So I have been asked to do a write up on how to replace the expansion valve on a 98 es, however I did not take any pictures. I'm writing this from memory so I am sorry if I miss a step or two. I'll do my best.
What you will need.
1. A vacuum pump (refrigerant system evacuation pump) You can rent one just make sure they give you the adapter that fits the low pressure recharge valve in your car and it has a gauge. If you can not find one for rent, you can have a local garage evacuate the system for you and check it for leaks with a leak down test.
2. A good 1/4" socket driver set with a 6" wire type flex extension. I have the Geardriver set from Gearwrench and I love it.
3. About 2 and 1/3 12oz cans of R134A one of which should include UV dye. DO NOT USE THE STOP LEAK TYPE! Unless you like to replace your expansion valve often.
4. Always replace the filter dryer whenever opening the system so get one of those too. It is located just behind the bumper on the co-pilot side.
5. Obviously you will need an expansion valve, a genuine Toyota one is preferred as you will only want to do this once in your lifetime.
6. A small bottle of PAG 46 compressor oil. Always cote o rings with pag oil and make sure your hands are clean. Also I use a small piece of tubing pushed over the o ring to keep dirt out while positioning the parts of the system.
7. An A/C recharging kit with a gauge that also displays ambient temperature range.
8. An A/C valve core tool and a new Schrader valve core for the low side valve.
9. A can of Toyota evaporator core cleaner/refresher, and just two beers.
Let's begin, this will take the average DIY kind of guy about 4 hours so open your first beer now, I am a seasoned mechanic and it took me 2.5 hours. The Mitchell manual suggests it should take 2.8 hours for the job. So get a friend and have a beer or two but no more than two.
Start by evacuating the system. It is illegal to release the refrigerant into the air but if you do you should have plenty of ventilation and NO OPEN FLAME, R134A is not flammable but when it burns the fumes will kill you! Now onto changing the filter dryer, it is behind the bumper on the passenger side and requires a 10mm socket or gearwrench. You should be able to reach under the bumper to get at it. There are two fittings on the top each mounted with a 6mm bolt having a 10mm head. Remove these first and then loosen the clamp assembly requiring another 6mm bolt on the right side of the dryer when looking at it from the front of the car. Once removed, replace the o rings on the fittings with the provided o rings in the box that the filter dryer came in and be sure to cote them in PAG oil. pour about an ounce of PAG oil into the new dryer and install. Just snug the bolts down DO NOT OVER TIGHTEN just snug is fine, its not going anywhere. Be sure to clean the little window on top, you will need it later. That part is done, try not to injure your arm while patting yourself on the back. An arm injury here will make the job take longer.
Now the real fun begins! Open the passenger door and take a knee. Remove the panel under the glove box, it is held in by a few clips. Now get into the co-pilot's seat and start emptying your glove box. If you can not figure out how to remove the glove box, you should go no further. It just takes a keen eye to see the bolts and screws that hold the glove box panel on (hint) there is a hidden one down to the right under the front edge of the kick panel cover. Once done, you will see what you are up against.
Next you will need to remove but not unplug the three modules on the right, the body control module, the ECM and the audio amp. Some wire harness clips will be broken upon un clipping them if you are not careful. I was not careful, that is what zip ties are for. Now get out and take a knee. there are lots of screws, a couple of nuts, and lots of bending to get at them but you only need to remove the blower plenum assembly to get to where you need to be. There are a few fasteners that are hard to see, but if you got this far you'll figure it out. There are two nuts at the top that are hard to see and some of the ducting pulls off while the one behind the pull off one on the left is held on by a hard to see screw. This is what the wire type flex extension is for, enjoy.
This is the part where you scratch your head and wonder how to get the blower plenum out. Don't worry, you just have to push the dangling modules to the side and turn it just right. There is a temp sensor here remove it carefully and do not forget about it. With that out of the way, you will see a cover to the left and the lines coming through the firewall covered in insulating foam. Carefully pull the foam back from the firewall to reveal another 6mm bolt, do not rip the foam unless you like the way mold and mildew smell in your carpet. Leave it alone for now and get the cover loose first, then remove the bolt and pull back on the lines to release the fitting. Now remove the cover and discover the evaporator core. Gently pull the evaporator core out with a wiggle and pull operation. I'm sure at some point you looked at the expansion valve and you should recognize it mounted to the evaporator core.
The evaporator core gets soaked in condensation all the time so it gets wet and wet makes bolts rust. Use some PB blaster or some sort of snake oil on the bolts and open your second beer. Take a few sips while the stuff works. Ok now carefully loosen the bolts, when they start to move you should work them back and forth a few times making little progress at a time. This should do the trick and hopefully you have not snapped them off. Now carefully pry the valve off being sure not to bend the lines or break them off of the core. If that was a success this would be a good time to clean the core and remove the leaves and crud from the hole that the core came out of. Be sure not to bend the fins! Use your core cleaner and follow the directions on the label. Confused? just spray, let sit, wipe and repeat.
Now lube up those o rings and slide them onto the lines. There are two large holes, one medium hole and one small hole in the valve making it idiot proof. You should be able to push the lines into the valve with a little force but it is easy to ruin the o rings as they will catch on the beveled edge of the valve or fold into the valve so unless you have an assortment of A/C o rings at your disposal you should be careful. Even I will trash one once in a while. Again DO NOT OVER TIGHTEN THE BOLTS! Now that you have got the valve installed, you can put it all back together. Remember the temp sensor and make sure it goes back where it came from or your A/C will drive you crazy!
All done? Here is the home stretch! At this point I can see nothing wrong with having a third beer. Go on you've earned it. Change the valve core and start to vacuum the system down. If you could not rent a pump, this would be a good time to designate a driver or wait till morning to go to a shop to vacuum down the system for you. If you do have a pump, vacuum the system down to 30 inches Hg (mercury) and let it stand for about 30 min. If the gauge did not move continue. If it did, don't cry, that is what UV dye is for. If it lost some vacuum, be quick and swap the pump out for the refill gauge with a bottle of 134 ready. If it lost all vacuum, you are screwed, get ready to tare it apart again, because you pinched an o ring in the expansion valve.
Start the car and set the A/C to maximum and on outside air. It will not work at this point but you know that. Start with the can that has the UV dye first. Start filling! About 2/3 of the can should turn the compressor on. (hint) Reach over and push the throttle assembly bringing the RPM to around 2,000, this will make the pressure on the low side drop quite a bit allowing you to get the whole can in. When empty or when the pressure drops to 5 psi or so, remove the empty can and grab the next one. Repeat the throttle trick again to empty the second can, this time you should end up with about 20 psi. Grab the third. Allow the engine to idle and load in the last can and watch your pressure, adjust the gauge dial to the ambient temperature and get the pressure to the low side of that range. Close the valve for a moment and go look at the window on the top of the filter dryer. you should see some small bubbles going by. Go back to the gauge set and open the valve a little to increase the pressure by a pound or two. look into the window, if you still see bubbles, repeat. Just when the bubbles go away you have it perfect! Remove the gauge and replace the cap, YOU'R DONE! Be careful not to over fill, if the bubbles go away, you add more and they come back you have over filled the system and need to let some out. The perfect zone is a matter of just 4 psi so take your time.
Once you have done this you will be able to shiver in your car while it is 100+ outside, no joke!
Have a leak? Get a $10 florescent black light from Spencer's and look for dye at each connection. When you find it, get some o rings and fix it then re-charge, just remember "any time you open the system you need to replace the filter dryer! There is no need to add more UV dye, the stuff you already put in will be there forever!
I hope this helps and saves you all some money! The job is really not that hard, it is just tedious and requires some time and attention. My total cost was just over $40 because I have the required equipment. A shop will generally charge about $50 to evacuate and leak test, so it's not so bad and in total will be cheaper than renting the equipment. If they try to charge you over a hundred, go to the next shop. Better yet just call around. I hate driving around in the summer with no A/C if I don't have too.
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All diagnostic wisdom is earned only from experience and study of other peoples wisdom. That is why I love CL. I get to learn and teach.