non-recirculating case where you don't get a temperature drop because each bit of air is only in contact with the evaporator for one infinitely small instance of time.

[David T]

Recirculating helps, that is why there is a recirc mode. But you still have a lower Delta T because of the time any particular particle is in contact with the coil. Bottom line, to high an airflow is not good.

[rickjames8]

Recirculating helps, that is why there is a recirc mode. But you still have a lower Delta T because of the time any particular particle is in contact with the coil. Bottom line, to high an airflow is not good.

I have been wondering this. I don't see a recirc/fresh switch like on most cars. How do I select if the air comes in from outside, or gets recirculated?

[nkemp]

I have been wondering this. I don't see a recirc/fresh switch like on most cars. How do I select if the air comes in from outside, or gets recirculated?

Max recirculates interior air (it does bring in some fresh air. 15%?)
Norm uses outside air

When the car has been sitting and is very hot inside, run on NORM for a while. Outside air is probably cooler so the AC cooling increases (the load is decreased). Once the car has cooled for a while, use MAX for maximum cooling. MAX recools interior air which should be cooler than outside. Humidity is also a factor. If outside air is very humid, even though the inside air is the same temp or a bit higher, then it is better to use the inside air (MAX). Humid air has a lot more energy in it and is a greater load on the AC.

If you really want to know more or to compare humidity load and temperature variations, use the psychrometric chart. Here is a description:https://sustainabilityworkshop.autod...ometric-charts