A/C R134a pressures too high. I'm lost. Ideas? - PeachParts Mercedes-Benz Forum

ps2cho · #1 05-16-2012, 07:08 PM

Hey guys,

Replaced my Receiver/Drier today while I decided to evacuate and recharge because I believed I had air in the lines because high side pressures were almost hitting 400psi!!

So I replaced the R/D, resealed everything, evacuated for 45mins held at 26 inHg, turned compressor off for 10mins and came back to find everything dead on where I left it...

So no leaks. (no leaks prior either)

r134a needs 900mg for W124 = ~32oz.

I put 1 + 1/2 12oz cans in so ~20oz (it wouldn't take the 2nd can full at all even after 20mins 2000rpm and putting the can in hot water)
Ambient Temperature: 104F
After this my pressures are:
Low: 59psi
High: 360psi

Aux fans are on full blast. I ended up re-evacuating AGAIN to make sure I didn't make a mistake with air getting in and same issue.

Why are my pressures SO high? Somethings wrong.

platt-deutsch · #2 05-16-2012, 07:40 PM

Plugged condensor coil ? Try a water hose running over the condensor coil to cool it and see if it acts different. Is the outlet of the condensor hot or is it about ambiant plus 20 deg? I had one that the bugs had completly plugged..

ps2cho · #3 05-16-2012, 07:48 PM

That's what I thought at first, but I've got condensor coil cleaner and hosed it off...no change.

I do notice that with A/C on even on the freeway, my engine temperatures raise about 5-7C. Could it be possible I have crap inside the condenser? Maybe liquids?

I have some basic knowledge on how to charge and evacuate, but problem-wise, not too experienced. Not sure where to start really.

platt-deutsch · #4 05-16-2012, 07:54 PM

If inside of cond. coil is plugged the outlet would be awful hot unless it is plugged completly.. When system is open can you blow good volume of air thru it? Could there be a strainer on the input of the exp. valve that is plugged? I dunno its a odd problem..

ps2cho · #5 05-16-2012, 08:01 PM

Its gotta be something blocked.

I verified it was pulling vacuum because I pushed a screwdriver on the shrader valve, and it had suction, so the system is EMPTY. Now, why does 20oz of 134a (effectively 3/5ths of the required amount) make the pressures shoot through the roof. The system STILL needs another full 12oz, but there is no way it can take it.

Could the expansion valve be plugged or open maybe?

I don't want to start evacuating everything again unless we are sure its the condenser. Or I guess a foolproof method is to flush both evaporator, condenser and replace TXV?

platt-deutsch · #6 05-16-2012, 08:12 PM

If you had a port on the line feeding the exp. valve it would be easy but I doubt there is one.. It could be a bad exp. valve that wont open but if that was so, I would think the low side pressure would be very low or in vaccuum . It sure sounds like a cond. coil problem.. Wonder if the cond. coil is slugged with oil? opening the system and blowing air or Nitrogen thru it would tell you that.. I dunno... I am about out of suggestions.. When you find the problem, I sure would like to know what it was..

gmercoleza · #7 05-16-2012, 09:41 PM

Quote:

(it wouldn't take the 2nd can full at all even after 20mins 2000rpm and putting the can in hot water)

This to me is a big red flag. My AC capacity guide tells me the 300E of that era took about 35 oz. of R12. The system should have no problem sucking in 80 percent of that in R134a (28 oz.).

There's some info missing in this thread. Is it indeed a W124? Is it a R134a conversion? Was the conversion performed properly, eg. components flushed, oil changed, etc.?

p7fan · #8 05-16-2012, 10:08 PM

Sounds like a txv. Opening everything up to flush/blow out will verify where your restriction is....but then it has be all be sealed back up again. My money is on the valve.

duxthe1 · #9 05-16-2012, 10:37 PM

Sounds like it is too full of oil. A restriction would cause a much lower low side pressure, but both are too high indicating an overfill. Since it isn't overfull of refrigerant, I could only suspect it is too full of oil.

ps2cho · #10 05-16-2012, 10:51 PM

Sounds like I need to blow out the entire system and replace TXV then...
Resolves all ideas in this thread! Since the expansion valve is so cheap, its probably worth it.

History:

I had my dad's friend convert it to r134a back in 2006 (before I realized I should have stuck with R12), and its worked fine since. No sealants, no leaks, its ran super smooth. When I came out here to Arizona though, A/C needs to be top notch, so that is probably why I haven't noticed it because its never been pushed.

Its my 300TE, sorry thought I included that on original post.

just-n-time · #11 05-16-2012, 11:46 PM

I would look at the system needing a flush, break down in units and flush, and do not for get the expansion valve if your car has one, some have gone to the reed valve and that will stop up from the black death.

Merkey · #12 05-17-2012, 05:40 AM

Pscho, it was already on 134a when you bought it, it was just low.

engatwork · #13 05-17-2012, 08:35 AM

Quote:

A restriction would cause a much lower low side pressure

Yep, I had a Honda in one time that the lines were plugged on. The low side actually went to 0 and I did not see what the hi side got to but it did lift the relief valve on the compressor

.

Were are you moving from?

ps2cho · #14 05-17-2012, 12:15 PM

Not sure if this gives any indication too, but at 2000rpm low side gets about 40psi and high side ~370psi

Zulfiqar · #15 05-17-2012, 05:56 PM

it looks like the condenser is not shedding heat at all, overcharged with oil?? You need to aim the condenser outlet with an infrared thermometer to see how hot is that line. at this pressure it should be blazing hot.