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Old 06-02-2020, 07:51 PM
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A/C trouble shooting question

Evening Hot Rodding gurus, I have some A/C questions I need some help with.

Lets start with the basics: 07 Saturn Sky, 2.0 turbo, manual, 100000 miles.

Problem: The A/C shuts off because of high pressure, once pressure drops it will come back on.

I have the factory service manual and this is what led me to high pressure statement above.

The facts: todays temp outside 86 deg, 49 percent humidity

Service manual says gage should read 34-46 psi low side / 187-242 psi high side

Actual gage readings 45psi low side / 280 psi high side, high side would climb as high as 300 psi and switch would shut down system.

Using the trouble shooting guide lead me to section shown below.

"Feel along the surfaces of the following high side components:
The compressor discharge hose The condenser The liquid line between the condenser and the expansion device

Did you detect an abrupt drop in temperature along the surfaces of any of the listed components? "

Now to the question 1: what is an abrupt drop in temperture?

Also in order to check these componets I used a laser temp gun because there is no way the get a hand on these lines while car is running.

Here is what I found:

1) From compressor to the condenser:
Hose temp at compressor out =157 F
Hose temp into condenser = 118 F

2) From condenser to the TXV:
Hose/line out of condenser = 142 F
Hose/line into TXV = 124

I cannot see the condenser itself to get a reading across the coils,

Question 2: with facts above where is my restriction? I am thinking the discharge hose would be the best place to start for 3 reasons, temp change, price and easy to get too, condenser would be a pain.

Added Note: while looking over system I can see some oil seepage at the discharge hose to condenser connection.

Parts already replaced: TXV and dryer
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Last edited by 95 Truck; 06-02-2020 at 08:02 PM.
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Old 06-03-2020, 05:53 AM
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Quote:
Originally Posted by 95 Truck View Post
Evening Hot Rodding gurus, I have some A/C questions I need some help with.

Problem: The A/C shuts off because of high pressure, once pressure drops it will come back on.

I have the factory service manual and this is what led me to high pressure statement above.


the listed components? "

Now to the question 1: what is an abrupt drop in temp.





Question 2: with facts above where is my restriction? I am thinking the discharge hose would be the best place to start for 3 reasons, temp change, price and easy to get too, condenser would be a pain.

Added Note: while looking over system I can see some oil seepage at the discharge hose to condenser connection.

Parts already replaced: TXV and dryer
Im no expert, but I know a little...
The most common cause of high pressure spikes I see is lack of air flow over condenser.

Does it work good driving down the road, then blow warm at the traffic light or drive thru? If that is the case, one or both of your cooling fans is not working and there is a simple procedure to test those.

You have already replaced the expansion valve, those will make noise in the dash after the car is shut off usually if they are bad. But its ok to put a new one in. New dryer is ok too.

The temp difference I feel for is the low side coming out of the dryer. It will be cold if your compressor is cycling and working good. Don't ever touch the high side because those jokers run hot!

As far as the oil leaking. If it is in fact PAG oil it should be green and fluorescent in most GMs from the factory, and that will be a leak.

Did you pull a good vacuum? Also let it sit for over an hour and watch the needle. That will let you know if you have a leak.

Now thinking about your charge...
You don't want to overcharge at all. More is not better.

Edit. Also I don't think there is a restriction. You just have high pressure. Low side works best at 40. It really sounds like fans not working or compressor is getting weak.

Last edited by Excellenceautosoluti; 06-03-2020 at 05:58 AM.
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Old 06-03-2020, 04:22 PM
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Check the airflow across the condenser as suggested.

The compressor is good if it can pump the high side to 300 PSI


Take a garden hose and spray the condenser with the system running when the pressure gets to 250-275 . See if it drops off .

Spraying water across it will cool it fast and drop the pressure quickly.

If it drops the pressure fast , then you likely have poor airflow.
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Old 06-03-2020, 05:55 PM
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JMHO, two other things that can cause excessive high side pressures, Too much refrigerant, Too much oil.
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Old 06-03-2020, 07:36 PM
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Quote:
Originally Posted by 36 sedan View Post
jmho, two other things that can cause excessive high side pressures, too much refrigerant, too much oil.
yes ^^^^^^^^^^^^^^^^^^^^
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Old 06-03-2020, 07:41 PM
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Thanks for the help guys, I seen ExcellenceAuto post about possible over charge this moring and tonight I pulled some charge out of it and now the low pressure side is reading 35 psi and high side is 200 psi. Todays temp 84 F and 50% humidity, which is with in specs.
The unit is still cycling on and off, but I think now it might be as you guys have said its air flow across the condenser. I will take it for a ride tomorrow and see how it cycles.

Also I think 36 sedan might be on to something while pulling some refrigerant out via the high side, I got a good slug of oil.

Again thanks guys for the help, I will update post, after a drive.
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Old 06-04-2020, 07:43 AM
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With both numbers too high, looks like you were over charged... now almost under charged...

Compressor cycling on and off is normal... should be less cycling with controls in Max A/C position...
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Old 06-06-2020, 06:08 AM
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Ok here is an update, took car out yesterday and car is still doing the same thing it has since I bought it.
While driving the A/C will stop making cold, clutch/compressor disengages, drive a few minutes/miles and it clutches back in. When it drops out, it drops out long enough that the interior will no longer be cool/cold, when it kicks back in, it will run just to the point of the interior getting comfortable.
This took place while on freeway at 80 mph, air temp out of vents is 60 deg, it does same in city traffic.

My first thoughts back then was the TXV and Dryer were plugged, so I changed them and pulled a over night vacuum, charged the system. The with it cycling on and off made me think low charge so I add more, which in hind sight lead me to over charge issue.

So as I mentioned in post other night, I pull out some charge and got the pressure down to service manual spec.

One thing that was brought up is to much oil, which when I pulled some charge out other night I got a slug of oil with it. I have been thinking this out, correct me if am wrong, with to much oil there is a slug of it traveling through the system, when it gets to the TXV its like a syurp vs a water and TXV kind of acts like its plugged up, causing restriction, increasing pressure and disengaging clutch, once oil flows thru TXV pressures returns to normal and system returns to normal.

Is my thinking correct?

Now as for pulling off excess oil, my thoughts are I need to open system and blow thru high side compressor to condenser hose?

The A/C compressor on this car is at the bottom of engine (lowest point in sytem), the hose from compressor to condenser comes across top of compressor and stays parelle to the ground. My thinking is the oil will drain down to this low level and be the best place to drain. I am also thinking because hose is on top of compressor the compressor will stay full of oil it holds.

Any thoughs on if this is best way to pull out extra oil if there is extra?
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Old 06-06-2020, 07:02 AM
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Why would it have excessive oil in the system ?
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Old 06-06-2020, 07:08 AM
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If it was mine, I would pull it down again and put the proper amount of refrigerant in it.

Once you have it charged, and then let stuff out you really don't know how much is left in it now. The systems nowadays are really finicky about the charge.

This way you will have a good base starting point, and if it's still acting funky do some troubleshooting after that.
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Old 06-06-2020, 07:13 AM
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Quote:
Originally Posted by 95 Truck View Post
While driving the A/C will stop making cold, clutch/compressor disengages, drive a few minutes/miles and it clutches back in. When it drops out, it drops out long enough that the interior will no longer be cool/cold, when it kicks back in, it will run just to the point of the interior getting comfortable.
This took place while on freeway at 80 mph, air temp out of vents is 60 deg, it does same in city traffic.
As I mentioned above, the compressor cycling on and off is normal, but not to the extent you're seeing...

I'd concentrate on what is turning the compressor off and/or keeping it off:

A thermostat in the in dash controls is satisfied and turning it off?

The high pressure limit switch is defective and turning it off at too low a pressure? Or not turning it back on soon enough?

High and low pressures used to be separate switches, but now usually combined into one...

Many people add only refrigerant without also adding oil to replace what was lost with the refrigerant and the compressor seizes up...
.
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Old 06-06-2020, 09:51 AM
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Quote:
Originally Posted by 95 Truck View Post
While driving the A/C will stop making cold, clutch/compressor disengages, drive a few minutes/miles and it clutches back in. When it drops out, it drops out long enough that the interior will no longer be cool/cold, when it kicks back in, it will run just to the point of the interior getting comfortable.
JMHO, but this sounds like moisture in the system freezing up the expansion valve, then thawing out and recycling.

If you have not changed any components that would add oil (compressor), I would move past that and start over with a new dryer and vacuum system with heat elevated. If the temperature is cold you will never get the moisture out, vacuum only lowers the boiling (vapor) point, elevated temperature will allow the moisture to be removed.
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Old 06-06-2020, 11:41 AM
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Different cars, same manufacturer will use different styles. Remember this.


The compressor clutch might be wearing out. On most Ford products, you can reduce the shims between the clutch and compressor to reduce the excess clearance. Depending on your compressor you might be able to do the same. Some vehicles use a line filter, when those start to clog up they will increase the line pressure and you will have the situation you are talking about.


When you vented, you may have taken out too much refrigerant. My fix after some of the tests mentioned would be to drain the system, vacuum it down - check for leakage, Make sure of the correct amount of PAG oil and refill the system refrigerant according to specs - normally noted somewhere under the hood on a sticker.
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Old 06-07-2020, 06:53 AM
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ok sounds like its time to empty system and pull a hard vacuum, I will park car in sun this tuesday (going to be 91 here) to make sure moisture if any will boil off.
I replaced dryer just after I got the car has been been replaced.

Buzz I also was thinking high pressure switch malfunction, I tried to jump it out one time and pissed off computer and stalled the car, it is a 3 terminal switch, not the old simple two terminal.
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Old 06-07-2020, 07:20 AM
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Quote:
Originally Posted by 95 Truck View Post
I replaced dryer just after I got the car has been been replaced.
JMHO, Every time the system is opened the dryer should be changed. The dryer is insurance, it traps moisture left in the system the evacuation process didn't/couldn't remove (there are lots of bends and turns to trap moisture and lots of cold metal enclosing it).

Not changing the dryer when the system has been opened is like gambling with the odds stacked WAY against you.

http://www.jbind.com/pdf/Cross-Refer...ling-Temps.pdf
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