Need Help- High Pressure on Discharge Side

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69DropTop
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Re: Need Help- High Pressure on Discharge Side

Postby 69DropTop » Thu Jul 26, 2018 6:22 pm

Came home from work and messed around with the A/C for a while. I fired the car up, hooked up the gauges, turned on the A/C and after about a minute or so the high side got up to about 300 so I set the garden hose on mist and squirted it right at the inlet of the condenser, the high pressure instantly dropped, down to maybe 200 or so.

What is weird is that after I put the hose to it no matter what I did the high side never got higher than about 300 without water. I even had my girlfriend hold the gas to what I'm going to guess was around 2000 rpm and the pressure never got higher than 300 without water on the condenser. I did notice when she was holding the throttle that the high side gauge would rise and fall a little- see youtube video link below, not sure what's up with that. I also heard the discharge hose smack around a couple times as soon as the car started with the compressor on which it hasn't done since I did the first charge on the system and discovered the high pressure problem.

Anyone have any ideas what was up with the results I had tonight and what should be my next step?

https://youtu.be/g4YohlZPWLI
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bohica2xo
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Re: Need Help- High Pressure on Discharge Side

Postby bohica2xo » Fri Jul 27, 2018 8:03 am

In 45 years of working on stuff with hoses I have only seen a liner collapse twice. The second one was 2 months ago on my pool chlorinator. So it is possible. And yes, that could be intermittent. But it is not very common.

I did have an odd hose related thing on an OEM system once - a whistle. It only happened at shutdown and sounded like a cartoon falling bomb. The dealer had done an evac & charge with no change. So I recovered it & pulled the OT. Wedged in the tube area was a piece of hose liner that looked just like a tiny clarinet reed. And it would only oscillate once the system stopped and things began to equalize with gas passing through the OT.

The hunting you are seeing looks like the TXV. Is the sensing bulb firmly clamped to the evaporator in the OE location? Insulated from engine heat with the presstite tape?

Obviously something changed in your system. When a refrigeration hose liner fails, generally they begin to leak, and sometimes swell where the failure happened. This is a tough call in a system full of R12. Do you have a way to recover the system?
69DropTop
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Re: Need Help- High Pressure on Discharge Side

Postby 69DropTop » Fri Jul 27, 2018 9:42 am

Ok that is very good to hear I'm most likely not dealing with a collapsed liner. I have not seen any swelling or leaking in any of the hoses.

What is weird is I never saw that hunting before and now the high side doesn't go up as high as it did before which it would almost immediately shoot up to 400psi if I took it slightly off-idle.

The sensing bulb is clamped to the outlet of the evaporator, it is currently not insulated, but I planned on putting the proper insulation on it once I got the system up and running properly.

I'm wondering if I have something odd like you had where i have a partial restriction and maybe "shocking" the condenser last night with cold water caused it to move?

As far as evacuating the system I don't have any equipment, but it's not a full charge yet; the discharge air in the car was just beginning to cool down when i quit charging it. My brother has an '86 Jag he's working on for someone, I was planning on hooking my car up to it as to not waste the R12.
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bohica2xo
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Re: Need Help- High Pressure on Discharge Side

Postby bohica2xo » Fri Jul 27, 2018 10:17 am

Insulating the sensing bulb should fix that hunting.

I would say you are on the right track, the shock may have moved some trash. The hunting appeared once you had full refrigerant flow. Hopefully the trash wound up in the accumulator never to be heard from again.

We looked that ford over hard, and the best guess from looking at the rubber piece was that when the hose was assembled the fitting skived off the piece of liner when it was inserted. Just a freak thing. We replaced the hose it should have come from & sectioned the whole thing - but found no missing liner.
69DropTop
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Re: Need Help- High Pressure on Discharge Side

Postby 69DropTop » Fri Jul 27, 2018 11:58 am

That's good to hear insulating the bulb should fix the hunting issue. I was beginning to get scared that it was a sign of the compressor going out and that it didn't have enough left in it is why it wouldn't hit 400psi anymore. Since the pressure is still somewhat high do you think I should replace the condenser and re-charge it or top this charge off and see what happens; I'm not really sure how much more it needs, but it was started to get cool when I quit charging it.

Yeah, would be nice if the trash is gone and in the accumulator, but I'm not sure whatever the blockage is that it's all the way gone because the pressure is still a little high, but thinking outloud here, I think the pressure only got to 325 and that was with the car sitting still and holding the rpms around 2000.

Does sound like a freak thing you had, I guess a mis-manufactured hose? I wonder if what I'm experiencing is a freak thing also because there has been no dead give away and people have suggested it could be a few things.
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bohica2xo
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Re: Need Help- High Pressure on Discharge Side

Postby bohica2xo » Fri Jul 27, 2018 12:07 pm

An R12 system should have a sight glass. That is how they were charged when new.

325 psi @ 2000 engine is not a big deal, depending on ambient. I know I will see more than that today @ 115 ambient. As a reference look at the P/T relationship between the high side & ambient temperature. 2.5:1 is good 3.0:1 is acceptable 3.5:1 is not acceptable with automotive work.
69DropTop
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Re: Need Help- High Pressure on Discharge Side

Postby 69DropTop » Fri Jul 27, 2018 1:21 pm

Unfortunately some nimrod "custom" made hoses for it, at least I think they are a/c hoses because they say Four Seasons on them, and there is no more sight glass. :x

I think 325 was the highest I really saw it after putting the hose to the condenser and ambient temp was probably 82. Thanks for the ratios! I will have to keep them in mind and will probably write them on the lid of my a/c gauges box in sharpie so I don't forget. I'm guessing those ratios are for when the engine is at idle?

So do you think I should go ahead and finish charging to see what happens? Any recommendations on charging procedure since I don't have a sight glass and am charging from a bulk container? I was just going to reference the temp/pressure chart in my A/C manual and charge off pressures.

By the way, thanks for all the info, replies and help! :D
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bohica2xo
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Re: Need Help- High Pressure on Discharge Side

Postby bohica2xo » Fri Jul 27, 2018 4:41 pm

Well that was the Cougar with the odd receiver dryer, so it could well have had the inline sight glass Ford used. Or it may have been on the side of the TXV - look at the pics in this thread:

https://www.autoacforum.com/messageview.cfm?catid=4&threadid=16459
69DropTop
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Re: Need Help- High Pressure on Discharge Side

Postby 69DropTop » Fri Jul 27, 2018 8:43 pm

I will have to take a closer look at the TXV valve to see if there is a sight glass. I am pretty sure the factory setup has the sight glass right behind the outlet of the receiver drier and it was built into the line that connected to the receiver drier.

I messed around with it a little more tonight and thought I would add a little more charge and see what happened. In the process of adding more refrigerant I looked down and saw the high side went up to 400 PSI again. I took the garden hose to the condenser and was only able to get a drop of about 25 psi. I just happened to put my hand on the sensing bulb for the TXV and glanced over and saw the high side pressure drop. I did it a couple more times but didn't see much of a drop and I guess it's because my hand was getting cold from being on the bulb. I filled up a pot of hot water in the sink, dipped a rag into it, and held it over the sensing bulb. I watched the high pressure sink like a rock from 400 to about 250 psi. I did this a few different times with the same result. I am guessing the additional charge got the system colder and the problem is the sensing bulb on the TXV is not operating correctly.
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bohica2xo
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Re: Need Help- High Pressure on Discharge Side

Postby bohica2xo » Sat Jul 28, 2018 10:20 am

That is an unexpected response to say the least.

I was going to suggest that eventually whatever was blocking things may eventually find it's way to the TXV & cause you trouble eventually...

But since this is an R12 system & you have no way to recover it I would not have suggested a TXV R&R just for inspection. But clearly you are there now.

Sounds like you have a new TXV in hand, so at least you can get it closed back up in a timely manner. Look carefully in the line leading to the TXV with a good light, and inspect the old TXV for debris. Obviously if you find dessicant beads you have more to clean up, and the dryer may have failed - or the previous owner replaced a failed dryer & never checked things beyond it.

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