Overheating issues

CyFi6

CyFi6

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Oct 11, 2007
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Well to be honest I am getting funky readings from my thermocouple and I am trying to figure out why. I'm not over analyzing it, I am just trying to figure out how it works. Why is it that the readings accuracy is affected by the DMM temperature?
I don't know why my pressures are the way they are, I am not familiar enough with refrigeration to know what is wrong. There are people telling me I may have evaporator freeze up, which doesn't make sense to me, but it is critical to know the evap temp if that is the case. I really don't know enough to confidently change any parts where I stand now. Again, I would love to take the car to someone competent but I know where that will go, Ive done it... Anything aftermarket on my car gets blamed as the issue (Last time, they blamed my STOCK intercooler for a lack of proper airflow, then after I told them it was factory about 5 times they moved to the radiator and said that was the cause). I really don't want to downgrade to a stock radiator only to find it didn't fix a thing.

Right now I know I have low suction pressures, and I know at times, I have high head pressures. Could that be a TXV? I'm not 100% sure, could it be something else, very possibly. Getting the system evacuated, replacing the TXV, then getting the system charged is an expensive repair that at this point may or may not have any effect on my system.
 
jetjock

jetjock

creepy-ass cracka
Jul 11, 2005
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Improper refrigerant metering or a restriction after the TXV. No matter how much you want to dance around it the evap has to come out. Do it yourself and it won't be so bad.

Stop fussing over the meter. Odds are there's nothing wrong with it. Check that Type K with an ice/salt bath and boiling water if it makes you feel better. Frankly, T/Cs are not the best for this temp range but they're good enough.
 
CyFi6

CyFi6

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I have no problem pulling the evap trust me, I have pulled it out at least 5 times now, it's cake. The expensive part is buying the TXV (OEM is around $90) and having a shop recover and recharge my system. While I have the old TXV out, is there any way to functionally test it? I have already had all the lines off, unless there is some sort of newly formed restriction I don't see how there is a restriction in the suction line. How can I test for a suction line restriction with the system open?

Another question for you...I had the evaporator power flushed by the AC shop, is it still possible that the evap itself is the source of my restriction? It is one of the few items that has never actually been replaced.

The thermocouple reads fine when in a cup of ice water, but with the meter sitting on my dashboard in the sun, who knows, after all when the meter was cold it was majorly innacurate. Not really sure of any better method to measure the line temp while going down the road.
 
jetjock

jetjock

creepy-ass cracka
Jul 11, 2005
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Of course the evap could be at fault. Sounds more TXV though. Is the sensing bulb in the right place and properly insulated? Have you posted this issue on any of the AC forums?

Recovery and recharge isn't a big deal. Either buy a used recovery system or research building one. Lots of people do it. Many use an old refrigerator compressor. Or have the shop recover and you recharge.

Edit: If your evap was frozen the clutch wouldn't energize...
 
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CyFi6

CyFi6

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As much as I would like to have some equipment of my own it just isnt realistic with my current living situation. I really have no problem taking my car in for evac/charge if I know I am going to fix a problem, I just dont like the idea of doing all this only to throw a part at it with high hopes.

I figured if the evap was restricted, they would have let me know when I had it flushed, hmm, when I have things apart, how can tell if it is restricted? How can I tell if the lines contain a restriction?

Sensing bulb is properly affixed to the stock location with insulation wrap around it. Ive considered this as an issue, but in reality even if the bulb was hanging loose, low pressures would be raised rather than lowered as p1 pressure opens the valve.

I am looking in the EPC right now and I am a little confused.
Here you see the TXV for the 87 model
http://www.cygnusx1.net/Supra/Library/EPC/291410/catalog.aspx?F=8714&P=1
Here is my original TXV (first time I pulled the evap). The valve mounts horizontally, but in the EPC it is vertical. My original valve also had a sensing bulb, whereas the EPC shows a sensing coil. And yes, I thoroughly cleaned the evap coil!
p1736713_1.jpg


Now if I open up the 88 RHD "ARL" EPC I see what looks more like my original valve.
http://www.cygnusx1.net/Supra/Library/EPC/291210/catalog.aspx?F=8714&P=1

Any idea whats up with that?
 
CyFi6

CyFi6

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Hmm, easier said than done lol. I'm not sure if it is possible or not to pull just the lower half of the evaporator case off while in car. At this point, since I will be pulling the EVAP I am fine with replacing the TXV (still don't know which part number to get), but is there any way to check the evaporator itself and the suction line for restrictions(already checked visually)?

Oh, and about the frozen evap. The guy that was telling me this was suggesting I had an electrical issue preventing the clutch from releasing. Given all the other information though that really doesn't make sense to me (still though, its coming from someone who knows much more about AC than me).

Thanks
 
jetjock

jetjock

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Jul 11, 2005
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That it's easier said than done is exactly why I didn't suggest it. As far as the clutch failing to disengage I suppose that's possible. The evap thermistor or AC amplifier would have to fail though. Pretty unlikely. Besides, even of that were to happen it can't be the root cause of your problem.
 
CyFi6

CyFi6

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If anyone can shed some light on which expansion valve part number I need that would be great, going to head to the dealer tomorrow and hopefully get this thing changed asap. If nothing else, I will just ask for the expansion valve for my VIN.

I suppose if I blow through the evaporator with shop air, there shouldn't be much resistance(though I will have to make sure I measure how much oil comes out)? And maybe unbolt the suction line from the compressor and blow from the firewall all the way through making sure it isn't restricted? Not really sure how else to check it. I will go over it once more looking for cold spots along the suction line with the system running. I am also going to rent a vacuum pump and pull a really good/long vacuum on the system to be sure no moisture or air is left in the system before I get it charged.
 
3p141592654

3p141592654

90T
Oct 11, 2005
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LOL, who said anything about it having to be easy! If you think that in-car testing is hard, try testing it on the bench. You'll need a source of compressed nitrogen, regulator, manifold gauge set modified to instrument the TXV, plus some hot and cold baths and conversion data for the valve itself.

Also, something else I noticed that was interesting...every time I would come back to an idle and compressor speed would slow down, the suction line temp got about 10 degrees colder for a short length of maybe 10 seconds, then rose back up. Why is that? Was thinking maybe the blower speed was reduced when coming to idle, but even if I turned the blower to med speed the suction line temp wouldn't drop that quickly.
Click to expand...

Could be you are seeing the TXV regulating the refrigerant, but perhaps it is not the correct valve for this application. I think your best bet is to go OEM.
 
CyFi6

CyFi6

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I will check tomorrow, I am going to use my Raytek though hopefully it is accurate enough (can't check it while driving either). I would expect to see slightly high subcooling because of a lack of refrigerant flow, correct?
 
jetjock

jetjock

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Jul 11, 2005
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The Raytek isn't the best idea but if you're going to use it be mindful of emissivity. If required use a black tape where measurements are taken. I'd use the T/C or at least compare the two. Driving has never been needed. Just run the car at fast idle with the windows open, AC @ 65, blower on medium. Allow the system to stabilize for 15 minutes then record pressures, subcooling, and superheat.
 
CyFi6

CyFi6

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OK JJ I did it exactly as you said. AC, med blower, recirc, windows open, 2100 RPM for 15 min. Heres what I got

Ambient temp: Around 105, pavement measured at 155 Deg F

High side: 260 PSI (245 w/hood open)
Low side: 11 PSI
Vent: 54 Deg (51 w/hood open)
Suc Line temp: 84 Deg according to my thermocouple
Liquid line temp: 151 Deg according to IR gun(143 deg w/hood open, bubbles seem apparent in sight glass, though very hard to tell)

Subcool: ~9 Deg
Superheat: 79 Deg

Even made a couple videos to show the fan operation etc I will post when they upload
 
CyFi6

CyFi6

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jetjock

jetjock

creepy-ass cracka
Jul 11, 2005
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Redacted per Title 18 USC Section 798
155 eh? Now you know why pilots fret about long taxi times and why most tire failures occur on the departure roll.

Assuming you're not shy on refrigerant and it's not contaminated that all indicates an evap starved of refrigerant. Bad TXV, restriction in the liquid line, etc.
 
CyFi6

CyFi6

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Oct 11, 2007
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Haha yeah, and then we get rain 6 hours later...

What made you change your mind from a suction line restriction to a liquid line restriction?

Anyways, new OEM TXV, drier, and valve cores are on their way. Still open to any suggestions on how to find this restriction if it lies somewhere other than the TXV.
Anyone know by any chance if the OEM parts come with new o rings?

Thanks for all the help!
 
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