Txv

[86 911 Targa]

With the exception of debris in the system,
is it possible for the TXV valve to fail in
a "closed" mode?

I have what appears to be a blockage
"somewhere" in the system as the
low side pressure drops to nearly
0 @ 2000 rpm's.

The high side is @ 175 psi.

Center duct temp is 60f on a 75f ambient.

Thanks in advance,

Gerry

[T77911S]

I had a desiccant ball come lose and block my TXV on my truck, but we have a receiver/dryer which is after the TXV. suppose one could clog the comp.

closed if the gas leaks out of the bulb.

[76FJ55]

The receiver drier is actually before the tv, so I guess it is possible that the desicant could have clogged the tv but don't know that that would be my first assumption.

Can you provide any more details on your system?
History of A.C. functionality.
When did the problem first occur?
R12 or r134a?
Last time it was serviced?
Stock or modified system?
...

[86 911 Targa]

^^^^^
The system is stock, with the exception of a pro-cooler,
and worked very well prior to this event.

Using R-134.

Here is what took place.

During a smog check @ 2K rpm's the low side connector
came off.

We promptly shut down the car.

Perhaps "something" was injected into the rear condensed.

Thanks,

Gerry

[76FJ55]

That is actually the high side connection.
How much freon was put in. At first glance with your high side pressure andR134a, I'm inclined to think you are under charged

[86 911 Targa]

I charged about 18 oz, of R-134.

At idle, I have about 30 low, 125 high.

When I increase the rpm's to 2K the low side
drops down to zero.

I replaced the entire system, and
transitioned to R-134 from R-12 about a year ago,
all worked very well, and
had excellent cooling until this event.

[86 911 Targa]

^^^^^
Existing TXV pic.


^^^^^
New TXV pic.

Not sure if that is debris, or typical.

Could it be preventing the TXV from opening all the way?

I have a small compressor,
and will try to blow out all of the refrigerant
hoses individually.

A bit of work, but it might uncover a blockage location
if one exists.

Thanks in advance to all.

Best,

Gerry

[76FJ55]

18 oz seems light. I added a 3rd condenser in the rear wheelwell so mine is different than yours, but I think I'm near 36 oz, with 32 deg. vent temp on triple digit days.

[76FJ55]

So when the line blew off, was the car running with the engine bay open? If so I'd guess you over pressured the high side causing that line to blow off. R134a should really have a binary switch to shut off the compressor in the event of either low pressure (lack of significant freon to carry oil) or excess high pressure (damage to high pressure circuit)

[86 911 Targa]

Originally Posted by 76FJ55

So when the line blew off, was the car running with the engine bay open? If so I'd guess you over pressured the high side causing that line to blow off. R134a should really have a binary switch to shut off the compressor in the event of either low pressure (lack of significant freon to carry oil) or excess high pressure (damage to high pressure circuit)

Note: Deck lid was open for smog test.

I suspect that the hose was not properly crimped
when I installed the new system.

What are your thoughts on the two pics of the TXV?

My concern at this time is the blockage.

[76FJ55]

The area you have pictured is the outlet side of the txv, so I would be surprised if what you see would cause any kind of issue with the valve. My first guess is that it is oil residue. you could confirm this by taking something soft, like a cotton swab and see if you can wipe it clean and then what it looks like on the swab (under magnification if you have it).

That Line may not have been crimped correctly, or the other possibility is that the high side over pressured, and that was the weak link. With the engine bay open, the condenser will loose cooling are flow, which is driven by the airflow generated by the engine cooling fan. As the system is still pulling heat in at the evaporator, and the compressor is also generating heat, the high side pressures can effectively run away since there condenser cooling.

When you did your R134a conversion did you intigrate a low pressure or binary cutoff switch?

[76FJ55]

Just noticed the square in the last picture. there is a cutoff switch installed. Is it a binary switch? how is it wired in?

[86 911 Targa]

Originally Posted by 76FJ55

Just noticed the square in the last picture. there is a cutoff switch installed. Is it a binary switch? how is it wired in?

It is a high/lo switch which is connected to the high side of the compressor,
and the 12v.

[76FJ55]

That all sounds good. I'm still inclined to think 18 oz just isn't enough freon.

When you got the 175 psi high side pressure was that with the engine bay open or closed?

[86 911 Targa]

Originally Posted by 76FJ55

That all sounds good. I'm still inclined to think 18 oz just isn't enough freon.

When you got the 175 psi high side pressure was that with the engine bay open or closed?

Closed.

[proporsche]

Hi boys..just to add to this with 134
low press...Blue 18-34
high press red 150-220

ivan

[T77911S]

if you had a clog/TXV fail, that would have over pressurized the hi side and that could be why the hose blew off.
most systems have a low pressure switch, some also have hi pressure switch to prevent just such a thing from happening.


best thing to do is get some AC flush and flush all hoses and all coils.
replace dryer and TXV valve. hope the comp is still good.

[76FJ55]

His system has a high pressure cut off so the over pressurization should be less likely. For the initial failure, I am leaning toworards his original suggestion of the hose assembly being weak from manufacture.

I'm still of the opinion that his current problem is under fill of freon. If it were me I'd try adding another 4 oz or so and see what that does for vent temps. He's still got plenty room on the high side, and vent temps and low side both indicate he isn't filling the evaporator sufficiently for adequate cooling.

[86 911 Targa]

Originally Posted by 76FJ55

His system has a high pressure cut off so the over pressurization should be less likely. For the initial failure, I am leaning toworards his original suggestion of the hose assembly being weak from manufacture.

I'm still of the opinion that his current problem is under fill of freon. If it were me I'd try adding another 4 oz or so and see what that does for vent temps. He's still got plenty room on the high side, and vent temps and low side both indicate he isn't filling the evaporator sufficiently for adequate cooling.

Good morning all,

I replaced the TXV valve and,

pulled a good vacuum which held overnight.

Recharged the system with 22oz of r-134.

With 175X30 pressures at idle, I get no cooling at the ducts.

At 1800rpm's I have 250X10 pressures-very if any cooling at the ducts.

I'm thinking that when the high side hose blew, debris entered the system.

Pressure tested both front and rear condensers, and evaporator-no debris.

I'll re-check the new TXV valve for debris.

Currently pressure testing the other hoses one at a time.

Thanks,

Gerry

[Bob Kontak]

Originally Posted by 86 911 Targa

I'll re-check the new TXV valve for debris.

Roughly on topic...........

I just performed some AC work on a 90 Volvo dump truck changed to R-134 with a pretty big Sanden. One hose dry rotted with leaks so has been open to atmosphere long time.

Had hose built. Held vacuum and charged for fun. High side parts got warm. Low side parts no change. No cooling. First thought txv.

Pulled off the rectangular cube-like txv and it's full of micro-bb's in one of the four ports. (everything runs in and out of this block)

Called Charlie, he said the bag/ball ripped in the dryer but there is a chance only the line from the dryer to the txv is contaminated given the orifice is so small. Pulled hose and it was packed with little balls at the evap end.

Purged it, new dryer/tvx/vacuum.

Reason I am posting is the system "works" but the pressures are similar in performance. Low drops over time (down to maybe 10)and high has not hit 200 psi yet.

I think the prudent thing to do is the big clean with fresh oil added. I don't want to hit the customer with the need for a compressor if the system is filled with cooties from sitting "open"

However......................some older F-250's take 3 lbs of refrigerant. This is a 20,000 lb truck. I only put in 2lbs because I don't know the capacity.

I may be undercharged?

In short, subscribed.