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Old 05-15-2010, 06:58 PM   #1
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Default A/C High-side vs. Low-Side

M'kay...

Compressor is quiet and cycles/runs fine (based on general observation)

System was empty. System ingested 1 and 1/8 cans of coolant charge, and quit sucking any more after that. Air never got cold.

DIAGNOSE:

High Side:
Press in schrader valve, TON of pressurized coolant sprays.

Low Side:
Depressing shrader valve produces nothing.

Discuss.
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Old 05-15-2010, 07:45 PM   #2
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Are you using gauges? If it was empty you need to pull a vacuum before trying to recharge. With the car off the system should equalize according to the ambient outside temperature - for example, about 82 degrees should be close to 100 psi, then drop down when the compressor starts. Gauges will tell you if there is a restriction - low suction/high head pressure.
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Old 05-15-2010, 08:14 PM   #3
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Upon insertion of the first can, the gauge initially indicated about 100psi, and dropped to roughly 95psi. The low-side fitting "froze up" pretty good, that is to say, it developed thin slush/ice on the metal fitting. Shaking the can as instructed resulted in a slight rise in pressure.

Then, after the first can emptied, hooked up the second can. The frozen quality of the metal fitting on the low-side diminished greatly. Gauge then stayed somewhere between 105psi and 110psi, never really fluctuating.

Again, the high side seems to contain all the coolant pressure. The low side, not so much... i.e. no schrader valve reaction, and no cold air out the vents.
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Old 05-15-2010, 08:36 PM   #4
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Did you pull a vacuum?


Possibly a clogged orifice tube. . . . .


My way of diagnose(yes, this is not the EPA way): Let the 134a out, pull vacuum for 45 minutes, fill it up with 1.5 cans(I think that is what ours takes, but I have not done this for a bit). Check low and high pressures. . . . Go from there.
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Old 05-15-2010, 08:56 PM   #5
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Let me clarify on this a tad for the record. This is not on a Z. This is on a 90 Nissan Hardbody P/U. An old R12 system. The compressor appears to be new as is the engine and everything else under the hood as the truck was just purchased recently. NO we didnt pull a vacuum, the system was only open long enough to replace a pinched o ring but has been under positive pressure so there was no indication that moisture or anything else could have gotten in. Now I know this isnt the best/right way to do it, however thats not what 1FSTz is asking.
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Old 05-15-2010, 09:10 PM   #6
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Yes, I probably should have been more clear, but I valued generalized answers from a basic automotive A/C system perspective. This '90 Nissan Hardbody pickup obviously originally came with an R12 system, but understand that I bought it with a new drop-in motor/AC system, etc... all new under the hood.

SO, with that being said, it has obviously been upgraded, as it has R134a fittings on the system.

Conclusively, no a vacuum hasn't been pulled, but yet nor is there a leak even remotely apparent. Hell, even the evaporator actively drips condensation under the truck while the system runs... but no cold air comes out the vents.

Furthermore, and to repeat the previous statements, the low side's schrader valve has no coolant pressure; yet the high side has tons.
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Old 05-15-2010, 09:33 PM   #7
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What device does it use for expansion...orifice tube, expansion valve, capillary tube?
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Old 05-15-2010, 09:56 PM   #8
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Quote:
Originally Posted by fleetmgr View Post
What device does it use for expansion...orifice tube, expansion valve, capillary tube?
I do need to learn more about this specific system.... that being said, I have no idea fleetmgr.

Again, 1990 Nissan D21 pickup with the factory; albeit brand new, crate KR20 engine (the 240SX motor).



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Old 05-15-2010, 10:07 PM   #9
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OK....this is something you need to look at. If it's an orifice tube, it could be plugged. If it's an expansion valve, it could have a broken capillary tube or broken bulb at the end of the tube (this is what controls the valve) or it could be plugged, and if it's capillary expansion, the capillary tube could be kinked/broken or plugged.

Another possibility is moisture in the system causing an ice ball at the outlet of the expansion device.

The other possibility is a clogged evaporator, but that's pretty rare.
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Old 05-15-2010, 10:14 PM   #10
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fleetmgr,

Would you happen to know what kind of expansion device the oldschool R12 systems typically used?

I mean if it comes down to it, I suppose we can disassemble all the lines and flush them.

It just seems as though the solution should be somewhat simple. By saying that, I mean.... We have pressure like a sumbitch coming outta the high side when we press the schrader valve, yet none on the low side.

The main device in between seems to be the compressor, yet the compressor is apparently functioning normally. So, it's like WTF is happening in that short physical distance between the low side --> compressor --> high side ???

MUST be a blockage of sorts!?
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Old 05-15-2010, 10:44 PM   #11
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Quote:
Originally Posted by 1FST-Z View Post
fleetmgr,

Would you happen to know what kind of expansion device the oldschool R12 systems typically used?
Usually a valve or a cap tube.

Quote:
Originally Posted by 1FST-Z View Post
I mean if it comes down to it, I suppose we can disassemble all the lines and flush them.

It just seems as though the solution should be somewhat simple. By saying that, I mean.... We have pressure like a sumbitch coming outta the high side when we press the schrader valve, yet none on the low side.
You have no refrigerant going through the evaporator, so the compressor is cycling on the low pressure switch. Now, with that said though, if you have nothing going through the evaporator, you should be having to jump the compressor straight to the battery in order to get the clutch to engage. If you aren't doing that, then SOME refrigerant is getting through...just not enough to make cold air or develop a positive pressure in the suction line. What happens if you walk away for a couple of hours? Does the suction line show a pressure then, or show any iceing on the outside? If you can walk away, and come back and then it works ok for a bit and then stops again then you have ice forming in one of two places. Either it's at the outlet of the expansion device, meaning moisture in the system (highly likely as you say there is no pressure in the suction line), or the evaporator drain is clogged, and the box is filling with water which then freezes so that you get no airflow across the evaporator. This will shut things down on the low temp switch.

Quote:
Originally Posted by 1FST-Z View Post
The main device in between seems to be the compressor, yet the compressor is apparently functioning normally. So, it's like WTF is happening in that short physical distance between the low side --> compressor --> high side ???
Yes, the compressor is one of the dividers between hi and low sides. The other is the expansion device. One thing to remember about A/C troubleshooting....hi side problems don't effect the low side, and low side problems don't effect the hi side. As you're making pressure, it's not a compressor issue.

Quote:
Originally Posted by 1FST-Z View Post
MUST be a blockage of sorts!?
If it's an expansion valve system, and the capillary tube/thermo bulb that controls the valve gets kinked/broken/plugged then it'll never pass any refrigerant. Same with a capillary expansion system or a orifice tube system. Moisture in the system that freezes = plug.

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Old 05-15-2010, 10:58 PM   #12
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fleetmgr:

Most interesting that you brought up the jumped compressor scenario. Remember participating in this short-lived thread?

http://www.ls1tech.com/forums/genera...-ac-issue.html

So, yes actually... we ended up initially jumping the compressor. It took in that 1 and 1/8th can and then quit sucking it up.

Now with that 1 and 1/8th can in the system, the compressor now kicks on with no problem, jumper removed.

Yet... no cold air, no low side pressure...but apparently enough in some way, shape, or form... to activate the compressor.
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Old 05-18-2010, 08:16 AM   #13
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UPDATE:

Figured I'd update this thread with our findings.

This primarily goes out to all the folks with an upgraded R12 system.

If you experience what we did, the fact that the compressor correctly self-activated was the hint. Cranked the truck the next day and turned on the AC to see what would happen. Low and behold, it had moderately cool air.

We put another can in it, and as this 2nd can emptied, my buddy switched from "Full Face" to "Face and Feet." It made the compressor cycle differently, and like a little miracle, the damned gauge dropped right there in front of us.

Fully charged, ice cold air. WIN.

Conclusion:

When dealing with an older upgraded system, be PATIENT.
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Old 05-18-2010, 10:39 AM   #14
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I almost didnt believe it myself. Congrats to us
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Old 05-18-2010, 11:03 AM   #15
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Congrats on the win but you really need to pull a vacuum if you haven't already. Moisture in the system will break down the compressor oil and in a short time you will be dealing with some "black death." Its absolutely critical to the AC system.
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Old 05-18-2010, 11:03 AM
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