AC compressor question - Chevelle Tech
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post #1 of 18 (permalink) Old Aug 15th, 19, 7:57 PM Thread Starter
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AC compressor question

While idling the AC compressor relief valve relived pressure (AC was running and blowing cold). It's a Frankenstein system using a R4 compressor (pancake) and is running through a orifice system with cycle switch etc. (mostly stuff off a 95 Chevy truck if that helps any). I'm also using a Vintage air binary switch on the high side (30PSI low pressure cutoff 406 PSI high pressure cutoff). This system has been working for over a year btw. I'm assuming the compressor is tearing up and perhaps clogged the orifice tube? Main question is why did the relief valve open instead of the binary switch cutting it off before that happened?
Do I need a pressure switch on the low side? Also am I on the right track of trouble shooting here?

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post #2 of 18 (permalink) Old Aug 15th, 19, 8:08 PM
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Re: AC compressor question

Defective relief valve?
Overcharged?
Not enough air flow through condenser?

Wouldn't have anything to do with low pressure.

What Vehicle?
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post #3 of 18 (permalink) Old Aug 15th, 19, 8:35 PM
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Re: AC compressor question

Where is the binary switch located? Maybe it never saw the high pressure because of its location. A blockage before the binary switch would cause the hp relief to pop open.
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post #4 of 18 (permalink) Old Aug 15th, 19, 9:04 PM Thread Starter
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Re: AC compressor question

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Originally Posted by Dean View Post
Defective relief valve?
Overcharged?
Shouldn't be, never added Freon since I charged it the first time over a year ago, wasn't sure how much to put but I went by the standard temp/pressure chart

Not enough air flow through condenser?
Car was parked but condenser fan was running.

Wouldn't have anything to do with low pressure.

What Vehicle?
72 el camino, only thing stock in the AC system is the air handler in the cab

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post #5 of 18 (permalink) Old Aug 15th, 19, 9:09 PM Thread Starter
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Re: AC compressor question

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Originally Posted by DUTCH MAX HEADWORK View Post
Where is the binary switch located? Maybe it never saw the high pressure because of its location. A blockage before the binary switch would cause the hp relief to pop open.
Binary switch is on a hose about 10 inches from the evaporator core on the hose that connects it to the condenser.
Also I pulled the orifice tube it wasn't clogged but they did have some threads of metal shavings and some black crud in it, guessing black stuff is from the dryer?

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post #6 of 18 (permalink) Old Aug 15th, 19, 10:22 PM
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Re: AC compressor question

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Originally Posted by sampoerna415 View Post
Binary switch is on a hose about 10 inches from the evaporator core on the hose that connects it to the condenser.
Also I pulled the orifice tube it wasn't clogged but they did have some threads of metal shavings and some black crud in it, guessing black stuff is from the dryer?
Anywhere from the compressor to the switch could be a blockage that would keep the switch from detecting the high pressure. A defective high pressure switch is possible.

Black metal flake in the orifice tube is not a good sign. How does the compressor feel when you spin the input shaft by hand? Possibly the compressor. Remove the compressor, drain the oil and catch it so you can measure how much came out. Was your compressor making any strange noises lately?

You said a drier but most orifice tube systems have an accumulator mounted after the evap and before the return/low pressure hose to the compressor. A drier is located between the condenser and the evap. Where's your located? Got a picture? My answers are a little vague because I'm not familiar with your Franken system. Some pictures of your system would be helpful.

2 Videos show what is in an accumulator or Receiver/drier. Both have screens in them to catch debris.
https://youtu.be/eOzA2FeJ_Fk
https://youtu.be/R8_j4nI_ThI

Last edited by DUTCH MAX HEADWORK; Aug 15th, 19 at 10:40 PM.
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post #7 of 18 (permalink) Old Aug 16th, 19, 8:23 AM Thread Starter
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Re: AC compressor question

Whoops, you are right Dutch I'm using an accumulator not a dryer I used the wrong word for that. There has been a bit of a squeak from either the compressor or belt tensioner, but it would go away after a few minutes. Now the compressor seems unusually easy to turn, there is a slight drag but I can turn it with one finger with a stub ratchet. Also the wiring for the compressor switch it run on it's own circuit (not using any of the factory stuff).
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post #8 of 18 (permalink) Old Aug 16th, 19, 9:23 AM Thread Starter
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Re: AC compressor question

Also 8oz. of PAG 150 was used in the system.

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post #9 of 18 (permalink) Old Aug 16th, 19, 7:23 PM Thread Starter
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Re: AC compressor question

Pretty sure I found the issue, I was checking the electrical system and the relay I'm using for the condenser stops working after about a minute, changed the relay and it's working correctly now. Still scratching my head as to why the binary switch didn't catch this. Maybe the setting is too high? The low pressure shut off is working on the switch. Perhaps 406 psi shut off on the switch is too high? Anyone know what the pressure relief valve is set to on a R4 compressor?

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post #10 of 18 (permalink) Old Aug 17th, 19, 12:22 AM
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Re: AC compressor question

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Originally Posted by sampoerna415 View Post
Whoops, you are right Dutch I'm using an accumulator not a dryer I used the wrong word for that. There has been a bit of a squeak from either the compressor or belt tensioner, but it would go away after a few minutes. Now the compressor seems unusually easy to turn, there is a slight drag but I can turn it with one finger with a stub ratchet. Also the wiring for the compressor switch it run on it's own circuit (not using any of the factory stuff).
Good news. 1) The compressor should be easy to turn with no sticking and binding. 2) If the compressor was eating itself you would find debris in the oil and orifice tube. With the limited info suppied yesterday, I could not determine if there was a filter medium between the orifice tube and the condenser. 3) A high pressure relief valve for a Sanden is about 5 bucks. Verify this is the correct part. https://www.finditparts.com/products...xoCXU4QAvD_BwE

Bad news. 1) Can't find a pressure rating for the high-pressure relief valve. 2) Only 2 ways I know of to confirm the compressor is good. One involves a $5000.00 test bench. The other is on the car and detailed in section 7 of the attached pdf. I suggest you read through the pdf. The compressor must be forced to output 350 psi. Details are in pdf. If it passes and the oil is relatively clean and not black, the compressor can be put back into service. Their words, not mine. 3) To test the compressor, it must be mounted and fully evacuated, oiled, and charged. That's the gamble. 4) If your oil is metal flake you can expect to find it throughout most of the system. Mostly in the condenser. If you ave a parallel flow condenser, you'll need to replace it because they are nearly impossible to clean properly and plug up easily. A blockage can close a flow channel because the channels are tiny compared to a tube-type condenser. 5) Metal flake oil? Flush the entire system excluding orifice tube, compressor, accumulator. 6)Replace accumulator any time you open the system,

Drain, capture then measure your compressor oil. Turn the compressor shaft to get all oil out. Check the condition of oil. Metal flakes? No bueno. Black oil means oil has been overheated. No bueno.

I don't understand your wiring issue of the high-pressure switch. (NOT SMART AZZ OR DEROGATORY) Do you understand it and can you be sure of your work or do you need help? Maybe you can sketch a diagram and post a picture.

Make sure you purge your a/c gauge lines any time you hook them up.
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File Type: pdf SANDEN AC COMPRESSOR SERVICE GUIDE AND SPECS.pdf (1.64 MB, 5 views)
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post #11 of 18 (permalink) Old Aug 17th, 19, 7:57 AM Thread Starter
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Re: AC compressor question

Quote:
Originally Posted by DUTCH MAX HEADWORK View Post
Drain, capture then measure your compressor oil. Turn the compressor shaft to get all oil out. Check the condition of oil. Metal flakes? No bueno. Black oil means oil has been overheated. No bueno.

I don't understand your wiring issue of the high-pressure switch. (NOT SMART AZZ OR DEROGATORY) Do you understand it and can you be sure of your work or do you need help? Maybe you can sketch a diagram and post a picture.

Make sure you purge your a/c gauge lines any time you hook them up.
The cycle switch is in the accumulator and binary switch is on the high side hose near the evap core, I can confirm that the low pressure cut off (30 psi) does work, with no Freon in the system clutch will not engage. Oil still looks good no flakes, I did find 2 small threads of metal in the orifice tube though.
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Last edited by Dean; Aug 17th, 19 at 10:36 AM.
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post #12 of 18 (permalink) Old Aug 17th, 19, 10:34 AM
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Re: AC compressor question

So the high pressure cut off switch is in the liquid line, not the hot gas line then?

Quote:
Originally Posted by sampoerna415 View Post
Whoops, you are right Dutch I'm using an accumulator not a dryer I used the wrong word for that. There has been a bit of a squeak from either the compressor or belt tensioner, but it would go away after a few minutes. Now the compressor seems unusually easy to turn, there is a slight drag but I can turn it with one finger with a stub ratchet. Also the wiring for the compressor switch it run on it's own circuit (not using any of the factory stuff).
No drier means no filter in the refrigerant flow ahead of the orifice tube.
A drier is a filter-drier.

Quote:
Originally Posted by sampoerna415 View Post
Pretty sure I found the issue, I was checking the electrical system and the relay I'm using for the condenser stops working after about a minute, changed the relay and it's working correctly now. Still scratching my head as to why the binary switch didn't catch this. Maybe the setting is too high? The low pressure shut off is working on the switch. Perhaps 406 psi shut off on the switch is too high? Anyone know what the pressure relief valve is set to on a R4 compressor?
I assume you mean condenser fan stops, which would be my "not enough air flow through condenser reason"

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Last edited by Dean; Aug 17th, 19 at 11:06 AM.
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post #13 of 18 (permalink) Old Aug 17th, 19, 10:54 AM Thread Starter
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Re: AC compressor question

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So the high pressure cut off switch is in the liquid line, not the hot gas line then?
It is in the liquid line, is the proper place for it on the hot gas line?

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post #14 of 18 (permalink) Old Aug 17th, 19, 11:05 AM
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Re: AC compressor question

I think normally it would be at the inlet side of the filter-drier.

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post #15 of 18 (permalink) Old Aug 17th, 19, 11:33 AM Thread Starter
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Re: AC compressor question

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Originally Posted by Dean View Post
I think normally it would be at the inlet side of the filter-drier.
I just sort of copied a more modern system, I was really just trying to learn more about AC systems cause for some reason there isn't much info to find about making an AC system, all the info I could find was on just how to fix existing systems, to be honest I'm surprised it worked at all, I learned a bunch of stuff though. This is the accumulator I'm using https://www.summitracing.com/parts/f...SAAEgJVa_D_BwE
Do I need a filter dryer in the system? I ask because they don't seem to have one on the system I copied. Thanks for the help, I'm still trying to learn this stuff.

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