Air Conditioner Performance Upgrade by Flopster843 30 Jul 2010 To put it simple, the OEM air conditioner system installed in Dodge trucks just flat out sucks. With ambient temperatures in the low 90s, the coldest I was ever able to get my vent temp was 51 degrees. 51 degrees might be an acceptable temperature for a house HVAC (Heating, Ventilation, and Air Conditioning) system where the inside temperature never fluctuates more than 4 or 5 degrees, but it definitely falls short in the cab of a truck where the temperature can elevate 50 degrees over ambient from sitting in the sun all day. I have decided to create a little project aimed at creating a more acceptable vent output temperature for my truck. A vent temp somewhere in the upper 30s to low 40s is sufficient and is my goal with these modifications. Keep in mind that you never want your evaporator (inside radiator thing in your HVAC box) to drop below 32 degrees. If it hits 32 degrees or lower, all the condensation that it naturally collects will freeze, which will cause all of your air flow to stop and completely disable your entire climate control system until it thaws. This is an ongoing project showing all the different phases of modification and a chart showing vent temps after each mod. This should allow you to see which modifications provided the best bang for the buck and help you decide if you wish to do any or all of these to your truck. Table of Contents Progress Chart... Pg 2 Phase 1: Ensure Proper Air Conditioner Charge... Pg 3 Phase2: Heater Core Bypass... Pg 5 Option 1: Manual Bypass with heater hose... Pg 6 Option 2: Automatic Bypass with Bypass Valve... Pg 10
Progress Chart Stock Phase 1 Phase 2 High Idle, Fan speed 3 54*F 54*F 44*F High Idle, Fan speed 4 59*F 59*F 47*F 60 MPH, Fan speed 3 51*F 51*F 41*F 60 MPH, Fan speed 4 54*F 54*F 43*F Notes: Measurements were taken with an ambient air temperature of 94*F. High Idle measurements were taken with the truck at operating temperature, parked in front of my house, with the high idle feature engaged to raise engine RPMs to 1100. 60 MPH measurements were taken with the truck at operating temperature, on interstate I-26, cruise control set, and no load in/behind the truck. 2
Phase 1: Ensure Proper A/C Charge Start by ensuring your factory air conditioner is working properly. This is accomplished by simply having the Freon charge checked in the system. It s not uncommon for some vehicles to be under-charged or over-charged from the factory. You must utilize a refrigerant reclaiming/recharging machine or a good set of gauges. The cheap cans you get from the auto parts store with a built in color gauge do not work. You should never utilize those cans to check the charge of your air conditioner; you can easily over/under charge the system and cause severe (and expensive) damage. I suggest taking your vehicle to a reputable shop to have this operation performed. My truck was properly charged from the factory, so this netted zero improvement. The shop I went to has one of those all-in-one machines. You simply attach it to the truck, type in what you need, and hit go. It ll evacuate and reclaim all of the Freon from the system, draw the proper vacuum, and then recharge appropriately. 3
The other option is to recharge utilizing gauges. The main problem with this is that gauges can t evacuate the system and reclaim the Freon. Remember, it is illegal to discharge Freon into the air, so you can t just hold the valve open like you would with a tire. Plus if you do this, you do not have any means of pulling the proper vacuum on the system. Use the chart below to determine the proper pressures required and vent temperatures. Proper compressor oil level 7 ounces (210 ml) Proper Freon charge 1.0 pound, 10 ounces (0.737 kg) Air Conditioner Chart (applicable to 2008 Dodge Ram 2500 with Cummins engine) Ambient Air Temperature A/C Temp at Center Panel Outlet Compressor Inlet Pressure at Service Port (Low Side) Compressor Discharge Pressure at Service Port (High Side) 21*C 27*C 32*C 38*C 43*C 70*F 80*F 90*F 100*F 110*F 7*C 7*C 13*C 13*C 18*C 45*F 45*F 55*F 55*F 64*F 138-207 kpa 172-241 kpa 207-276 kpa 241-310 kpa 276-345 kpa 20-30 PSI 25-35 PSI 30-40 PSI 35-45 PSI 40-50 PSI 1034-1724 kpa 1379-2068 kpa 1727-2413 kpa 1999-2689 kpa 2413-2965 kpa 150-250 PSI 200-300 PSI 250-350 PSI 290-390 PSI 350-430 PSI 4
Phase 2: Heater Core Bypass Since phase 1 of this project netted me zero change, I decided to take it to the next level, a heater core bypass valve. By default, the HVAC system on most vehicles sends the air through the heater core and the A/C evaporator on the same pass. Dodge utilizes the blend door to mix the hot air from the heater core with the cold air from the evaporator to achieve the desired temperature. On many vehicles, including the Ford Superduty, the factory installs a shutoff valve to isolate the heater core when the air conditioner is on max. This eliminates the hot water flowing through the heater core, which eliminates the heat inside the HVAC box, which helps to lower A/C temperatures. Dodge somehow forgot to install such a valve on these trucks, probably due to production costs. NOTE: On the 6.7L Cummins engine you must BYPASS the heater core. You cannot block the flow with a shut-off valve. The reason for this is that the turbo is cooled via the return line from the heater core. If you stop all flow, you will cook the turbo. See the picture below. Heater Core Return Turbo Cooling Line 5
Phase 2, Option 1: Manual bypass with no valve This is the cheapest and simplest way to bypass the heater core. All you re going to do is run a line from the head to the metal stand pipe that the heater core return connects to. The only downside to this is you will have no heat at all. To get the heat working again, you ll have to re-attach the factory hoses. Step 1: Gather the required materials that you ll need to bypass the heater core. You will need 22 inches of 5/8 heater hose. I purchased a 6 foot roll at the local NAPA for about $10. I only lost about 2 cups of coolant while doing this, so you shouldn t need any make-up coolant. 6
Step 2: Disconnect and remove the factory heater core hoses. I highly suggest you do this in the morning after the truck as sat all night. After you drive it, it will remain too hot to work on for hours. The hoses are attached to the truck with spring-style clamps over the hose barb connectors. Simply squeeze the clamps with a pair of pliers, vise grips, or your fingers if you re really buff, and slide them back. Then slide the hoses off of their connection points. The two clamps holding both hoses to the heater core are a beast to get to because the part you have to squeeze faces directly into the head and it s nearly impossible to get to them with pliers. I managed to rotate the bottom one around to the 7 o clock position and grabbed it with a pair of needle nose vice grips. Then repeat for the top once the bottom hose is off. 7
Step 3: Cut your first piece of hose to 6 inches in length. Install this piece of hose on the heater core connectors with the factory hose clamps, making a loop between both outlets. This is simply to cap off the heater core to keep crud from collecting in it while it s not being used. Step 4: Cut the second piece of hose to 16 inches in length. Install this piece on the hose connection in the head, run it around the back side of the EGR cooler, (if it s still on the truck) and connect it to the metal stand pipe where the heater core return used to connect to. Utilize the factory hose clamps to keep it in place. 8
Step 5: Start the truck and check for any leaks. Add some make-up coolant if you need to, but I doubt you will. This modification netted me approximately a 10 degree drop in vent temperature, and it only cost $10. I think $1 per degree of temperature drop is sufficient. After all, who wouldn t want to add horsepower to your truck for $1 each? Afterthought: The bypass heater hose does rub slightly on the upper portion of the engine cowl. I would recommend checking it periodically to ensure it s not chaffing, which would lead to possible failure. If you re going to leave it on long term, it might be a good idea to insulate the hose with something to prevent any chaffing or try to isolate it from the cowl. I don t plan to leave it on forever since I m going to automate it with a valve. See Phase 2, Option 2 for details. I did leave the hose installed for a full summer and didn t notice any chafing marks on it when I removed it. 9
Phase 2, Option 2: Bypass utilizing an electric bypass valve I am working on trying to install a bypass valve so I don t have to switch the hoses in my truck. The problem with this is most valves are vacuum operated and these trucks don t have any vacuum source. I have located an electronic bypass valve that is sold by Old Air Products, but I want to devise a way to wire it in for a factory-installed look and to make it completely automatic with the factory HVAC controls. If you decide to attempt this mod, or have any possible ideas, please let me know. www.oldairproducts.com/catalog/advanced_search_result.php?keywords=50-1555&oscsid=f97ff939d110881dc12ee5a75d17bdc5&x=33&y=11 10