Stumped - incessant cycling and pressures all out of whack (

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Re: Stumped - incessant cycling and pressures all out of wha

Postby cornbinder89 » Tue Mar 07, 2017 4:12 am

OK, this is the part I have trouble with: How can the high side pull down lower than static pressure? Answer, there MUST be something restricting flow ahead of the port, What the gauges say to me, is the TX and evaporator have less of a restriction than whatever is restricting the line closer to the compressor. I can see no other way the high and low side readings can be equal (or damn near it). The problem I have, is if the low side is dipping from static pressure, than that refrigerant MUST be going somewhere.
Lets look at it another way. Lets say the compressor is FUBAR and is not compressing, if that is the case the low side would not drop, ergo the compressor is move some (may be not enough) refrigerant. If it is compressing even a little, we should see some increase of pressure on the high side over static pressure, but we are not. So the $10,000 question is what is happening to the refrigerant? Even if it is a variable displacement compressor and stuck in minimum displacement, it moves enough refrigerant to drop the low (and high) side gauges.
With a closed loop system like A/C, if you draw or move something from one side, it will eventually make it around the system to the other side. That doesn't appear to be happening (at least at the normal rate) here.
Some have found evaporators where they were assembled wrong, and instead of the baffles directing flow back and forth across the tubes, the baffles were put all in one tank and the refrigerant just entered one end of one tank and exited the other without going thru the tubes. I wonder if your condenser is doing something similar?
I come back to putting test taps between the compressor and condenser, between the condenser and Receiver/drier, and you already have taps after the drier, so were good there.
There must be somewhere after the compressor where the high side rises, if only a little (or may be a lot). The only other thing I can think of is the compressor is FUBAR and nothing that gets compressed makes it outside the compressor. In that case the crankcase of the compressor becomes a pressure chamber and once it becomes pressurized above low side pressure, no more refrigerant flows from the low side and the pressure stops dropping. The problem I have with that, is you would expect the compressor and or the belt to complain loudly!
Tom's suggestion of holding your thumb over the intake and outlet while someone turns the crank should show if the compressor is doing anything.
There may be compatibility issues with the mixing of components, but as you point out, it should do something, you should be seeing a rise in pressure, even if it is not enough to cool well.
SO, I come back to the same old, same old. Put taps in and take some readings. If you don't get pressure between the compressor and condenser, add a little more refrigerant, little a time to see if may be you don't have enough to shift the variable displacement into high?
Until the high side is over the low, nothing else matters nor can any other problem be diagnosed.
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Re: Stumped - incessant cycling and pressures all out of wha

Postby cornbinder89 » Tue Mar 07, 2017 4:51 am

Oh, and I wouldn't run it with the compressor on all the time. If refrigerant isn't moving neither is the oil. My guess is the reason it cycles when hooked to the PCM is the PCM detects a problem and is trying to save the compressor from damage.
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Re: Stumped - incessant cycling and pressures all out of wha

Postby Tom Greenleaf » Tue Mar 07, 2017 8:42 am

About now it's getting near certain that compressor has to be at least the source issue. Sorry for the waste of 134a just checked current price dropped for a 30 Lb. bottle to about $200 +/-. So you aren't recovering it and if so don't know if you get out what you know was put in.

Back to square 1. It may just pour out under pressure yet hold a vacuum as said first reply. That sure would cause all erratic problems worst is burning out compressor for lack of oiling not moving at the pressures posted.

What I don't get is how you get both pressures below what ambient temps would have it just sitting there when compressor is supposedly compressing? Where did the static pressure go with it running?

I feel your pain and now very worried there's just erratic debris and or bypassing items even compressor itself if variable is must be able to but still can't explain lower pressures somewhere when this compressor is running. Bit lost with this,

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Re: Stumped - incessant cycling and pressures all out of wha

Postby james92se » Tue Mar 07, 2017 9:56 pm

Sooooooo we found the problem! BTW yes there are two of us in this thread - James and Jonathan. We're brothers.

Anyway, we had a local (very well known) AC shop fab up this fitting for us to attach the GM pressure sensor:

Image

Jonathan took this entire line/hose off and compressed air would NOT blow through it. He cut the T fitting apart and it is TOTALLY BLOCKED OFF:

Image

Unreal. :x
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Re: Stumped - incessant cycling and pressures all out of wha

Postby Tom Greenleaf » Tue Mar 07, 2017 10:45 pm

Thanks so much for posting that - great for archives if nothing else. Sure had me going.

Perhaps chalk that dang part up to just plain poor quality control of them?

Good luck that compressor survived that stupid thing and be on to the next thing,

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Re: Stumped - incessant cycling and pressures all out of wha

Postby cornbinder89 » Wed Mar 08, 2017 12:20 am

Glad you got it. Sometimes, when it is out of the ordinary, you just have to break the system into short segments and check each segment. At least I have too.
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Re: Stumped - incessant cycling and pressures all out of wha

Postby jonathan_ed3 » Wed Mar 08, 2017 12:34 am

Idiotically, I never checked this portion of the line because it was 100% brand new AND it was showing pressure.

Of course had I checked this particular line from DAY ONE I wouldn't have taken this thing apart 3 times.

Taking it apart invokves draining all the coolant and the thermostat housing just to get to the compressor so it's been quite a PITA

Of course hindsight now reveals that what was happening was the discharge fitting at the evaporator/expansion valve was equalizing through the evap with the suction hose.

That's why the pressures were working in unison.

I've ordered all new parts including drier, codenser and compressor.

Since the blockage was before the expansion valve that protected my evap and expansion valve from the compressor pushing through any debris (if there was any to push)

By the weekend I hope to have COLD AIR!!
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Re: Stumped - incessant cycling and pressures all out of wha

Postby cornbinder89 » Wed Mar 08, 2017 12:45 am

Easy mistake to make. If it is new and simple, it doesn't seam like it would likely be the problem. I did and annual insp on a piece of equipment several years old, and it had a blocked fitting like you had, No one caught it because the machine worked normally in use. It was part of a "dump" feature to stop the machine from moving or doing anything in an emergency, when the E stop was tripped. I caught it, but took a long time to find the offending fitting even after I knew there was a problem.
I guess what I am saying, is for several years experienced inspectors missed it, so don't beat yourself up for not suspecting that fitting. It could happen to the best of us.
That's why I break the system down to manageable size sections that I can look over very carefully.
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Re: Stumped - incessant cycling and pressures all out of wha

Postby cornbinder89 » Wed Mar 08, 2017 3:08 am

If your switch port is 10mm male, there was a thread on where to find them here:
viewtopic.php?f=1&t=13483
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Re: Stumped - incessant cycling and pressures all out of wha

Postby jonathan_ed3 » Wed Mar 08, 2017 4:06 am

Thanks for the link. I'll remember that.

Yes it is 10mm, but it's 1.25 pitch. I've read that 3/8-24 is close enough that it works, but I already have the 10x1.25 valve that was custom made in a specialty run a few years back on ls1tech.com. I'm going to have a different AC shop cut it off my existing fubard fitting and braze or weld it into a #6 reduced barrier headlock splice. Then I can remake my hose and hopefully I'll be good.
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Re: Stumped - incessant cycling and pressures all out of wha

Postby cornbinder89 » Wed Mar 08, 2017 7:24 pm

You can buy the fitting already made, just for future reference. I don't know about reduced dia hose, but in conventional Beadlock I know it is made, 'cause I looked up for the guy in that other thread.
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Re: Stumped - incessant cycling and pressures all out of wha

Postby jonathan_ed3 » Thu Mar 16, 2017 3:23 am

So we got the system back together with the new pressure sensor fitting, oiled up and charged.

Again, have no clue how much to fill with so we went to the low end of the original Honda capacity (22oz).

And we got cold air out of the vents!

It was about 70 in the garage tonight, vent temp got right down to 40 and cycled off. At this point I don't if it was the Honda evap temp sensor shutting it down or the GM pressure sensor in the high side line. Vent temp creeped up to about 48-50, then clutch cycled back in. Repeat indefinitely.

Suction line was cold but discharge line wasn't hot at any point in the system.

Here's a video of the pressure gauges..

https://youtu.be/t3Jde7I1UrI

Thoughts? High side pressure seems too low. It'll be in the low 80's on Sunday so I'm anxious to see how it performs and what pressures look like. I realize the cooler temps like tonight aren't ideal for diagnostics, but gotta do it when i have the free time.

Of possible important note, the way the car is wired currently, the ac condenser fans come on immediately when the ac clutch engages or when the radiator fans come on. This is a limitation of the fans I'm using and the way the system is wired (wanted to keep it simple initially). Multi speed fans are used In the original Chevy configuration (lots of wiring and relays).

This may or may not be an issue with long term ac performance. Later on I may try to replicate a Chevy style three speed fan setup instead of single speed setup.
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Re: Stumped - incessant cycling and pressures all out of wha

Postby cornbinder89 » Thu Mar 16, 2017 4:02 am

High side pressure is a function of refrigerant temp. That being said, it does look a tad low. It is showing 85-90 deg condensing temp for the refrigerant. Either you have a really good condenser and good air flow across it, and cool air, such that the outlet temp of the refrigerant leaving the condenser is in the 85-90 deg range, or it is low and the outlet is all vapor. A temp reading of the outlet tube will tell. Also if the original R/D has a sight glass, you can get an indication visually. You should see mostly liquid with some bubble or foam.
at least the high side is riseing when the compressor kicks in! That is a good sign, and one you didn't have before.
If you can wait until you have a hot day so you can put a real heat load on the system, it will be easyer to gauge if you have enough. My guess is you are a little light on refrigerant. If you choose to add some, do it slowly a little at a time and allow the system to stabilize before adding more. Take notes and monitor the outlet of the condenser as well as vent temp.
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Re: Stumped - incessant cycling and pressures all out of wha

Postby cornbinder89 » Thu Mar 16, 2017 4:20 am

Re read you post, if it is in the mid 70's AT THE CONDENSER, than 85-90 deg outlet temp of the condenser is in the ball park, 10 to 15 deg over the air passing thru it.
Ideally you would want to shed ALL the heat but that isn't possible, the delta T (change in temp) goes down as the two fluids come close in temp, or to put it another way, if the temps are the same no heat transfer will take place, so the refrigerant HAS to leave the condenser warmer than the air passing thru the condenser. The closer those temps become, the better.
With a 70 deg day the heat load is light so it isn't a good test. With higher heat and outside temps, you still want the outlet of the condenser to be as close to 10-15 deg higher than the air temp.
Many expect to see high side pressures in the 175- 200 psi range, but that is only true when the condensing temp is high enough to see that pressure.
Pressure is a good indicator of refrigerant temp at the point of measuring, and little else. It is a common mistake to think it will tell you the amount (correct or otherwise) but it really only tells you the temp. You can infer how well the system is working by the temp, but not if the charge is correct or not. It is the problem I have wrestled with when I made my own systems, and one you will wrestle with when you combine two different systems.
AN ideal system will have all the refrigerant boil to vapor just at the end of the last tube in the evaporator, condense to all liquid in the end of the last tube in the condenser, with the vent temp being just above freezing and the condenser outlet temp being just over ambient temp. That is hard to achieve esp with changing temps and heat loads.
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Re: Stumped - incessant cycling and pressures all out of wha

Postby jonathan_ed3 » Mon Mar 20, 2017 1:23 am

It was sunny and 82 today so we played with the ac some. Parked the car in the sun and let it idle.

https://youtu.be/bwkUy609RUU

We measured the lines at the inlet and outlet of condenser with a laser thermometer. Inlet at the condenser from the compressor was 109*, exit from the condenser to the drier was 120*, center vent outlet temp was 45*
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Re: Stumped - incessant cycling and pressures all out of wha

Postby cornbinder89 » Mon Mar 20, 2017 2:10 am

Forget your laser thermometer, it is showing you are gaining heat at the condenser! Your high side pressure is showing a condensing temp of 135-140 deg, which is a bit high. Grab the outlet of the condenser with your hand, if it is hot then you are not shedding enough heat. The outlet of the condenser must always be cooler than the inlet.
If you have too much 134a in the system, liquid will back up in the condenser and you'll loose capacity so the high side pressure will increase. The condensers job is to remove heat from the vapor so it will condense to a liquid. When that happens it takes up much less volume so you don't need high pressure. If the condenser is big enough and the right amount of refrigerant is in the system, you would expect to see condensing pressure (temp) of about 10 degs hotter than the air passing thru the condenser, so at 82 deg I would expect high side in the 92-100 deg range or pressure of 115 to 120 psi.
So, you may have too much refrigerant or you need a bigger condenser or better air flow thru the one you have now.
If I had to hazard a guess, I would remove a little 134a and see what the pressures do.
With the correct amount and a big enough condenser, the outlet should be warm, warmer then the air but not hot. The inlet can be hot, but you should a large drop in temp across the condenser.
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Re: Stumped - incessant cycling and pressures all out of wha

Postby jonathan_ed3 » Mon Mar 20, 2017 3:53 am

Thanks for the reply.

Thankfully I'm off this week so I have free time to play with it.

The condenser is as big as will fit in the car.

I have another fan I can turn on. I dont have it hooked up yet. In the video and for the temp tests there was only one dedicated condenser fan running.

The exit line between the condenser and drier is definitely very warm. I wouldn't call it hot but I think the temp shown on the laser thermometer is pretty accurate. It's hard to get my hand into a location near the condenser inlet for a hand test but I'll try tomorrow.

I can also throw some running water over the condenser to achieve additional cooling. If I do so, and the exit line from the condenser still doesn't show a large drop in temp across it, should I think about reducing the amount of refrigerant in the system?
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