Spray water on the condenser for a minute and watch the gauges. You may not have enough air flow over the condenser. If so the water will drop both the high and low side pressure considerably. Getting adequate air flow will likely also indicate that the system charge is low.
And while you have a proper gauge set and seem to be getting along OK I would recommend that you locate the low pressure switch and disconnect it and jumper the harness with a short wire with a large piece of tape on it. I use a 1 foot piece of pink tape. If anything begins to look bad on the gauges or you hear or see anything troubling yank the jumper out and the compressor will cycle off. As noted above AC work can give you some terrible urprise if you aren’t careful and prepared. I have seen the high side climbing past 375 in a matter of seconds.
And is that pressure chart specific to your vehicle?
According to the pressure/temperature chart shown the pressure is within normal ranges. But then is that the pressure chart for the Highlander with two evaporators? Expansion valves vary in operation and they do operate to maximize cooling with the available pressure. And while I have worked on quite a few systems with expansion valves without controlling all inputs and seeing the manufacturers pressure/temperature chart I can only offer general suggestions.
But shooting from the hip I agree, @old_mopar_guy, the low side seems too high and on my best recollection of an R134 system with an expansion valve the high side is too low. But I wish the OP would confirm that chart applies to his car and what the gauge shows when the condenser is sprayed.
Just some food for thought, but the low side gauge shows about 55 PSI. That’s too high. The low side pressure is equivalent (roughly) to the evaporator temperature. The 60 to 70ish temperatures are way too high and the 55 PSI is likely the reason why.
Again (and this is just my method only) I charge by system pressures; not by the amount of refrigerant that is recommended.
When the system is working correctly you should see the accumulator/dryer line sweating and there should be condensation drips underneath the car from the evaporator housing.
That’s my method on cycling clutch orifice tube systems ok4450, and it often works on various expansion valve systems but the OPs late model Toyota is not familiar to me and the temp/pressure chart throws me a curve. Back in the good ole days R12 systems could be charged to 35psi on the low side and if the high side was below 275 and the low side hose from the evaporator was sweating and cold to the touch the system was working as expected but what refrigerant is in this vehicle? And if the condenser fan is not working properly what does the expansion valve do? The system may be overcharged and the expansion valve is opening to limit high side pressure and that would cause poor performance and high pressure on the low side.
As it has always been in automobile repair the manufacturer’s instructions don’t give detailed explanations of how the system operates. We must watch and measure and figure it out.
Good morning all,
My apologies on the delayed response. We are in the processing of selling our home and it’s keeping me busy. My next step is to spray water on the condenser and watch the gauges for any movement. I have a new condenser arriving tomorrow that I plan to install. The only part left to replace, I believe, is the compressor. The above chart is not specific to my vehicle, but is a general chart available online. I have an AllData subscription for this car and will check there if they have a specific chart.
I can definitely try this jumper procedure. Will this tell me that the switch is bad? Currently, my techstream software isn’t showing any error codes so i’m thinking the switch is okay.
The point of using the jumper wire on the low side switch isn’t so much to test the switch, it is to keep the compressor engaged so you can get good longer term readings. at 81 degrees ambient temp, if your system is working properly, it will begin cycle on and off quickly, not allowing you to really get a good look at what is happening.
Then you can do tests like air flow over condenser, water on condenser, etc.
as for the blend door concern- you can purchase pliers at Harbor Freight that will pinch off your heater hoses going into the heater core. This will stop coolant flow, and will be a good test on the blend door theory.
and I dare say, the amount of money you have tossed at this thing would have likely been considerably cheaper had you taken it to a reputable shop in the first place. and I sincerely hope you are recovering the r134 out of your system properly each time you open it up.
Yes, @eddo’s explanation is correct. Jumping the switch is to give you control over the system operation and an instant emergency cut off if there is a problem.
This video gives a good sense of how to diagnose what seems the opposite pressure condition you have but a likely identical part that has failed.
and in the case of that switch the mechanic mentions the 2 wire connection back at the expansion valve at that seems certain to be the low pressure cut off that only allows the compressor to run when there is adequate pressure, usually about 28 psi on common domestic vehicles.
The mechanic does seem to be knowledgeable and insightful in diagnosing the problem. But again, as @eddo mentioned, it is possible to spend more money throwing parts at a problem than it would have cost to have a professional to repair it.
and sometimes things just don’t make any sense at all.
I had a system that would work perfect in the shop, and about once a week would start blowing warm air. I couldn’t replicate it in the shop, at all- so I had to start tossing parts at it. Mine turned out to be a hose that had to be broken on the inside up under the truck. It wasn’t leaking refrigerant, but apparently, and at random times, the inside of the hose would just collapse enough to block flow- causing the condition. Because it was seemingly random, I could never find it. That truck has a whole new a/c system now, though, lol
Sometimes you have no choice but to throw parts at a problem @eddo. No matter how I explained it to customers that replacing the ignition module to hopefully cure an intermittent no start was much cheaper than paying for the time to pinpoint the cause they were disgusted when a few days later the engine failed to start with after spending $200. At least when it’s your own vehicle that gives you all the grief you don’t have to answer to a disgusted customer.
Every time I read aAC problem here I wonder what the chances are that the problem will be solved any time soon for less than a dealer would charge to fix it. I felt somewhat encouraged by the OP’s willingness to get his hands on a good set of gauges and do some investigation and hopefully this will turn out well. AC operation just doesn’t make sense to most people though.
I’m only about $200 in parts so far plus my time. I think that’s a heck of a lot better than what any shop would charge. Before I replaced the condenser I showered it with the hose and the pressure on high and low dropped. Mostly on the high side around 80-100. I went ahead and changed the condenser tonight. The readings appear okay for a 70 degree cool evening. It’s cooling down to 40 but only in low ac setting. When I put it on max cool it raises up to 60. Someone please explain.
Failing compressor was suspect from the beginning of the thread IMHO.
Now, with all new and shiny parts installed, if compressor is spewing any contaminants in the process of aging/destruction, all the system has to be carefully cleaned again as installing new compressor to inherit the contaminants in the system would be less than ideal.
My mechanic replaced the compressor for me today. 90 degree hot summer day. AC was blowing 60 on the way home on high. It dropped to 45 with the fan on low setting.
Good morning all,
As I mentioned earlier, the new compressor was still cranking out 60 ish degree air on a hot summer day. It has never really improved from that and the wife said on her 2 hour drive home from Louisiana last week the ac was even cutting off and not blowing cool at all! I’m at my wits end so I decided to take it to a local shop so they could vacuum and refill it ‘professionally’. They did so and nothing new. They did tell me that they only filled it to 24 oz per their fancy new snap on ac machine. Per the sticker under the hood, it should have a min of 1.59 oz or 25.4 oz. I took it back today and they checked it out and said no leaks (they put dye in it last week) and their machine is saying the correct amount of freon is in it. I don’t want to get rid of the truck as it is great otherwise, but does anyone have any other ideas?! The shop stated the fans were working properly. Should I insist they had 2 more oz to it?
Take the vehicle to a highly-rated independent A/C specialty shop (or a mechanic that has experience with HVAC work), and pay them to diagnose the problem and pay them to properly fix the problem.
Well, quick update. I noticed on Sunday the ac fan wasn’t turning on so I just knew that was the problem! I ordered a new fan assembly and installed it tonight. Same problems!!! Ac blows as cool as 45 on low ish fan setting but on high it only cools to around 65. I’m done fooling with this car! Any ideas?? I found this post on car talk with a similar issue and suggestions said maybe the Freon was low. I suspected it of being low ever since the shop recharged it so I added about 3 oz tonight. No difference.
I will say the compressor is always running. It doesn’t cycle.
See pics below with fan settings on high and low. Also see pics of gauges with current 73 degree temp.
