A/C flush.
 

We have a very high high side system pressure of
400 psi at idle with only 1/2 pound of R-134.

Possible expansion valve stuck closed?

The system worked perfectly for several years
until the car was not driven for about 9 months.

Would an A/C flush provide relief?

Replace expansion valve?

Great vacuum >-30.

Thanks in advance,

Gerry

Gerry, I had this very same problem on my 85 AC. I changed the expansion valve and it fixed everything. I think mine was stuck or plugged. Anyway, was not hard to change out. Also, the expansion valve does not cost very much. Nick

+1

Pal's 89 930 had a blocked exp valve. 425 psi.

The tar tape is called prestite.

expansion valve and dryer.

I would only do a flush if the compressor went bad.

I did have one of the balls from a dryer come lose on another car and get stuck in the expansion valve.

it does kind of suck working in the smugglers box.
don't forget you have to remove the fan resistors from inside the passengers side to get the air box out.

Expansion valve.
 

No need to pull the evaporator.

The new valve is replaced from the top.

Thanks,

Gerry

Are you saying you pulled a vacuum and added 8 oz and your high is 400.....
what is the low side pressure?

If you put your hand on the hose fitting going to the TEV, is it warm, hot or cool.
And ditto on evap outlet hose fitting?

I did not check these temps.

Thanks,

Gerry

The system was working perfectly and it worked 9 months ago.

Did you decide to pull a vacuum and attempt to charge it after you noted an issue,
a part replacement or other?

Before you attempted to pull a vacuum and charge it with 8 oz, what was the system static pressure or operating pressures?

Pressures.
 

Here are the details.

After running the new system for 9 month to a year,
the car sat for about 8 months.

About 200 miles into new operation, the high side
compressor to rear condenser hose blew at the rear condenser interface.

I do have a high/low switch but it did not shut down
the system.

The hose connectors were replaced.

Post replacement, I pulled a good strong vacuum (>30 inches)
for four hours, and let it sit overnight.

The vacuum held-No degradation at all. (>30 inches).

Adding one can increased the high side beyond normal
at which time I took it to a local A/C shop.

With about one half pound of R-134, the gauges indicated
400 psi/HI 20 psi Low.

That hose must have seen a very high pressure,
or, a defective crimp.

As posted, I have a new expansion valve on the way.

Prior to this event, we had 45f air on a 90f freeway ambient temp.

I just disconnected existing expansion valve, along with the
the high side input and low side output to the existing
expansion valve, turn on the compressor for just a brief
second and noted a strong output hi side pressure from the pump.

Thanks for all,

Gerry

Adding one can increased the high side beyond normal
at which time I took it to a local A/C shop.

Did the AC shop pull a proper vacuum on the system before they attempted to charge?

Vaccum.
 

Yes, he did, as I watched the gauges.

He pulled the system down to greater than -30 inches and held.

The vacuum indicator was pegged.

At one pound, we were at 500 psi!

I had a look at the existing expansion valve,
but did not see any contamination.

It looks squeaky clean.

Because the car was running (at the smog test station)
when the hose failed, perhaps all of the oil went out
along with the refrigerant.

There had to be, or still is an obstruction of
some type in the system beyond the high side
input to expansion valve.

Either the low side, or the pump?

I should have the new valve from our host by Saturday.

Not related, but I passed smog...............

Thanks,

Gerry

A restriction can be anywhere from the inside the TEV, and going back all the way to the compressor outlet.

Disconnect the hose at the drier inlet (lower port on the drier) and disconnect the hose as the compressor outlet. Attempt to blow compressed air through that circuit.
Then ditto on the line from the drier outlet to the TEV (disconnect and blow air).

A TEV taken out off the evap, you should be able to blow air (low pressure, say simply 2 psi) through its inlet

Restriction.
 

I used the compressor (for just a very few seconds), to pressurize
the lines from the from the compressor high side
through the dryer, and saw some good pressure at the
output of the hose going to the TEV.

So, that should exonerate the line from the high side of the compressor,
all the way to the TEV input.

There does not seem to be any restriction on the high side up to the TEV.

Also, with the TEV removed, I was able to blow air bilaterally trough
both in/out of the TEV. (perhaps it needs to sense temperature to close?)

Although the low side pressure values seemed O.K.,
I'll try your recommendation for the low side going back to
the compressor tomorrow and report back.

According to the tech, the system demonstrated a high side blockage.

Thanks again,

Gerry

The sensing bulb (copper pigtail attached to top of evaporator outlet pipe) throttles the TEV; opening and closing. As the evaporator outlet temperature rises the TEV opens, as the temperature drops the TEV closes; however TEV's never fully close. You could test the flow rate (air moving through the TEV) by submersing the sensing bulb in ice cold water and then warming with your hand.

For safe measure, I would inspect the entire high side circuit just to insure you have no visible restrictions (crush hoses, bent or crushed ac fittings or condenser coil tubes).

O.K.- Used the compressor to pressure test the hi side-good pressure at the TEV.

http://forums.pelicanparts.com/uploa...1502490602.jpg
^^^^^
Vacuum values with an ongoing four hour pull, with manifold valves open.

I'll pull for another few hours, close the valves, and let sit overnight.

http://forums.pelicanparts.com/uploa...1502490569.jpg
^^^^^
Also replaced the TEV, and the Schrader valves on the pump.

We can discuss re-charge next week.

Have a nice weekend....

Best,

Gerry

The sensing bulb (copper pigtail attached to top of evaporator outlet pipe)

Your sensing bulb is incorrectly mounted. It should be mounted on the TOP of the evaporator outlet pipe and it should be covered in prestite insulation tape or an equivalent.

The sensing bulb should be measuring refrigerant gas outlet temperatures, this is why it is to be mounted on the top of the pipe.


The prestite insulation on the top of your TEV serves no purpose.

If your low gauge needle is pegged below 30" against the pin stop, like -32" ? that is well below a perfect vacuum, hence I'd test with your analog gauge against a digital gauge or verify vacuum with a micron gauge.

TEV's on 911's and 930's seldom fail on their own. The most common "failure" is not the components in the valve or their function.
Rather the failures are blockage in the valve due to debris or ice inside; either of which can cause the valve to appear to be failing
in a closed, partially open, or fully open state. The most common error in faulting a valve is when it is replaced and a better vacuum is achieved,
hence was it the valve or the procedure.

Here is mine:

http://forums.pelicanparts.com/uploa...1502498088.JPG

I do not have that fancy clip on mine