Question about Heating & Cooling

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I can help you with this but it is a good-sized job. You have other things you must do as well. First I need to know why you are replacing the evaporator is it leaking or plugged? The reason I ask is if it is plugged then you have contamination coming from the hose or the compressor which means you will have to replace the rubber hoses and or blow out the old hoses and see if anything comes out of it. And if your doing it because it is not cooling then you need to first pull the Orifice tube to see if it is plugged, because if the orifice tube is plugged it will cause the AC not to get cold, and goes directly to the Evaporator. To check it first unhook the nut on the line going to the dryer receiver the line will have a slightly larger tube on one side when you remove the nut pull the line apart and with a pair of needle nose pliers pull the plastic tab out of the enlarged tube. When you pull it out you will see a small screen notice it if has anything blocking it. Like rubber or metal, this is important because it will tell you what you need to replace depending on the contamination on the screen. Just to let you know it's against the law to dump the refrigerant out into the atmosphere it is to be vacuumed out by a shop so that it can be filtered and reused. Next using two wrenches to back up the one side of the line on the loosen the nut and unhook the line, any open lines tape them shut so they don't get air in the system, the moisture from the air will cause an acid when mixed with the refrigerant and will destroy metal and hoses. Now disconnect the clamp that holds the receiver/dryer on and empty the oil out of the dryer, see if it is clean, if not you will have to drain the oil out of the compressor as well as back flush all the lines. You can buy back flush for AC systems from most auto parts stores. Next disconnect the low-pressure side switch from the dryer. And remove it, I recommend replacing the switch as they leak with time
Now to remove the Evaporator if you are sure it needs replacing you will have to take the bolts out of the plastic housing and on some rigs it's inside the cab and others it's in the engine compartment, if it's outside in the engine compartment you will have to remove the twelve screws that hold the plastic part on, at this time disconnect the return line from the Evaporator, if the evaporator is on the inside then you must pull apart the plastic housing that the evaporator is in once you have the case half off be careful to not damage the gasket or the blend door motor or hose. Once you have it loose remove the rubber grommets that hold the pipes on to the firewall with a flat tipped screwdriver slightly oil the lines with the oil you drained out of the receiver dryer. Then work off the grommets, as you will need them again. Then install the new evaporator and install the new grommets, make sure you tape the ends so that when pushing the evaporator in place that you do not get any crude in the evaporator.
Next remove the compressor and dump out the oil in the compressor and measure it so you will know how much to put back in. use the spray can back flush to clean the compressor out. Then reinstall compressor next buy a set of o rings and a orifice tube and 10 to 12 ounces oil compressor oil or refrigerant oil, if you have R134A get Pag oil, you do not want to mix oils so get the one for R134A. Now pour about 6 ounces into the dryer and install the dryer into its holding clamp remove any old o-rings and use a q-tip to oil the rings replace the o-rings and bolt it back together. Put a tiny amount of oil on the orifice tube slide the tube into it's cavity making sure the flat spot is flush to the wall and be sure to install it with the flat side towards the condenser, Replace the o-ring by the tube and lightly oil it. Be sure to flush out the condenser before rebooking lines. When you pulled out the orifice tube if you found rubber in the screen then replace any rubber hoses that are used so it will not plug up again, when the compressor is running in max mode the pressure will go to as high as 325 PSI and the temperature will reach as high as 125 F. or more so do not chance using an old hose if you find rubber in the screen. Next add three ounces of oil into the compressor. And replace the o-rings to the compressor there are several types one bolt holds both lines on or two screw on types hoses. Replace the o-rings and lightly oil, the old o-rings will look flat and square cut but they are not they get that way over time the rings must fit in the grove and stick part way out to seal, just for your information you might think they gave you the wrong o-ring kit. Now remove the tape from the evaporator install o-rings and reconnect the lines install the low-pressure switch in the receiver dryer and reconnect the electrical lines. Now take it to a shop and have them vacuum it down and add the refrigerant, unless you have your own evacuation machine. There are two type systems add on after market and then there is factory you did not say which that is why I can’t be more specific about the evaporator as it is mounted different if it’s after market, and sometimes people have the dealer add them on when they buy them and even thought the dealer installs it it’s still considered after market. Do not add oil tothe evpaerator or the condensor and replace the Compressor belt at the same time. good luck hope this helps.

Posted on Jul 22, 2009


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