Low side low, high side high! Help!

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Crewcabdart
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Low side low, high side high! Help!

Post by Crewcabdart »

Hello all! I’m working on my 1972 Plymouth Valiants “universal” hodgepodge ac system and I can’t get it right!

I’m using the engine/ compressor from a 1996 Dodge Dakota, a universal 16x26 Parallel flow condenser (CNFP1626), I custom made all my lines, a universal drier, a universal expansion valve (old school style, but without the oil line that screws into the suction side) and I’m using the factory evaporator core.

At first I believe I was fighting inadequate condenser airflow, so I added two 10” fans temporarily to see if that helped. It did help, but high side pressures would still peak around 450 psi with the low side only seeing around 30!

If I secure the expansion valves thermostatic coil to the suction side it will blow cold (50 degrees or so with ambient temps around 85), but it brings the low side down to 26 and will immediately cycle the clutch rapidly off idle. (High side hanging north of 400 at this point)

I can test the TXV with my hand and cold water and can watch the pressures change, so it’s not stuck.

I also pulled a vacuum for over 2 hours, but the drier had been cracked open a day prior (resealed maybe 20 minutes after) to charging. I’m not ruling out a saturated drier, but the sight glass is clear as can be.

All components and lines are brand new. The compressor manifold and evaporator core were flushed multiple times before installation. I’m really scratching my head here.
tbirdtbird
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Re: Low side low, high side high! Help!

Post by tbirdtbird »

"The compressor manifold and evaporator core were flushed multiple times before installation. "

What flush was used? How was it removed?
We had a guy that wanted to flush his lines with soap and water.
Doubt your drier is saturated.
Condenser sounds small. You want the biggest condenser you can get to fit.
You could also be overcharged if the sight glass is clear. Correct amount of 134 will not clear a sight glass, assuming you are using 134.... How did you determine how much 134 to install?
What state (ie what is your highest ambient)
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Tim
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Re: Low side low, high side high! Help!

Post by Tim »

I'd double-check the plumbing, Discharge on top, and liquid to the in-side of the drier. How much refrigerant was added, as mentioned? Attach the probe, it is needed!
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Crewcabdart
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Re: Low side low, high side high! Help!

Post by Crewcabdart »

I used AC flush from the parts store. Unsure on exact amount of Freon as it came from a 30lb bottle. I played with amount and it never made a difference really. The high side would come down, but the low side would still hang around 26 and cycle immediately.

This condenser is the biggest I can fit for my situation, and many other guys on the same vehicle and system have used it with great luck.

Yes R134A.

And if you mean by “what state” I’m here in Mississippi. It gets hot haha.

My plumbing is as follows:

#8 line from high side manifold to top of condenser, #6 line from bottom of condenser, through drier, to top of TXV. Factory liquid line from bottom of TXV into condenser. #12 to #10 adapter coming out of the evaporator core back to the #10 suction port on the manifold.
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Tim
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Re: Low side low, high side high! Help!

Post by Tim »

Make sure your drier direction is correct.
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Crewcabdart
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Re: Low side low, high side high! Help!

Post by Crewcabdart »

Inlet is screwed into the side labeled “IN” on the drier.
tbirdtbird
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Re: Low side low, high side high! Help!

Post by tbirdtbird »

I am still thinking overcharged; improper condenser airflow. Improper TXV since temp drops so much (over feeding).
Parts store flush is nothing to write home about, it leaves a nasty residue.
Hold the input and output at the evap with each hand and compare...should be about the same temp.
With condenser fans running, and with engine at 1500 RPM, max fan, max cool, recirc, you need to charge to a hi of about 225 in an ambient of about 85. Do this by installing a tiny amount of 134 at a time and allowing the system to stabilize before adding more.

Did a comp ever grenade on this system? Why are you replacing the comp
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Crewcabdart
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Re: Low side low, high side high! Help!

Post by Crewcabdart »

tbirdtbird wrote: Fri Jun 02, 2023 2:34 pm I am still thinking overcharged; improper condenser airflow. Improper TXV since temp drops so much (over feeding).
Parts store flush is nothing to write home about, it leaves a nasty residue.
Hold the input and output at the evap with each hand and compare...should be about the same temp.
With condenser fans running, and with engine at 1500 RPM, max fan, max cool, recirc, you need to charge to a hi of about 225 in an ambient of about 85. Do this by installing a tiny amount of 134 at a time and allowing the system to stabilize before adding more.

Did a comp ever grenade on this system? Why are you replacing the comp
I will make a fan shroud for the clutch fan to see if I can get some more condenser airflow. Input and output of the evaporator core are relatively the same temperature. Both cold sweating. With the sensing bulb fully secured to the evaporator outlet the system will blow cold (50 degrees at idle on a 85 degree day).

I will try putting some in little by little.

New compressor because this is an all new made from scratch system. My engine didn’t come with one.
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Tim
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Re: Low side low, high side high! Help!

Post by Tim »

[/quote]

I will make a fan shroud for the clutch fan to see if I can get some more condenser airflow.
[/quote]

That will make a huge difference.
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tbirdtbird
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Re: Low side low, high side high! Help!

Post by tbirdtbird »

"I will try putting some in little by little."
YIKES!!! NO!!!!

I meant when you are charging from empty, since it doesn't seem like you knew the correct charge

If you add any more now your hi side will go even higher

As Tim said, fan shroud will help a lot. If a clutched fan, how old? The viscous coupling wears out (thins out) and will not drive the fan at the correct speed. If new, you are OK. But we have posters here whose only problem is a bad fan clutch.
With a bad clutch, the engine will NOT overheat but the AC WILL suffer
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