AC system low and high side pressures.....

[CanadianTRD]

Allright... I got everything done today. Took me most of the day, part of the slowness was the kids running around and a movie run late in the afternoon.

Anyway, everything went pretty smoothly. I replaced the compressor, the expansion valve, condenser and drier. I did not get any pics cause it was hot and I was dirty. I did not want to take the time to wash hands to take a picture.

When I had the refrigerant pulled out, there was 1.87 pounds in it. A wee bit overcharged. Weird thing is what was in there is fluorescent green. Now its clear like it is supposed to be. No big surprises and the hardest part was pulling the cooling unit from under the dash, and even that was not difficult. I bought 2 12 ounce cans of Dupont Suva 134a and both cans went in for a total of 24 ounces. The high side of the recommended charge is 1.5 pounds and both cans puts me right there. I should have stopped before dumping the entire second can in, but something I did not expect was happening. I could not get the bubbles in the sight glass to go way. So after dumping all 24 ounces in, I read in the FSM that on very hot days, even a correct charge can show bubbles in the sight glass. It was 92 here today and I got the duct temp down to 58. Should be colder but it was hot and humid today. With idle at around 1500, low side is at 35psi and the high side goes between 180 and 250.

Aside from the initial cost of the equipment necessary to perform this work, I would encourage anyone else to work on their own AC.

Nice work! And even nicer pressure readings, those are better than factory lol
BUILT NOT BOUGHT. It's always more satisfying in life to DIY than otherwise, then you now know a new skill, and you can teach others too! Not to mention saving a boat load of cash that can be spent on proper toys :thumb3:

 

[opie74]

Did you vacuum down the system? and for how long.

Yep, ran it for 5 minutes before buttoning everything up then shut it off to see if the vacuum held. Then ran it for 30 minutes while I put everything back together.

BTW. The florescent green was a dye that was installed sometime before you got the 4runner and some time after it was sold from the dealer. The use of a UV light would make finding leaks easy with the dye in the system.

Didn't think of that, makes sense.

 

[opie74]

Nice work! And even nicer pressure readings, those are better than factory lol
BUILT NOT BOUGHT. It's always more satisfying in life to DIY than otherwise, then you now know a new skill, and you can teach others too! Not to mention saving a boat load of cash that can be spent on proper toys :thumb3:

Thanks.

Went out this morning to check outlet air temp and its down to 45. Ambient is 71.

 

[bootown]

Aside from the initial cost of the equipment necessary to perform this work, I would encourage anyone else to work on their own AC.

I need to replace the expansion valve and have one question. How do you disconnect the clamp on the liquid tube in the engine bay?

 

[Singtoe]

I need to replace the expansion valve and have one question. How do you disconnect the clamp on the liquid tube in the engine bay?

I use a pick . insert into to rectangular opening, disengaging the metal tangs for the clamp. Then open.


Don't forget to vacate the Freon before hand or you might get a big surprise when you open the clamp.

 

[bootown]

I use a pick . insert into to rectangular opening, disengaging the metal tangs for the clamp. Then open.


Don't forget to vacate the Freon before hand or you might get a big surprise when you open the clamp.

Awesome, thank you. My a/c doesn't blow cold and the shop that I spoke with says I don't should not need to discharge the system since there would be little, if any, refrigerant left. Hopefully their right.

 

[opie74]

I use a pick . insert into to rectangular opening, disengaging the metal tangs for the clamp. Then open.

Yep, I used 2 pins stuck into the smaller holes. Whats in there is a metal tab and you need to push it away from the outside of the clamp. Then it will open right up.

 

[opie74]

Well, something is not right. Gauges show pressures are good...

The suction line into the evaporator is cool, not cold. Liquid line is hot, condenser is hot and the air coming out of the ducts I can not get below 60 degrees. Ambient right now is 89. The blend door appears to be closing completely.... I pulled the thermistor and put my fingers on the evaporator and its not cold at all. But there is water dripping from the drain. Compressor never cycles but I can assume thats because the temperature of the evaporator never gets cold enough to cause the compressor to cycle. Bubbles come and go in the sight glass, but with the * disclaimer in the FSM, not sure what they consider "unusually warm." 2 12 ounces cans of 134a should put me right at the upper limit of the charge weight, so it cannot be a lack of refrigerant.

Im stumped.

 

[Singtoe]

I would pinch the heater line with a c-clamp to stop the flow of antifreeze through it. Then check it out. If it the same, then it sounds like tour expansion valve is defective.

 

[opie74]

Well, I had the gauges hooked to it with the dash torn apart to make sure the blend door was closing fully.. Low side pressure is fine with increased throttle, but as soon as I let the throttle drop to idle, the low side shoots up to 60 and the clutch starts slipping. The limited reading Ive been able to gather, including the FSM points to the reed valves in the compressor. High side stays within spec.

But it could be the expansion valve.

 

[austinringding]

I found this thread and was reading it as i'm having very similar issues with my A/C on '96 4runner.

Would you be so kind to let me know how it turned out?

You never came back and updated the thread.

Thanks!

 

[opie74]

Austin, I received your PM and will address your questions here so they are public.

I ended up receiving a defective compressor the first go round. After exchanging the compressor, everything is working smoothly. I can get duct temps down to 40-45 on a 90 degree, full sun day.

I believe my initial issue was the compressor was failing and clogging the lines with stuff.

I will answer any questions as best I can.

 

[austinringding]

Thank you for returning opie.

I am still having issues with my A/C on a hot day. Cool days not so much, but it is still intermittent during the hottest days here in Central Texas.

The issue started last summer when it begin cooling intermittently.

I had a mobile A/C specialist come by to check out the truck at my house.
He put his gauges on it and determined that the Freon was low and added some. How much i'm not sure. He then put the gauges back on it and noticed that the pressures were doing weird things and told me that it was something other than just the Freon. I had told him that the engine was having overheating issues as well, and he said that may have something to do with it and to fix those issues first and then get back to him.

I replaced the thermostat, radiator cap, fixed the leak in my radiator and topped off the coolant. I have not had any more overheating episodes since doing all of that.

Fast forward to this summer and the A/C is still intermittent.

So I had another guy from work lend me his Snap On gauges and I hooked them up on a pretty hot day. A/C was blowing cold when i started.

Low side initially showed about 35 and high side was about 300, but started rising up to about 350. Over about 5 minutes the low side started dropping and eventually got down below zero to the inHg Vac part of the gauge, and got to 20 on that scale (green). High side dropped down to 200.

I still have the gauges with me, so i can do further testing as needed and could even do a video if it would help y'all help me.

The only other detail i'd like to add is that I just replaced the fan clutch with a brand new OEM Aisin fan clutch and redid all of the serpentine belts.

I am now leaning towards replacing the expansion valve behind the glove box as it's the least expensive route to take.

If it does end up being the compressor, i would like to have it rebuilt as opposed to buying a new one.

Also, where do people have the Freon evacuated? Does JiffyLube do it?

 

[opie74]

Part of the issue (in general) is air flow over the condenser. If there isn't enough airflow through the condenser, the heat can not be carried away from the refrigerant. This is why the air is colder while moving rather than sitting still. I still experience this. Itll blow 40 on the highway, but maybe 60 in town.

Im not an AC expert and hopefully someone that knows what they are talking about chimes in....It does sound like your expansion valve based on the numbers. Keeping in mind the current temp and humidity will play a role on the numbers you see. IIRC, 35 on the low side at idle is OK, if its 70 degrees out. As the temp increases so will the pressures on both sides. I found that placing an electric fan right in front of mine, on high, helped me get more accurate readings. Also, in order to do it correctly, pressure readings should be taken with the engine at 2000 RPM, but idle is usually sufficient.

As for replacing the expansion valve.... It may be the cheapest part, but you have to draw all the refrigerant out of the system anytime you open it up. Its also recommended you replace the drier anytime you open the system up... Keep that in mind as it will add to the cost. Unfortunately the associated costs of throwing parts at the AC system are a bit different than say plugs and wires.

Does the compressor ever kick itself off, or "cycle?" The temp probe may not be telling the compressor to kick off and the expansion valve and evaporator are freezing up.

Im not sure if JL will do it. Wherever you take it, make sure you record how much they take out so you don't have to re-buy the refrigerant they take out.

I found a brand new Denso compressor on Ebay for IIRC $150.

 

[austinringding]

Worried that the fan clutch wasn't working properly, and not pushing the correct amount of air over the condenser is why i replaced the fan clutch. A buddy of mine had just had the same issue and replacing the clutch fixed his issue. No such luck for me.

I am definitely going to take further readings while i have the gauges. Problem is, it's always about 100 Fahrenheit around here for the next few months. Uggh.

I am aware that I will have to evacuate the line, and have been told that I need to replace the drier as well. I'm having trouble finding anyone to evacuate the line only. They want to evac then refill. Won't work for me as I'm going to have to take it home to work on it.

The compressor does cycle and quite a bit with the A/C on during a hot day. Almost once every 30 seconds or so. What / where is the temp probe and is it replaceable?

Also, what causes the expansion valve to be the culprit? If it's clogged up from the compressor spitting out junk into the lines, then replacing the valve wouldn't resolve my issue would it? How can i determine if it's my compressor or not?

 

[opie74]

Thats one of the problems with a belt driven fan... You get some air flow while sitting, but not as much as needed. (sometimes) Thats also why vehicles with electric fans kick the fans on when the AC is on, so there is airflow over the condenser.

Current temp isn't an issue, so long as you compensate for it. There should be readings on the gauges to correspond to the current ambient temps.

EVAC... I am fortunate to have the ability to have it done where I work. Find a small garage/shop and give them a call. The chains and larger places care more about liability and bottom dollar than the local, on the corner, mechanic.

The temp probe is on the evaporator. You will see it when you pull the evaporator to change the expansion valve. There is also a pressure switch that will kick the compressor off if the pressures get to high. Watch the gauges and see at what pressures it kicks off. With the low side going into vacuum, that tells me something is plugged, but the compressor is working.

Since you are taking it apart, I would pull the lines, condenser and evaporator and flush them out. The hard lines will pull through the firewall once you disconnect the evaporator and the rubber lines are relatively easy to get out. Pull the condenser as well to flush. You can buy the AC flush at your local auto parts store, lest I was able to. One thing to note, though. You will have to add oil to the individual parts you flush to replenish whats cleaned out. Ideally you take the total volume of oil thats supposed to be in the system and split it evenly between all the components.

On determining the effectiveness of the compressor.... I am not sure. You are going into a vacuum on the low side so that indicates that will actually pull a vacuum..... Which to my understanding is what the low side does anyway, it only shows pressure because the pressure in the system overrides the vacuum. Someone more experienced than I can answer that question perhaps... If it were me, I would replace it while I have the system taken apart. But Im a "do it all at the same time" kind of person, which is a little OCD. And Im fine with it.

 

[vipergrhd]

Not an expert

I just read all your post and for the most part most of you have an understanding how a basic a/c system works,but there are some info in here that completely blew my mind LOL. I will just share what i know and learned over the years and i will leave it up to you guys if you follow it or not.

Lets start with gauge readings,this is on an average vehicle were everything is working the way they should,low side reading should be between 20-40 psi high side reading (ideal) 100 psi plus ambient temp.this could vary depending on what type of cooling fan is used,250 on high side is still normal anything past 300 psi look for a blocked condenser or fan is not working as they should.Humidity is a big factor to any a/c system don't expect you system to blow 40* on a very humid day i would suggest to add a water sprayer in your condenser if you live in humid places believe me it works,try spraying water in the condenser when your system is running and see how much temp.it drops.

When your replacing the entire system or even just a compressor avoid over oiling the system here is an ideal capacity of oil for most vehicle out there,most a/c system will hold 6-8 oz.of oil do not add all of the oil in the compressor here is the break down,compressor 2-3 oz. condenser .5-1.5 oz evaporator 1-2 oz reciever /drier or accumulator 1-2 oz. the accumulator is mounted on the low side and receiver /drier is on the high side accumulator usually holds more oil than a drier.before you start charging or vacuuming the system turn the compressor clutch by hand about a dozen times to avoid choking your compressor when it initially engages when you vacuum the system rule of thumb is the longer the better.an expansion valve is just a regulator that control the flow of refrigerant to your evaporator your gauge will tell you if it's working or not.the system has a few switches or thermistors depending on the car maker high pres. switch and low pres.switch are just that switches to turn things on and off,some system uses low pres. switch to cycle the compressor it will usually turn off below 20 psi and the high pres. switch is just the opposite which turns the clutch off when it reaches 400-450 psi and avoid bleeding the system out of the blow off valve.

Most a/c system from the factory is a bit overcharge (very true) so don't be afraid if you think you did overcharge your system you can always evacuate or bleed out.most new system will blow 40* out of the vents on an 80* day and a good working a/c will have a 40-45* drop from ambient,so don't expect your a/c will still push 40* when it's 100* plus ambient temp.I hope this helps you guys and feel free to comment if i miss something or if you think i'm blowing smoke up your :tape: