Need some experienced A/C diagnosis
 

So I am having a problem with my 300TE's A/C...
I think there is a blockage in the system somewhere, but I need help diagnosing this first.

I evacuate the system, and vacuum down to ~29 hg. The problem is that with only 12oz of refrigerant, I am getting 45/320 psi lo/hi. (25/380 at 1500rpm).
That is only a 1/3rd of the recommended capacity for r134a (the recommended is ~28oz). Why would my pressures be so high after only ONE can? The only thing I can think of is that there is a blockage?

Could there be anything else that could be causing this? I'm purging the lines of air before I begin and vacuum held fine for 30mins after I shut off the valves.
I need some help diagnosing here its driving me crazy!!!
Is there a specific test I can perform so I don't have to waste hours and hours swapping parts unnecessarily?

Using R134a you need to calculate by the ambient air temp.

At 90F, using R134a, you should be seeing 45-55 psi on the low side and 250-270 psi on the high side.

It appears you could have a orifice tube/expansion valve problem.

Evacuate, replace, flush, vacuum and re-fill.

Ain't automotive A/C fun!

Feel the high side tubing with the system running. It should be quite hot to the touch all the way to the txv. If you find a spot where it turns cold or cool, there is your blockage.

Possible the drier desiccant bag contents have plugged up the orifice in the drier.

Remove drier and blow through with air line. Clear ? Then blow through rest of system isolating the hi side and lo side as two separate systems.

Possible TXV has jammed closed, nearly closed or blocked..

Ran mine with Duracool up to 200,000 miles. Duracool may not be legal where you are.

FYI : Holding a vacuum is no indication it will hold pressure.



.

.

If there was a restriction, you should be able to find it easily. Normally it will produce an ice ball, and you will have super high high side, and or super low low side.

My experience with mb Ac systems is that you should just charge it by weight and don't look at the gauges. My vague recollection of my 300e was that the pressures were high after about half the r12 was in. I just stuck to the scale and I had perfect Ac after.

I was experiencing the same thing, except with propane. Then I said forget the propane something isn't right. So we put the r134 back in, but we were going based on the gauges and pressures were still high. My friend decided that we should stop because the pressures were too high on the high side. When I left his place the temp was about 110°F, so I ended up going to Wal-Mart after picking up my son and just decided to purchase 2 of the 505 gram cans of 134 and I just charged the system until it got cold. With the outside temp the way it was I pretty much had nothing to lose and damaging a compressor was the least of my worries as I would just buy a new one. Sure enough after emptying the first can, there was no change, then half way through the second can the temps dropped at the vent. I added nearly the entire second can, save for about 2 - 3 grams and now my ac is better than I can remember. My vent temps are well below 60°F, I'd say maybe 45°-50° at the vents. Of course this isn't nearly as cold as what I was getting with the propane when then system was working properly, but I will not revisit messing with my ac system until the fall. So, I am in agreement with Lorrainefurniture, ignore the gauges, matter of fact, ignore the weight to a certain extent and fill the system until you notice a change. Obviously the original system was designed for about 1000 grams of refrigerant so you don't want to go past that and not have any change, but I'd say give it a shot, especially since I'm sure the AZ heat is just as intense there as it is here. Good luck and let us know.

Ignoring the pressures is asking for trouble. If I just willy nilly charged by weight then I'll have the compressor blow a seal as pressures would easily get above 450psi...you MUST use gauges, every time!

Thanks for the line info. I ordered a Infrared Temp Gun and I'll get a readout across all the lines and see what it shows and reply back at that time.

Charging by weight is the only truly accurate way of recharging a system. The car should never get pressures that high, there is a cutout switch on the high pressure line for those situations. Also, the fans should be running full speed after 350 psi.

You keep thinking that because you had 350 psi with 12 oz of r12 in , that you will have 3x the pressure with 3x the refrigerant in. This is not true.

The system is already pumping at capacity the moment there is enough refrigerant in there to liquify. Remember, the refrigerant is the stuff that absorbs the heat from the cabin. With only 12 oz in, there is not enough for you to notice a difference. The system is is working at full pressure, just not enough volume to make a difference. Just charge the system 2.2 lbs, or 1 kilo, and be done with it.

Probed with the temp sensor today, no cold areas or anything that seemed odd. All the high side hoses were too hot to touch, and the low side was mediocre cold at best...
Condenser inlet and outlet temps show a 80F drop, so the fans are shedding heat fine and its not a blockage in the condenser...the pressure is just off the charts.

Here's proof the pressures keep going up and up. I added about another 1/2 a can in. I stopped because with whatever is going on, is not following your theory.

This is at 1500rpm with both aux fans going full speed. Ambient temp right now is 98F.
Vent temps were showing 63F.

http://w124-zone.com/downloads/photo...cpressures.jpg

The logical explanation is that the condenser is not properly shedding heat. Make sure that the aux fans are turning the correct rotation. For about the last decade the replacement fans come with the wiring backwards in the plug. I've seen plenty of fans spinning the wrong way.

What was the pressure at idle?

At 40/ 440, looks like there is a restriction somewhere. The expansion valve is a common place to clog.

I know you said you vacuumed down to -29, but those numbers could be also indicative of air in the system. When you vacuumed down the system did you do it for at least 15 - 30 mins on low and hi side? Also, before you started charging, did you crack the yellow feed hose first to purge the air out and let the r134 fill up the hose before you introduced the refrigerant into the system? I would say vac the system down again and follow the recommended charging protocol. Or, try getting the rpms up to about 2500 and see where you are at with ac vent temp and the high and low side pressure. If it stabilizes at the higher rpm and then goes back up, you could have a problem with the compressor not properly compressing the refrigerant.
Also, check out this attachment. Good luck.

at 450 psig with runnign system your liquid line should be extremely hot, try dousing the condenser with running water and see if it helps.

In one instance in a another brand car I was repairing this behaviour was caused by a faulty expansion valve - its high side was reaching 400 psi while the low side was at 30 and going towards 20 when revved.

It maybe that you have a lot of oil in the system.

I agree Charging a system by other means than a recommended required Weight


is only charging to the systems limitations. Inefficient condenser , TX valve not fully opening. sensor out of speck. Vacuum??? if you don't use a vacu stat YOU ARE ONLY GUESSING Yes the gauge says you have a good vacuum , But in reality without a vac u stat you would be surprised at how much you could be off a SAFE vacuum.
Remember what the vacuum is doing . Not sucking crap out the system . Only lowering atmospheric pressure to allow moisture to BOIL off and out the system. If you want to blow the lines NITROGEN not your air compressor. AIR is Moisture it just doesn't mix.
Pressure test a home A/C with air . You will have a hole in the ground where it once used to be.

Eh ?



.

Basically moisture from compressed air will destroy a central air system in short order. I personally have never seen one leave a crater, I shire would like to see it.

Mobile systems are more tolerant to moisture, but sweeping the system with nitrogen helps blow out any moisture that was boiled out during vacuum. You really wouldn't think its there, but with a vacuum gauge you can really tell.

Sorry I didn't finish explaining .
I was only referring to what a bad mix AIR is with A/C systems .
An example is AIR/Compressed air being used for a leak check (PREASURISING A SYSTEM) OR flushing a line if that air meets and mixes with the compressor oil . Boom can occur. Always nitrogen, clean safe, inert . added benefit it helps absorb MOISTURE in the system. If a system has been open for a prolonged time or LOW on refrigerant it can run in a Vacuum where AIR can enter , If air enters so does moisture. Only 2 good ways to remove moisture .1 use nitrogen and allow it to stay long enough in the system to absorb, then purge it off. DO NOT run the system with nitrogen inside. 2 A good vacuum . IT Can only be measured with a vac u stat. A good Vacuum is 1000 microns and lower. the ideal vacuum is 500 microns and lower. This unfortunately can not be measured by gauges.
Also remember with car A/C systems that were not designed for 134A from manufacture The condenser just cant do the job properly . Meaning the condenser needs to be a lot larger or the refrigerant charge lower. A poor compromise . TX valves should always be changed if a system changes refrigerant . More flow is required with a LESS yielding refrigerant . High head pressures are MOISTURE in the system, secondly Restrictions. Or a inefficient condenser, Remember also oil migrates around the system with the refrigerant. DO NOT blow it to places in the system where it cant return unaided. Thank you for the link. a good read:) I am new to forums and still finding my way. No disrespect meant for anyone.

Just finished up -- it was either excess oil or a blockage. I flushed the entire high side from condenser to TVX and the evaporator. Replaced expansion valve and receiver drier.

and Success, or about the limit of R134a in my climate!....Definitely either flushed out excess oil or removed any blockage.

I got about 24-26oz estimate in. That is about 6oz short of what the factory manual states, but any higher was outside my comfort zone for pressures. In cooler climates I would have added more for sure. Final pressures 55psi low 375psi high. Ambient temp is 112F. Getting 48F out of the center vents on the quick drive I made. Rises to about 55F at idle. I expect on the freeway it'll get down to the low 40's.

I think that's about the limit of R134a in this climate! Either way it'll last me the rest of the summer and once I put the new evaporator, heater core, compressor RD/TXV and R12 in, I should see even lower vent temps and lower pressures.

Awesome. Thanks for the update.

Congrats! I agree with your assessment regarding the maximum efficiency of your system.

Are you suggesting that the compressor can auto ignite the oil in an a/c system ? or the gas, should you be using propane?

I think you ought to read this :Fuels and Chemicals - Auto Ignition Temperatures

These temperatures listed only exist inside a diesel engine and to start most diesels it is often only with the aid of glow plugs...ie: An ignition point.

I doubt any refrigerant pump can run at these temps'....and where would the ignition point be ?

The 'hole in the ground' sounds spurious.
.

I think he may be referring to the danger of oxygen + oil in an oxy-acetylene regulator/tanks setup, where pressures can be in thousands of psi. But we are talking air at 200 psi.

"By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere."

I was wondering if air can be used to do a poor man's "nitrogen" pressure test in a mobil AC system since it is 78% nitrogen. Is there a danger of an explosion with 21% oxygen and refrigerent oil pressurized to 200 psi? Gut feeling WAG tells me no.

Granted, some moisture (relative humidity dependent) will be introduced from ambient air, but since the dryer and TXV will be replaced and the system evacuated afterwards, whatever moisture introduced will be removed.

I vacuum the system for 5 hours or so on vehicles that have been open for some time. Blowing out the system with shop air is okay as long as you purge with refrigerant before charging.

The ox-acetylene sets potential to explode is well known, either due to fire or incompetent handling.https://youtu.be/iam27Mh1zu4



.

Holy smoke, that's some fireworks!

What do you use for a vac pump, single or dual stage? What vacuum level do you get it down to? What do you use for a vacuum gauge to see the level achieved?

Single stage commercial . Have calibrated gauge and at 1100 asl I see 29 inches. If you hold 29 for some time and run the engine to full temperature you can be sure that whatever minute amount of water vapor is in the system is absorbed by the desiccant....or so small a volume it will not ice anywhere..


.

Would you know if I run two vacuum pumps in series, would I be able to achieve lower vacuum levels than a single pump? I can rent (free) a single stage pump from Autozone, I can scrounge up a compressor from a house AC unit and run that in series.

I need to come up with some kind of digital vacuum gauge. They seem to start at $140 and up. This one reads in microns https://www.amazon.com/CPS-VG200-Digital-Vacuum-gauge/dp/B009AXGCSC?ie=UTF8&redirect=true&tag=gols-20

I don't care the units used. I can convert them Vacuum Pressure - Units Converter

I am buying one of these to play with, $20 shipped New SMC RS Vacuum Pressure Switch ZSE4B 01 26 Q | eBay

readouts in kPa, mm HG, psi and bar

[QUOTE=funola;3608741]Would you know if I run two vacuum pumps in series, would I be able to achieve lower vacuum levels than a single pump? .......................................................[UNQUOTE]

I would say no. Both pumps do the same thing so very low vacuum of 1 torr or better would not be attained. Even lab' rated vac' pumps only pull down to 5 torr.

You need very specialized ( read : Expensive.) equipment to pull a near pure vacuum.

I would say that is is impossible to pull a pure vacuum.


.


.

[QUOTE=dkveuro;3608748]I can have access to a vacuum pump used in a lab, problem is getting permission to wheel my car in there. And then explaining of why I need that sort of vacuum in my car A/C

btw - funola

I have lived in third world countries where resources were scarce, I regularly saw A/C work being done by pressure testing with a junked refrigerator compressor pushing air in the system.

It was good enough - cant say about longevity, usually A/Cs were taxed to the max as summer meant 120F in the shade.

There is no need for scientific grade equipment. A good vacuum gauge as listed above would be swell. Anything that holds under 500 microns is considered a tight system.

Really for automotive systems, under 800 is great.