Hello,

The AC on my xk8 doesn't work. I did my share of reading - low pressure, high pressure, condensor, evaporator, value etc. and collected some data. I'm missing the practical application of being able to interpret the data I see. Hoping someone can help me with that.

First my mistakes, I tried to charge the AC without understanding the parts that wasn't a great idea, but I think I'm ok. Here is the data I collected.

Outside temperature : ~80
Static pressure : ~ 55 . This was probably ~45 before I like recharged it without checking

Operational pressure : Low side 3-5 high side ~80
Temperature reading from the center vent with AC operational ~85 (or close to outside temperature)
Both view the change in pressure and a hearing a loud click, the compressor is engaged. Any, thoughts on how I could proceed?

Thanks
-Bhaskar

 

Static pressure image



Operational pressure

 

Were you charging it with the engine running and ac on?

 

Yep. I looked at the pressure initially with everything of and the guages looked ok. I didn't charge it at the time but later in a moment of madness, looked at the pressure when the engine was running and the AC was on thought the pressure was low. Three quick squeezes to charge but immediately realized what I had done and stopped, but the damage might have been done

 

Both your low side and high side pressures are low. You certainly don't have excessive refrigerant in the system. I see no reason why you shouldn't continue charging of the system until you get 40 PSI (temperature corrected) on the low side.

if you're refrigerant pressures were previously correct before you charged it and then everything dropped where they are now, then yes, you may have blown a seal somewhere in the system.

Nothing that you are showing indicates that you damaged the compressor itself though.

 

Thank you for the response Martin much appreciated.. Based on your response I didn't blow a seal yet

I am going over the temperature pressure graphs from the workshop manual.

I am interpreting this as at ambient temperature (when system is not in operation) a high side pressure of ~170 psi (it is currently around 80F here)

I am interpreting this as at evaporator temperature (when system IS in operation) a low side pressure of approximately 38 psi (as you already pointed out), and a temperature in the 40-43 F range.

I will try this out tomorrow. If anyone sees this and notices something wrong, please feel free to point that out.

 

I usually shoot for around 28-30 psi on the low side, and 2.0 to 2.2 x the ambient temp on the high side, with the engine running about 1500 rpm, fan on high, temp set to low, window open. This should get you in the 40 degree area on the middle vent dash. Mine runs about 40 in the garage, but can run down to 38 on the hwy.

 

Thanks darbysan.

Update: I charged to ~30 psi on the low side, the high side ended up at 175 psi in the 2.4 to 2.5 x range of outside temperature today.



But when I compare it to the performance of your AC I'm well short. Much better and I can ride the car around on hot days, but the number look work.
The in garage temperature was 57 F. I drove the car around not on the highway locally, and it settled around 55 F. Any thoughts on how I can squeeze out a little better performance?

 

Just for comparison, my gauges are now reading closer to 20 on the low and 250-275 high , but it is a lot hotter here. Going a little lower on yours, with a little higher pressure, may help ( adding R134a should cause this).

R134a is very finicky about just the right amount. 1-2 oz too much or too little can affect the performance. At this point, I would suggest adding just a little at a time ( maybe an oz) and then let it settle in for 5 minutes or so running to see where it goes. If the temp goes down, keep adding just a little until it stops going down and starts to rise. If you get too much in, it's simple to just "lose" a little out of the hose. One thing to remember- the hose has air in it, which may contain moisture. You need to let a little of the freon escape from the yellow hose at the manifold before adding (and the blue hose when attaching), or you can introduce moisture and air into the system. Moisture can cause the evaporator to freeze up ( don't think you are that cold yet).

If you can't sneak up on it as I suggested in the first paragraph, this would be the next way to go. Worst case ( and best overall result) is to remove all the freon, vacuum down the system for 30-45 minutes to remove any moisture, and then fill with the correct amount of freon based on weight. Then you know you have the correct amount of R134a in the system. R134a is cheap enough now that this is a practical solution ( $5 at Walmart). Even this process might require a little "tweaking" at the end, due to loss from attaching the cans, etc.

 

Is the low side 30 psi the proper temperature corrected charge for your weather? That seems awfully low.

 

mhminnich, based on the graphs LP pressure under operation of 30 is in the range, I calculated a high LP of about 36. This time around I didn't check what the LP static pressure was, previously it was around 55. I will report back on where I ended up once I get an opportunity to check.
darbysan, followed your suggested technique and ended up in the 48-50 F range. I stopped at this point, didn't want to push my luck further and was happy with the cooling. Wife approved , previously she wasn't willing to go in this car due to the AirConn.

Final numbers
Outside temperature : 82 F / 27 C
LP : 31 psi
HP : 220 psi
temp : 48 F
Static pressure : TBD - will edit later.

mhminnich & darbysan - appreciate the help, thank you.

 

Glad it's getting better. Static pressure doesn't mean too much. Static High and low sides should be about equal, and it should be about the same as ambient temp. That being said, you can have static pressures at the right pressure, but not have enough R134a in the system, so it doesn't tell too much. About the only time static pressure gives me any indication is if it is well below ambient- then I know it is low on refrigerant.

You can measure the temp of the pipe next to the Blue connector. It should be cold to the touch when running ( may even condense over). If you look at your AC gauge, you can see an inner ring for R134a that is temp. At 30 PSI it's about 35f. If you read the temp on your low gauge, then measure the temp on the Blue pipe where it is cold, you are looking for about 15 degrees difference ( Pipe being warmer than the gauge). This is the Superheat calculation. More than 15- too much R134a. Less than 15, too little. I'm just starting to use this calculation for my installs ( just bought a fancy set of gauges ) so I'm still learning how to use this. Might give you one more point of info...

 

Very interesting. I've never heard of this method before your post. I'll look forward to updates!

 

The AC fill valve should have a screw-on cover indicating the type of refrigerant stamped on it.
Not sure where it is exactly but should be easily accessible.