A/C - low side & high side pressures?

[dw1]

The car is a mostly stock '87 coupe black/black so even with tinted windows, a/c having at least some functionality is a must.

It was converted to R134a before I bought the car some years ago, but nothing else was changed. Last year I replaced all of the hoses and rebuilt the compressor (kudos to Griffiths, btw) and it was working fairly well...for a while.

Now that the weather is getting warmer here in the northeastern US, I checked the a/c today and found the vent temps were not all that much different from the outside air temperature.

More importantly, the pressure measurements on a 65-70°F day at approximately 2500 rpm were 15 psi low side and 225 psi high side.

Oh, and last year I had the evacuation & recharge done at a local Porsche shop and I think they over-charged it. A lot.

So I'm thinking that replacement of the hoses and flushing out the condensers & evaporator loosened up some crud that eventually found its way to the expansion valve. Is that the most likely problem, or is there something else I should be looking at?

Also, our sponsor has a wide spread in the prices for compatible expansion valves - wtf?

[GH85Carrera]

The factory stock AC system in perfect working order, on a HOT day is about useless. It is great for night time or cooler weather. When you replaced the hoses, did you pull out the evaporator and look at it?



This was my original evaporator. Changing it helped a lot, but the only real cure was two more condensers from Griffiths, in the rear fender.

Just this Saturday we were on a road trip back to home. In Arkansas it was 100 degrees in the afternoon sun with the sun shining right on our bodies. The dash was too hot to touch. Griffith's 4 condenser system was cranked to MAX, and we were not not sweating. I think my system might be low on refrigerant. I made a similar trip two years ago and I got cold and had to dial back the AC. I have not checked the pressures in several years.



In temps of 90 or so the return pipe back to the compressor will frost up, keeping the compressor cool.

Hopefully Charlie will chine on on the thread.

[wazzz]

Glen, are you still on R12? Just asking because I don't see any R134a red and blue ports on your pic.
My return line is also sweating and very cold, but not frozen. That could be dangerous for compressor if ice cubes are sucked in. -

[GH85Carrera]

Yes, Still using R-12. I bought a 30 pound bottle of it back in the 80s for $45. I recover any in the system before I work on the system.

My 1986 El Camino also returns cold liquid to the Accumulator.



It uses a Accumulator and orifice tube system and was blowing 38 degree air yesterday in 95 degree heat with a heat index of 110. And it blows a lot more air than the 911, even with the Hurricane blower from Griffiths on my 911. You can see the bottom line is where the orifice tube turns the liquid to gas.

The gas returning to the compressor is a gas, no liquid, only the compressor can compress the gas back into liquid form. Keeping the compressor cool always is good.

[Discseven]

From what you've said Dw1, I like a leak here. Reason: a clog at the TXV would likely (not guaranteed) be an abrupt change in performance. A progressive performance decline is the signature of a leak. With all the connections that MUST be and remain perfect, it calls for surgical precision to get EVERY connection just right. And even if this gets done, hardware can fail...



Above is best AC performance I've managed to find---the outcome of an AC science experiment lasting 10+ years. Lots of trial. Lots of errors. System is NOT stock. Refrig is R134. Charge weight: 23 oz. Readings at: 2000 rpm. (Record shared here was taken while cabin was in progress of cooling off. Vent of 23 dF and evap of 31.2 dF seems odd. Is due to the hysteresis set to freeze the evap* slightly but not allow it to turn into a block of ice. A delicate balancing act to be sure.) Here's the point, having arrived at more cold than is actually comfortable, I thought I was finally DONE with the quest for a cold AC. Nope. System "very slowly" went to chit. Small leak? Yes. Real small. Was NEW pressure switch that leaked out where the electrical wires go in/out of unit. (Leaker is UAC brand made in China. Cost: $17. PS with spade electrical connections might be a better choice---going with that format next.)

You may be right about crud in the TXV. If I may however, before dealing with that, I suggest having a methodical look at everywhere where the system could possibly leak out. That is if you are DIY inclined on this. Leaking area(s) is often wet/moist. With static pressure still in the system, the leak may even gurgle---super tiny gurgle possibly but gurgle none the less. My pressure switch did this. Was also wet. With 40 feet of AC hose, I look at the major connections first. Takes a few minutes. If nothing is found, then it's a matter of inspecting every inch. Not a simple task but I shall propose it being a very meaningful endeavor. If a leak---there can be more than one---is not found, then all the time, effort, materials that go into charging are wasted.

Bottom line, my advise is to spend time looking at the system before spending money on it.

* Evaporator: Kuehl serpentine

.

[GH85Carrera]

One of the things I do before every recharge, is my belt, suspenders, with glue double extra overkill vacuum and charge procedure.

I start off with a two hour vacuum, with my micron gauge attached. I let that sit overnight, and if there is a rise in pressure. Then I purge with nitrogen to 100 PSI or so, and go looking for leaks at every connection I can get to with a small paint brush and soapy water. I then pull two hour vacuum, and purge again with nitrogen to be double sure there is no hidden moisture hiding as ice in the vacuum. Then I change the oil in my dual stage vacuum pump, and pull a 4 hour vacuum, then finally charge with refrigerant.

I am positive after that there is zero moisture in the system, and there are no leaks. I usually go for years before I even need to check the charge. I would have to look at my records to find out how many years it has been.

My system is all Griffiths, except the front and rear condensers, which are the ones that came with the car. I have his variable speed fan control, and hurricane blower. Both are well wort the cost and effort to install them. The two condensers in the rear fender is the real answer to more cold air. I have his evaporator, hoses, receiver-dryer, and the added vents since my car is an 85 with the tiny vents on the side of the dash.

All the plumbing and such was done in 2007. It is all working great.

[dw1]

Thanks to everyone for your inputs.

GH85Carrera - that is one impressively cruddy evaporator. I hope you had an up-to-date Tetanus shot.

Btw, while my evaporator is OEM, I saw that it was surprisingly clean when I changed all my hoses to barrier-type (and changed the filter-drier) last year. Very good suggestion to check it out, tho.

I did get a new expansion valve from Charlie Griffiths (and talking to him always teaches me a few things) and I think between that and my own investigations I have the issue sussed.

Before installing the new valve, I went over the system carefully looking for leaks but found none. I tightened a few things "just in case".

I vacuumed down the system to 30 inch Hg vac. as measured by my analog gauge, and while it held in the 29-30 range after sitting closed for 30 minutes, after 12 hours it was up to 20 inch Hg vacuum. I then vacuumed down the system a second time and interestingly this time the vacuum held at 29-30 in Hg for more than 24 hours.

After installing the new expansion valve (because - what the heck, it can't hurt) the vacuum is holding at the minimum reading of my gauge (< 30 in Hg vac, depending on local atmospheric pressure - yes, I know 29.92 is the textbook nominal "zero").

So maybe just not a great vacuum & "clean" recharge last year? Or an extremely small leak at (or even in) the old expansion valve?

I did have the recharge performed last year at a local independent Porsche shop who got done with it surprisingly quickly.

This time, I'm taking as long as it takes to do it myself

[Nick Triesch]

When In replaced my expansion valve it ended my high pressure ac numbers and then the system worked correctly.

[dw1]

Just to let anyone following this thread know the results after the expansion valve replacement, one more evacuation, and charging with approximately 40 oz of R134a (I don't know exactly how much was lost in venting the input hose with each 12oz can)

On today's 90°F day with bright sun (NY/NJ area) but reasonable humidity (55% r.h.) I could drive my black/black car comfortably with the a/c and fan on high. Vent temps 48 to 54°F.

Not bad for an otherwise stock system. I'm happy. For now.

[GH85Carrera]

Originally Posted by dw1

Thanks to everyone for your inputs.

GH85Carrera - that is one impressively cruddy evaporator. I hope you had an up-to-date Tetanus shot.

Btw, while my evaporator is OEM, I saw that it was surprisingly clean when I changed all my hoses to barrier-type (and changed the filter-drier) last year. Very good suggestion to check it out, tho.

I did get a new expansion valve from Charlie Griffiths (and talking to him always teaches me a few things) and I think between that and my own investigations I have the issue sussed.

Before installing the new valve, I went over the system carefully looking for leaks but found none. I tightened a few things "just in case".

I vacuumed down the system to 30 inch Hg vac. as measured by my analog gauge, and while it held in the 29-30 range after sitting closed for 30 minutes, after 12 hours it was up to 20 inch Hg vacuum. I then vacuumed down the system a second time and interestingly this time the vacuum held at 29-30 in Hg for more than 24 hours.

After installing the new expansion valve (because - what the heck, it can't hurt) the vacuum is holding at the minimum reading of my gauge (< 30 in Hg vac, depending on local atmospheric pressure - yes, I know 29.92 is the textbook nominal "zero").

So maybe just not a great vacuum & "clean" recharge last year? Or an extremely small leak at (or even in) the old expansion valve?

I did have the recharge performed last year at a local independent Porsche shop who got done with it surprisingly quickly.

This time, I'm taking as long as it takes to do it myself

That is not uncommon. I suspect (no direct evidence) that as the vacuum increases some water or moisture in the system freezes into ice. It takes a LONG time to sublimate that ice into vapor, and that raise the pressure. That is the reason I go all overboard to get all the ice and moisture out with a double nitrogen purge. It is impossible to have too good of a vacuum, the better the vacuum, the better the AC works. Moisture is bad pookie for AC.

[88911coupe]

Glen, when you use the micron gauge what micron count are you trying to get to? For some reason I'm thinking I read anything below 350 is sufficient? Also, when you recharged did you just vent the line to let the R134 purge the line or did you use a vacuum pump to evacuate the line? thanks, Buck

[GH85Carrera]

I get into the double digits for the micron level. I only stop when it will not go lower.

And no, I never just vent the refrigerant. I have a compressor to recover it into an storage tank. I use that tank to recharge my El Camino. I am prejudice, and only give my 911 fresh new refrigerant. The El Camino can reuse the old stuff. And I am still using R-12. I bought a 30 pound bottle from Sam's for 35 bucks long ago. I ONLY work on my two cars AC.

[T77911S]

500 for micron reading.
if i can get it below 1000 and it holds im ok with it.

[McLovin]

Originally Posted by dw1

Just to let anyone following this thread know the results after the expansion valve replacement, one more evacuation, and charging with approximately 40 oz of R134a (I don't know exactly how much was lost in venting the input hose with each 12oz can)

On today's 90°F day with bright sun (NY/NJ area) but reasonable humidity (55% r.h.) I could drive my black/black car comfortably with the a/c and fan on high. Vent temps 48 to 54°F.

Not bad for an otherwise stock system. I'm happy. For now.

That’s not bad temps for a 911. The 911 AC is hampered by non optimal condenser placement areas and condenser size. Almost all cars have a huge area in the nose where a large upright condenser can be placed directly in high speed cool airflow. Not so with the 911.