October AC HELP

[khamul02]

I know it is crazy but... just charging my AC for the first time this year and getting strange results. Put 3 cans in and had the same thing happen. I pulled a vacuum and it held but after a can goes into the system the low side returns to a negative pressure. I would first guess my gauges are screwy but the vent temps haven't dropped a degree. Very strange.

Is some failed? Compressor is coming on and high side seems to be stuck at around 100psi no matter what is going on.

I completely rebuilt the AC in the other car 7 years ago... and have yet to recharge that one.... That work sucks though but maybe that is where I'm at with this one.

[Bob Kontak]

There are a lot of AC pros here. I will say my piece but note a smarter person may contradict me.

Your compressor is sucking a vacuum on the low or suction side. It normally sucks then blows but there is usually some substance to suck on (vaporized refrigerant).

The system is supposed to spray liquid refrigerant through the expansion valve into the evaporator. The thermal expansion valve (TXV) is connected to the evaporator and is like the nozzle on the end of a spray can.

If there is a blockage on the pressure (discharge) side of the compressor that won't allow refrigerant to flow into the low side (through the TVX) then there is nothing much for the compressor to suck in and compress. It just sucks on the air in the low side lines, creating a vacuum.

My bet is that the TVX is clogged.

In a perfect world you have a mouse tooth stuck in the TVX. You change it out and for $25 you are back in business.

Meticulous guys ask why did it clog and best to flush the system and replace the receiver/dryer since the system will be open and for under $100, why not.

See 2:00 in on this Scotty Kilmer video.

https://www.youtube.com/watch?v=80jSH8VQZms

[khamul02]

I think ... oddly enough.. I have an unused expansion valve and dryer from other install... went with a procooler. The issue is .. do you limp along like I (and most 911 owners) have for the last few years or just gut the whole thing and start over.... uggggggg.

[Bob Kontak]

Well, you are in Mississippi..................In Ohio you can gain some comfort from a well functioning stock system. Heat is real down there.

[Ronnie's.930]

Originally Posted by Bob Kontak

. . . It normally sucks then blows but there is usually some substance to suck on . . .

Dude, seriously?!?!

[Bob Kontak]

Originally Posted by Ronnie's.930

Dude, seriously?!?!

No homo, Batch.

[khamul02]

terrible .... that I didn't catch that

[kuehl]

Khamul,
Are the 3 cans 12 or 16 oz?
When you noted 3 cans, 0 low 100 high, what was the outside air temp approx?

A normally running AC system ...evaporator outlet pipe will be sweaty to frost and the inlet to TEV will be warm to hot.

[khamul02]

12oz. I added 2 with zero movement in temperature or pressure (other than from shaking the can and getting a spike). Added another with the same results. Outside temp was probably around 90. The only thing that was cool was the hose going into the compressor from the gauges. The video makes a lot of sense. Thoughts?

[kuehl]

Flushing a system? Sure. Smart thing to do. You will spend about 8 to 10 hours to do it correctly and depending upon the AC flush method you use (16 oz aerosol or 1 gallon plus flush sprayer) figure $100 to $150 in materials.
Each of the 5 stock hoses, one end has to be below gravity and none can have hose paths that are above it. You will need to remove the evaporator, take off the TEV to flush the evap. You will be flushing the five hoses, 2 condensers and evap. You do not flush the compressor, TEV or drier. Replace all the o-rings and drier, replace the refrigerant oil. Might as well disassemble the compressor and inspect its internals, toss in a new seal kit if things look good, if not then a new compressor.

Alternatively, you could take a few cotton q-tips, swab inside of a few AC hose ends to check for contamination. Or, just replace the stock hoses since they permeate refrigerant (leak) anyway and replace with barrier hoses. Remove the TEV and inspect its inlet and outlet for debris, do a blow through test.


TEV Symptoms of a TEV issue can be either excessive low side or negative pressure with excessive high side (a closed or clogged TEV). Or, higher than normal low side pressure (an open TEV). Provided the system was evacuated properly and you have the correct amount of refrigerant in the system; IE. if the original R12 amount was 47 oz, then you should be putting in about 40 oz of R134a.

Here is where most DIY run into issues:
A) Inadequate evacuation: there is still ambient gases (air) in the system and moisture is freezing inside the TEV. This could cause the TEV appear either stuck closed or stuck open.
B) Inaccurate charge weight amount of refrigerant. Too little or too much. And, when swapping cans of refrigerant air was introduced into the hose line.
C) Not understanding hose the service gauge manifold valves work; valve rather than closed when taking gauge readings.
D) Using mixing or adding PAG rather than Ester oil into a system that was running R12 mineral oil.
E) Not applying the relationship between pressures and temperatures; use a P&T refrigerant chart to determine what the high side pressure should be at a given ambient (outside) air temp.
F) Putting in a leak sealant into to a system; causes more problems than its worth.
G) Not taking into account previous work that was done on the system; type of refrigerant oil, modifications, etc.
H) Not inspecting and testing system components: compressor clutch and its ability to pump, thermostat function, front condenser fan motor, evaporator condition, proper evacuation and leak down test.
I) Not testing your vacuum pumps capability or testing your service manifold and and hose set prior to commencing work.
J) Failure to have the deck lid laying down when testing.

Where To Start?
36 oz of R134a at 90F ambient. Let's assume first that there are no mechanical issues with the system components, the TEV is okay. Your high side pressure at idle, at 90F, should have been near 238. Start over again. Remove refrigerant. Remove refrigerant line to the TEV. If the weather is warm you should be able to blow "some" air through it. If so re-attach with a new o-ring. Install a new drier with o-rings. Evacuate properly and charge with 36 to 39 oz R134a. Let the system run for 10 minutes and then record at idle when the compressor clutch is engaged: ambient temp outside, low side and high side pressure, observation of evaporator outlet pipe as to (warm, sweating or frosty), observation of drier to TEV hose (warm or hot).

AC Help