2nd Gen Cummins heater temp differences between trucks

[Tractorman]

6 hours ago, 01_Cummins_4x4 said:

I'm getting 150° temp out the dash vents on full heat and highest fan setting. That's like 50° hotter than it was before.

 

I think you won.

 

- John

[JAG1]

One more thing worth mentioning about the rodent and debri screens under the cowel, MoparMan taught me to also block the round hole on the passenger side... is almost straight down below the hood hinge. It's about 2 or 3 inches in diameter and can be reached with one arm down inside the fender. I simply rolled up enough screen to stuff the hole full and get it tight. You have to fold the screen and roll it up so there aren't any sharp wires to stab your finger tips while stuffing it tight in there. It works good and I know you have to do it because I had the screens like IBMobile but, a mouse still got into my heating and AC plenum under the dash. I had to trap the little bugger before I could block off the hole because if he died in there it would smell like something you never want to own. I took me two tries to get that mouse, was very skilled at taking the peanut butter and not setting off the trap. Once I got him he was mad as hell. Must of had it good in my heater plenum. I had to clean the nest out which was in the blower motor squirrel cage fan. I simply bought a new motor and fan to take care of it.

[Mopar1973Man]

12 hours ago, 01_Cummins_4x4 said:

I finally got my new adjustable control arms and Thuren front lift springs installed. I removed the front lift spacers to get a smoother ride out of the front suspension. 

 

I was able to drive it and when it's fully warmed up, I'm getting 150° temp out the dash vents on full heat and highest fan setting. That's like 50° hotter than it was before.

 

Come on squeeze the last little bit out of it and get another 10 more degrees. I'm at roughly 160 out of the center vents. But yes I tend to agree with @Tractorman I think you won that battle. 

[Tractorman]

33 minutes ago, JAG1 said:

I took me two tries to get that mouse, was very skilled at taking the peanut butter and not setting off the trap

 

My mom lived in a cabin north of the Arctic Circle for years.  She used a single raisin for mouse bait.  She had it down - one raisin used over and over will take out many mice for several weeks.  The mouse has to tug fairly hard on the raisin and then..., well, you know.  Sometimes, because of all the commotion, you would have to search for the raisin so that you could reuse it.

 

- John

[01_Cummins_4x4]

4 hours ago, Mopar1973Man said:

 

Come on squeeze the last little bit out of it and get another 10 more degrees. I'm at roughly 160 out of the center vents. But yes I tend to agree with @Tractorman I think you won that battle. 

I think I won even more now. As I was driving it back down the mountain from my family's ranch, I had the infrared thermometer right against the dash vents, on full heat/ high fan speed, and I got 171* max temp.

[Mopar1973Man]

14 hours ago, 01_Cummins_4x4 said:

I had the infrared thermometer right against the dash vents, on full heat/ high fan speed, and I got 171* max temp.

 

Be careful. Don't let the hot air blow against the nose of the temp gun it will skew the reading make sure you shooting at 45-degree angle out of the air stream. The heated air can warm the plastics making the number skewed higher. Yes, I know this flaw because in the summer I can stuff the nose of the temp gun in the vent and see 15 to 20 vent temperature but a normal HVAC thermometer will show actual at 34 to 36 degrees.

[01_Cummins_4x4]

I tested it again with the temp gun at a 45* angle like you suggested, and I got to 160 temp.

 

Now here's another question for you all. 

 

Since selecting "Max AC" mode while in full heat, my blower motor spins much harder and faster, resulting in excellent heat output, like way hotter temps.

 

It's not beneficial to drive in the humid or middle of winter on recirc air obviously, so having to switch it from Max A/C to defrost or defrost/floor blend, is more cumbersome.   

 

I've never heard of it done yet, hence this question. Is there a way to modify the heater blower motor to blow as hard as it does on Max A/C, and to have it blow that same amount on the regular "outside air" heat modes?

 

 

Edited December 12, 2023 by 01_Cummins_4x4

[Mopar1973Man]

The only difference is the outside air is shut off by a vacuum motor. Wiring of the blower there is nothing special. It's the loading of the blower motor where the air comes from. There is no increase in voltage to the motor since on hi it gets a full 12V DC.

[Tractorman]

On 12/11/2023 at 9:49 PM, 01_Cummins_4x4 said:

Since selecting "Max AC" mode while in full heat, my blower motor spins much harder and faster, resulting in excellent heat output, like way hotter temps.

 

On 12/11/2023 at 9:49 PM, 01_Cummins_4x4 said:

I've never heard of it done yet, hence this question. Is there a way to modify the heater blower motor to blow as hard as it does on Max A/C, and to have it blow that same amount on the regular "outside air" heat modes?

 

A couple of things going on here that are not frequently talked about.  In the rear doors of the quad cab there air passageways in the lower rearward part of the doors.  Each door has an airflow entrance and an exit.  The entrance is exposed to the inside of the cab when all of the doors are closed.  The exit is exposed to the outside area beyond the door seal when all of the doors are closed.  You will have to open the rear door to view the exit.  I believe (but have not proven) that there is a membrane inside the rear door vent that acts as a check valve allowing air to only flow outward. 

 

So, anytime the outside air is selected, the air will flow from the outside cowling behind the engine hood through the blower fan into the cab and then finally through rear door exits.  This long flow path somewhat restricts the airflow.  Air flow will improve at faster vehicle speeds as a result of the difference of air pressure  - higher at the inlet (cowling behind hood) and lower at the outlet (rear doors of the cab).  The difference of pressure has a venturi effect.

 

When Recirc is selected, the re-circulation door near the inlet of the blower fan closes off outside air and opens a path directly from the inside of the cab to the blower fan inlet.  This short path offers much less restriction to airflow, consequently more air comes out of the vents.  Also, the air re-entering the blower fan will be much, much warmer than if outside air was selected, especially if outside temperature is well below freezing.  The part you mention about, "my blower motor spins much harder and faster"  is  probably not true.  It may SOUND like it is spinning faster, but what you are hearing is lots of blower fan noise and more air movement because the re-circulation door is open to the inside of the cab (where your ears are).

 

Something in general about non-positive displacement fans that move air - the least restricted air path will load the fan the heaviest (slower rpm's, more air flow) - the most restricted air path will load the fan the lightest (higher rpm's, less air flow).  This is contradictory to what most people believe.  Listen to a vacuum cleaner motor when the suction hose is blocked - air flow is virtually stopped, but the motor speeds up.

 

On very cold mornings (well below freezing) I use the Recirc mode to warm up the cab faster.  I switch to outside air when I start driving. 

 

- John

 

 

 

[Mopar1973Man]

For me and what I've done to my truck I'm now taking 15 miles to reach fully warmed temperature on the engine. I'm also not burning much fuel with low EGTs. So idle warm up isn't going to work. 

[Doubletrouble]

 I have tried the recirc while driving, it does kick out quite a bit more heat. I to will do this to get the cab warmed up on a cold day then switch back to outside air once cab is warm enough.  My truck don't seem to see the vent Temps near 160° like you guys. I've gotten to 135 I think (been a while since I checked it) bit I haven't wanted to pull the hvac box again to investigate. The heater core and a/c coil have both been replaced so no real need to do all that work again. It gets warm enough I guess. I do run a winter front for the colder months and a 190° t-stat.

 

 I got off track, what @Tractorman described is accurate. There are air fliw vents to allow the cabin pressure to remain neutral regardless of fan speed i believe they also help during summer months for a/c and when you have a window slightly open.

[Mopar1973Man]

 

I know this has the old school fan switch but the wiring is the same for later 24v truck. There is nothing different to the early and late blower motor wise. I think there is less restriction on the Max A/C setting more so than power difference at the motor. Recir air will always warm faster as long as your A/C compressor is not over whelping the HVAC like my truck likes to do most days. I tend to use the bi-level setting while driving but even that will possibly pull the temp down more with my A/C compressor going.