[E92_William]

Originally Posted by mainbearing

Looking at the 3 charts (post 18), those are for refrigerant cans with a low side gauge and are for "accumulator systems". If an expansion valve system is charged to 45-55 psi low side, then the system is way overcharged.

Looking at OP's numbers, I think 40 def F superheat is way too much. That tells me anyway the evaporator is starved of liquid refrigerant. I would try to find the coldest spot on the low side pipe near the expansion valve and double check.

There are no specs for supercool on the condenser side, but hvac industry looks for something like 10 F. On the condenser side 23 F supercool I would say is ok and probably slightly high (as well as the pressure).

OP can try running this setup for a while if the evap is down to 4 F (is that at idle?). My concern would be at higher rpms the high side might go through the roof and cause pressure relief of the refrigerant.

I do not know about flap position readings. I wonder if clamping off a heater hose can help test hot air leaks into the cold side.

Just want to make sure, you are measuring superheat temperature on the bigger pipe coming out of the expansion valve correct? If the subcooling decreased on the high side and if the low side temperature probe is on the >>liquid line<<, that would explain the higher "superheat" next to the expansion valve by roughly the same amount.

Also, is there frost on or near the expansion valve?

Additional info video:
https://www.youtube.com/watch?v=3uPLRWRWqaw

Well now it’s gotten to the point where the superheat will go through the roof just in operation. I put the probe at the thick pipe coming out of the txv which was cold to the touch almost freezing but not quite and wet but the readings show it gets to 120f or more even with an IR thermometer I’m using now. This is far too much to make sense for the textbook case of low refrigerant so I’m thinking it’s overfilled, oddly enough it works good still inside the car.

I think I’ll just need to bleed off refrigerant until this number stabilizes, what fucks me up is the lack of an official number for the superheat and subcool in this car as those change from car to car apparently. Gauges are still fine at 35 low and 250 high.

The odd thing is if I measure with the IR thermometer by where I have the high side probe I get a higher temp reading (20F+) which leads to a lower subcool, almost the same as the saturation. Now which is more accurate don’t think I’ll ever know.

[mainbearing]

IR thermometers are not accurate enough for taking pipe temperature. It is probably reading off ambient radiated heat anyway. A thermocouple with insulating tape on the pipe seems to be the standard method.

If the low side pipe by the expansion valve feels cold, then there is NO WAY the superheat is that high, even 40 F. 120 F superheat is impossible. So I think it is a measurement thing.

If the pressures are stable at 35/250, the evap core is around 4 F, and you are getting cold air. Well, I say leave well enough alone!! I would not add or remove refrigerant at this time.

[E92_William]

Originally Posted by mainbearing

IR thermometers are not accurate enough for taking pipe temperature. It is probably reading off ambient radiated heat anyway. A thermocouple with tape on the pipe seems to be the standard method.

If the low side pipe by the expansion valve feels cold, then there is NO WAY the superheat is that high, even 40 F. 120 F superheat is impossible. So I think it is a measurement thing.

If the pressures are stable at 35/250, the evap core is around 4 F, and you are getting cold air. Well, I say leave well enough alone!! I would not add or remove refrigerant at this time.

Well I hope you’re right regarding it being a measurement error. I’m using two sensors with probes for measuring pet enclosures taped one to each line so I figured they’d be accurate, I have to double check again tomorrow to be sure.

Pressures are indeed stable at that and the evap reads at around 8 at idle and can get to 4 when revving.

I was just concerned as those SC/SH numbers are indeed not normal and wouldn’t wanna grenade my compressor or another component from negligence.

Sure seems the fellas that told me not to fuck with it were onto something

[mainbearing]

Well, by touching the return pipe next to the expansion valve and feeling that it's COLD, you already checked the superheat, and it's probably close to the evap temp of 40 F or so and just a few degrees.

You can just use the scan tool to check high side pressure without connecting the manifold gauge set (which I avoided doing if I can). See how many bars at idle and 2000 rpms.

I think your subcooling measurement should be right on, from the picture.

[gbalthrop]

Originally Posted by mainbearing

Looking at the 3 charts (post 18), those are for refrigerant cans with a low side gauge and are for "accumulator systems". If an expansion valve system is charged to 45-55 psi low side, then the system is way overcharged...

Originally Posted by E92_William

... Gauges are still fine at 35 low and 250 high...

"KISS"!
Actually, the 3 charts LINKED at Post #18 are for Manifold Gauge Readings of correctly-charged system, WITHOUT regard to any other factor, such as Expansion Valve vs. Orifice Tube. READ the links PLEASE. ALL 3 Links show SAME pressures at 90F, OP's Stated Ambient Temp. That is 50 PSIG LOW side & 260 PSIG HIGH side.

IF Ambient Temp were 70F, Pressures should be: 35-40 LOW side & 145-160 HIGH side. As I read ALL 3 of the links, that suggests the HIGH side is ~ correct, but the LOW side is TOO LOW. A partially blocked/ restricted Expansion Valve is ONE possible cause of those pressure readings at that Ambient Temp.

If Evaporator Temp is closer to 0C first thing in morning with ~ 70F Ambient & cold engine, but Low Side is Still too LOW (per Chart), then there is likely reduced cooling capacity (heat absorption) by Evaporator coil due to "premature evaporation" where the "Return/ Left" side of coil is already gas. Remember, "Cooling" occurs when there is heat absorption, where Liquid Refrigerant is changing to Gas State: "Latent Heat of Vaporization".

ANYONE who wants to know some basics about Expansion Valves:
https://en.wikipedia.org/wiki/Thermal_expansion_valve

Hard to achieve "Lab Controlled Conditions" under the hood of a car on a warm day with engine running. While Superheat & Subcool measurements (if accurate) could be used to attain best "Heat Exchange" thru maximum use of "Latent Heat of Vaporization" to absorb cabin heat at the Evaporator coil, unless you have CONTROLLED Conditions with "Properly Calibrated" Temperature readings, AND a functioning ADJUSTABLE expansion Valve, WHAT are you going to do with that Data?

While you DON'T want to ruin your compressor by having R-134a Refrigerant in LIQUID State going back to compressor on Low Side, I don't see how a Thermocouple to measure Superheat is any more helpful than simply NOT exceeding the Low Side pressure value for the Ambient Temp. It is NOT "Keeping it Simple" to have to worry about the accuracy of the Temperature reading.

I'm a Dinosaur. I took Thermodynamics, Heat Transfer & Refrigeration courses as an engineering student in the 60's. I then became a Lawyer in general civil practice.

I have ALWAYS maintained my own auto A/C systems, R-12 & R-134a (conversions in the 90's). I have NEVER used a $hop & NEVER used "Superheat" or "Subcool" measurements/ calculations. If I were an automotive engineer Designing Expansion Valves or trying to maximize cooling by the Specifications/ Settings of those Valves, I would certainly have to learn MORE about Superheat & Subcool. Until THEN...
George

[E92_William]

AC in the wagon seemed to work fine today. It was around 95 and I was reading about 50 or lower with a vent thermometer, not perfect but I also vented a tiny bit yesterday in that superheat scare.. unfortunately couldn’t get live data because ISTA was having that time of the month.

Went to mess with the E92 since I knew it was kinda low, turns out the e92 can easily get down to 3-2C evaporator temps. However the vent temps are pretty much atmosphere, just a bit cooler. Leads me to believe the evaporator on it might be dirty as hell?

I wonder if it is related to the front stratification flap. Some fiddling around and when the AC is on MAX which it just blows ambient vent temp the flap is at 100%. However when I undo the MAX AC setting and set fan speed lower, the stratification flap begins to lower in percentage and the air gets a bit cooler. See last 2 pictures. This is a nice issue to have when I’m trying to sell the car in 2 days

[E92_William]

Well today I sorted the issue with the AC in the E92. It was blowing ambient and the evaporator was almost at freezing temp supposedly and would blow only slightly cold at low air speeds.

Well I went and put probes on all vents and the right vent was blowing abnormally colder than the others. Turns out in these cars if the system is low it will only blow cold to the right side if at all, which makes sense as that would be the side of the evaporator that is getting Freon evaporating but the other parts are empty.

So as I filled the system slowly more and more, I got the center vents to start blowing cold then the left ones and then adjusted the pressures to about 30-35 and 230-235 ish on the gauges and now the evaporator would stay normally at 6-7C. I didn’t fill it too much because I didn’t want to overservice the system and it’s blowing low F50s at idle and high to mid F40s at 2000RPM which is more than acceptable. I saw the issue on this thread:

https://www.e90post.com/forums/showthread.php?t=513648