Love my truck, haaaaate the A/C

Yahooligan · 10-20-2011, 12:31 AM

Apparently I'm not the only one that has complaints about how well the A/C works (or doesn't), I'm curious to know if anyone has found a "fix" that doesn't involve bypassing the heater core.

Basically, whenever it's "hot" out (Say 85-90 or higher) the A/C just doesn't do a very good job of cooling the cab down. Had the A/C checked and the proper amount of refrigerant installed, no leaks or anything. The receiver/dryer and lines are cool (laser/IR temp sensor says low 40s) so I know the system itself is cool, but man...I hate driving my truck in the summer.

Now that the weather is starting to cool down (60s and 70s) I finally enjoy driving my truck again. If we take a long drive then eventually the cab cools down to a comfortable level, but around town it just doesn't cool down fast enough and then I'm where I'm going.

Anyone else suffering with the same issue? Anyone find a fix? I know a lot of it has to do with the sheer amount of airspace inside the MegaCab.

Hop in the wife's Challenger and the cabin is cool within a couple of minutes.

RCrawler · 10-20-2011, 12:56 AM

Might be a Mega Cab thing, might be a 3rd gen thing, but my '08 never did work all that great. It would cool like it should (down to 40 deg F from the vent), it just didn't have the fan air flow. And the way that the vents were designed, I couldn't get any direct flow towards the driver

That's one thing that sold me on the newer trucks. I drove my sister's 2011 1/2 ton and the A/C worked awesome and the vents could be aimed to hit me directly.

Flopster843 · 10-20-2011, 10:47 AM

The megacab trucks have some air flow screens inside the HVAC system in the dash to help direct airflow to the rear vent. If you cut out those screens you will get much more flow to the front vents and the rear will still work. There are instructions on here somewhere for how to do it, just search for it and you'll eventually find it. But this only affects flow, and won't do anything for vent temperature.

Hands down, the best modification you can do for the factory A/C is to bypass the heater core. I got a 10* drop across the board when I bypassed mine. Plus it's much easier than taking the dash apart to get to the screens.

pjesson · 10-20-2011, 11:01 AM

Quote:

Originally Posted by Flopster843

The megacab trucks have some air flow screens inside the HVAC system in the dash to help direct airflow to the rear vent. If you cut out those screens you will get much more flow to the front vents and the rear will still work. There are instructions on here somewhere for how to do it, just search for it and you'll eventually find it. But this only affects flow, and won't do anything for vent temperature.

Hands down, the best modification you can do for the factory A/C is to bypass the heater core. I got a 10* drop across the board when I bypassed mine. Plus it's much easier than taking the dash apart to get to the screens.

I have thought about your heater core bypass several times. Of course it isn't important in October and I won't really care again until about April/May of next year but the subject is on the table.

Have you got the electric bypass working like you describe in your detailed instructions? I was also considering the following alternative.

If I installed a T joint in both of the hoses going to/from the heater core then connected these with a hose that had a shutoff in it I could effectively just open the tap to provide "bypass" behavior and shut it to provide stock "heating" behavior. Sure, the bypass wouldn't be 100% bypassed because some flow would still go through the core but assuming the resistance is less through my straight pipe the majority of the flow would go through that rather than the core. In "heat" mode it would be as good as stock. In "cool" mode it would be less good than your suggestion, but potentially pretty close. And the switchover could be done in a minute with the hood open.

I used to own an MG Midget that had a tap under the hood that turned on the heat. Similar idea.

What do you think?

BTW. For those that don't know, John has wonderful detailed instructions on the page in his signature for several mods he has done. I've even added that page to my favorites.

Yahooligan · 10-20-2011, 01:47 PM

I had thought about doing a bypass with valves as well. If you did 2 valves, one past the inlet "T", then you could completely bypass the heater core quite easily. Plenty of time between now and next summer to come up with a plan.

pjesson · 10-20-2011, 03:22 PM

Yeah, I considered that too.
Doing it with 2 valves would allow you to accidentally shut them both off and cook the turbo.

(I could probably trust myself to do it right but. Just last week my wife phoned me at work to ask how to turn off the water to the kitchen faucet which was leaking. I told her....came home 5 hours later to find the dishwasher dry cleaning the dishes and the faucet leaking all over the counter. If she cooked my turbo I might end up in jail.)

I wonder if you could find a manual T valve that went one way or the other but not off. That way it makes it beer-proof. I haven't seen such a thing but maybe a specialty plumbing place? It has to tolerate high temps and fit inside 3/8" ID hose right?

Flopster843 · 10-20-2011, 05:51 PM

You mean this thing?

The valve is installed and works great, but I haven't had a chance to finish the control knob for the cab, so I haven't updated the article yet. And don't mind the date stamp, I can't ever remember to change it before I take the pictures.

pjesson · 10-20-2011, 06:20 PM

Flopster, you do nice work. That looks like a very nice installation. And you write great, detailed, informative articles too. I'm really looking forward to the writeup on this one.

What does the control that you are going to put in the cab do? I mean, I know what it accomplishes, but effectively what is it? A toggle switch? A reostat? It would be really slick if you could intercept the signal from the heat knob and direct the water through the heater core if the heat was turned up above some fairly low level. Anyone know if the heater knob is just a reostat? Maybe tapping that could provide a signal that could be directed to a relay which would un-bypass the valve.

Of course you have been scheming on this for a while already and I'm just getting started so I'm probably not giving you any new ideas.

Flopster843 · 10-20-2011, 07:08 PM

The valve is a variable position valve controlled by a rheostat. But it's not a normal rheostat. It has 5 wires in it and I couldn't figure out how to change it over to a simple on/off switch, so I have to have the rheostat mounted in the cab somewhere. I tried to tap into the OEM electronics to control the valve but it was a no-go. The HVAC controls utilize the CAN BUS communication system so I couldn't pull raw voltage out of it to make it run the valve.

I can't stand hack job installations, so simply drilling a hole in the dash and putting the switch there just doesn't suit me. Plus I like to over engineer and over complicate even the simplest of things. So I acquired a 4X4 selector switch out of another truck and modified it to house the rheostat inside. The only problem now is I can't figure out how to get the face looking good. I checked into getting it screen printed to say "Heater core bypass" but it was going to be $100 to do it.

So I'm trying to locate other options that would be more affordable and look like an OEM installation. I'm thinking about just having a red/blue bar painted around the knob like the center knob on the HVAC controls.

Here's a couple of pictures of the control knob and a failed attempt at home-made stencils.