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  #1  
Old 24th July 2012
milehighsaab93 milehighsaab93 is offline
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Default Intermittent AC problem

Hey guys,

I know there are a lot of AC threads out there, and I have searched around, but can't seem to find anything to answer my question.

The AC in my 01 9-3 is having some issues. When I'm driving in town the A/C works fine. Its not Ice cold, but it does the job and I dont really wanna pay to recharge it, but I start experiencing intermittent problems when I'm driving on the highway.

I live in Colorado where its been around 100 deg. F almost every day for the past month. When I get on the highway the air will blow cold (as cold as in town) for a little while, but then it will start to "cycle" and blow hot air for a while followed by cold air, followed by hot, etc.... One "Cycle" of hot air will last a couple of minutes and then the cold will come back for a minute or so. any thoughts? My guess is compressor related, but I'm an A/C noob.

THanks
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  #2  
Old 24th July 2012
win_k win_k is offline
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Quote:
Originally Posted by milehighsaab93 View Post
Hey guys,

I know there are a lot of AC threads out there, and I have searched around, but can't seem to find anything to answer my question.

The AC in my 01 9-3 is having some issues. When I'm driving in town the A/C works fine. Its not Ice cold, but it does the job and I dont really wanna pay to recharge it, but I start experiencing intermittent problems when I'm driving on the highway.

I live in Colorado where its been around 100 deg. F almost every day for the past month. When I get on the highway the air will blow cold (as cold as in town) for a little while, but then it will start to "cycle" and blow hot air for a while followed by cold air, followed by hot, etc.... One "Cycle" of hot air will last a couple of minutes and then the cold will come back for a minute or so. any thoughts? My guess is compressor related, but I'm an A/C noob.

THanks
Could be a couple things:

1st, If the refrigerant level is low, at higher engine speeds (and compressor RPM's) the pressures drop too much and the low pressure cut out switch will shut off the compressor. As pressures equalize, (while the a/c blows warm air) the pressure switch will re-enable the compressor and it'll run for a while before repeating the process.

2nd, It's possible the receiver/drier is clogged and not allowing sufficient refrigerant through the system. (same cycle as above)

3rd, It's possible the expansion valve is clogged or malfunctioning and doing the same thing.

4th, the temp switch in the a/c evaporator is detecting too low an evap temp and is shutting down the a/c -- I'd expect this to be a longer time cycle than the others. Once the evap warms back up, the switch re-enables the compressor.

As whacky as it sounds, low refrigerant levels can cause the evap to get too cold close to the expansion valve and cause the symptoms you're seeing.

I'd think your symptoms best match this scenario.

Lastly, it is possible that there's an electrical fault causing the problem, but I'd start with the refrigerant level and that temp switch (NOT a fun part to get to BTW)
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Old 24th July 2012
milehighsaab93 milehighsaab93 is offline
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Quote:
Originally Posted by win_k View Post
Could be a couple things:

1st, If the refrigerant level is low, at higher engine speeds (and compressor RPM's) the pressures drop too much and the low pressure cut out switch will shut off the compressor. As pressures equalize, (while the a/c blows warm air) the pressure switch will re-enable the compressor and it'll run for a while before repeating the process.

2nd, It's possible the receiver/drier is clogged and not allowing sufficient refrigerant through the system. (same cycle as above)

3rd, It's possible the expansion valve is clogged or malfunctioning and doing the same thing.

4th, the temp switch in the a/c evaporator is detecting too low an evap temp and is shutting down the a/c -- I'd expect this to be a longer time cycle than the others. Once the evap warms back up, the switch re-enables the compressor.

As whacky as it sounds, low refrigerant levels can cause the evap to get too cold close to the expansion valve and cause the symptoms you're seeing.

I'd think your symptoms best match this scenario.

Lastly, it is possible that there's an electrical fault causing the problem, but I'd start with the refrigerant level and that temp switch (NOT a fun part to get to BTW)

Thanks for the reply. I have checked the pressure , but only with a "re-fill" bottle on the low pressure side. It read in range, but I dont know how much to trust those things. If I were to get my hands on a manifold pressure gauge set what pressures should I see?
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Old 24th July 2012
win_k win_k is offline
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With the engine at about 2000rpm, you'll want to see 38 psi or so.

If you do find a manifold gauge set, see if you can also get a good temp gauge.

There's a temp scale on the gauge. The "real" temp of the retutn pipe at the firewall should be about 10 degrees warmer than the scale for the indicated pressure.
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Old 24th July 2012
jitsjaf2009 jitsjaf2009 is offline
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Check Harbor frieght, they have a set for 134a at about $50. A refrigeration friend of mine has used them a couple times and said they are good to go. It is not cheap, but nothing is any more. I rarely use my A/C, just put the top down and hope the traffic lets me cruze. Love my Saab
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  #6  
Old 25th July 2012
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steviethev steviethev is offline
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Quote:
Originally Posted by jitsjaf2009 View Post
Check Harbor frieght, they have a set for 134a at about $50. A refrigeration friend of mine has used them a couple times and said they are good to go. It is not cheap, but nothing is any more. I rarely use my A/C, just put the top down and hope the traffic lets me cruze. Love my Saab
You know, I have those exact same ones. They do work pretty well. Use a 20% off coupon (which can be found just about anywhere) and it's around $40. I made that money back quickly using them on friends' cars...

As for this thread, I had a very similar problem with mine. A recharge of the system, and checking/verifying the pressures were correct, and it's been really nice ever since. It was amazing that I didn't notice how 'not cold' the air had been. Now it's really cold. Almost as cold as the wife's 2011 Corolla...
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Old 25th July 2012
milehighsaab93 milehighsaab93 is offline
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So I got myself some A/C gauges.... and I'm not exactly sure what it should be reading. I took some pictures of the gauges and wanted some feedback.

The pictures are attached. Sorry they aren't the best quality. Here's what they were:

Low press off - 88 PSI

High press off - 125 PSI

Low press idling - 32 PSI

High press Idling - 155 PSI


Whats the exterior black scale used for? It is rated in + or - degrees C.

THanks for all the help
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  #8  
Old 25th July 2012
win_k win_k is offline
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Your running pressures strongly suggest the system is low on refrigerant.

The a/c off pressures don't make sense, they should be the same on both gauges.

That temp scale is the temp the refrigerant should be for the pressure.
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  #9  
Old 26th July 2012
milehighsaab93 milehighsaab93 is offline
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Quote:
Originally Posted by win_k View Post
Your running pressures strongly suggest the system is low on refrigerant.

The a/c off pressures don't make sense, they should be the same on both gauges.

That temp scale is the temp the refrigerant should be for the pressure.
Ill try to re-check the non running pressures tomorrow. I think I should have checked the non running pressures right off the bat. I ran it first while checking the pressures, and then tried to check them again without it running. Probably not the right way to do it.

What is the proper range for high and low pressures with the car running? Ive heard 25-35 for low and 200-350 PSI for high. That seems like a very large range....
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Old 26th July 2012
win_k win_k is offline
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Quote:
Originally Posted by milehighsaab93 View Post
Ill try to re-check the non running pressures tomorrow. I think I should have checked the non running pressures right off the bat. I ran it first while checking the pressures, and then tried to check them again without it running. Probably not the right way to do it.

What is the proper range for high and low pressures with the car running? Ive heard 25-35 for low and 200-350 PSI for high. That seems like a very large range....
I'd look for 35 to 38 psi on the low side, 190 to 225 on the high with the radiator fan running at high speed and the engine at 2000 rpm.

If low pressures fall below 30 psi under any conditions, you'll get ice build up on the evap coil (quite possibly the problem you're experiencing now)

High pressures can vary pretty significantly with both ambient and in-car temps 250 to 275 psi is the start of the too high range, 300 starts the "excessive" range.
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Old 26th July 2012
IOP9-3Guy IOP9-3Guy is offline
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Here's a good primer on what some of the gauge readings mean to the system. I've been poking around the site, and there's a ton of good info available.

Tom

http://www.aircondition.com/tech/questions/82/
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Old 26th July 2012
milehighsaab93 milehighsaab93 is offline
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Quote:
Originally Posted by win_k View Post
I'd look for 35 to 38 psi on the low side, 190 to 225 on the high with the radiator fan running at high speed and the engine at 2000 rpm.

If low pressures fall below 30 psi under any conditions, you'll get ice build up on the evap coil (quite possibly the problem you're experiencing now)

High pressures can vary pretty significantly with both ambient and in-car temps 250 to 275 psi is the start of the too high range, 300 starts the "excessive" range.
Alright, I re-did the tests this morning.... much different results. This is after the car sitting overnight. I hooked the gauges up without starting the car at all and got these readings:

Low Press: 65 PSI

High Pres: 65 PSI


Started the car and left the A/C off. Got the same readings. Turned the A?C on full blast and waited for the radiator fan to come on and the pressures to equalize. Got these readings:

Low Press: 15 PSI

High Press: 110 PSI

According to whats been said these are obviously low readings. I need to fill the system with freon, but am not completely sure how to go about that. If there is already a thread for that please just point me that way....

The yellow hose hooks in two places to pressure test. Im assuming I leave the downward connection attached to the gauges and remove the horizontal connection (it has a valve in it) to connect it to the can. How do I operate the High and Low pressure valves right below the gauges? Do i open them both to fill it?

Thanks for all the help.... this is my first experience working on an A/C system at all.
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  #13  
Old 26th July 2012
IOP9-3Guy IOP9-3Guy is offline
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FIRST: if you're not comfortable filling the AC, take it to a shop. It's usually only a few dollars more, and you can probably watch them fill up the system.

SECOND: FILL on the LOW SIDE ONLY!! if you open both sides, or even just the high side, you'll get over 200 PSI at the refrigerant can, and the bottom will blow out of it.

Hook up both gauges with the valves to the gauges closed. Attach middle hose to refrigerant can (you may have to buy a tap for this).

Turn Engine on. AC to High, Full Fans, Etc. Once compressor cycles, tap the can (screw all the way down, then back up). Open valve to low side on gauge manifold.

Add refrigerant until low and high pressure are in the 'good' range for ambient temps.

Close low side valve. Close tap on can. Remove gauges. Test Drive.

Some refrigerant cans now come with their own fill valve and low pressure gauge. It's up to you if you'd like to use this setup. I would still use your gauges to monitor the high pressure port.

Also, I like to run some refrigerant through my hoses before it goes into the system. That way, there's less air and moisture that the AC system will have to deal with. With the car off, I open up both the low and high side valves just enough to have some refrigerant come through the middle hose, then I turn both valves off. when I tap a new can, I loosen the fitting of the middle hose and release enough refrigerant to just come out of the hose fitting, then tighten it up. It could be overkill, but I think it;s better than pumping in a hose full of air and moisture before the refrigerant enters the system.
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Old 26th July 2012
IOP9-3Guy IOP9-3Guy is offline
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Quote:
Originally Posted by milehighsaab93 View Post
I hooked the gauges up without starting the car at all and got these readings:

Low Press: 65 PSI

High Pres: 65 PSI
What was the ambient temp when you hooked up your gauges?

The static pressure within the system can indicate charge level, although it is not an absolute determination as to whether your system is adequately charged or not.
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Old 26th July 2012
milehighsaab93 milehighsaab93 is offline
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The ambient temp was about 75 degrees when I hooked everything up this morning. I understand that effects what static charge you will see. Does that PSI reading seem low for it being about 75 outside?

Thanks for the info on how to fill the system. I have used the "re-charge" kit to fill the low side before, but never the manifold gauges. I'm just going to take it slow and do it myself. I figure since I have the set of gauges now I should figure out how to use them properly. I've got a few friends who are ASE certified so maybe Ill have one of them come help me out.
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Old 26th July 2012
IOP9-3Guy IOP9-3Guy is offline
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read through the link I posted earlier. Here's an excerpt:

What static pressure should I expect to see when I hook up my gauge set.
Each refrigerant has it's own static pressure at every corresponding degree in temperature. The important thing to keep in mind is static pressure changes based on temperature. Any change of temperature brings with it a change of pressure. The greater the temperature, the greater the pressure. You can use a refrigerant pressure chart to find static pressures at various temperatures. Static pressure will not be used to determine if a system is fully charged. Using the chart below, if the R-134a system has a static pressure of 88 psi at 80 degrees F., we can then assume the system has some amount of liquid refrigerant. The system may be full -or - may not be. At the same temperature, if the system showed only 75 psi, we could say with confidence, the system is low. This is because static pressures shown on a temperature chart would show inadequate pressure for the presence of any liquid refrigerant.
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Old 26th July 2012
milehighsaab93 milehighsaab93 is offline
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Thats a really good site. I read through the whole thing... the actual chart is missing, but just looking at that example in that paragraph it seems like the pressure should be higher than the ambient temp when it's static. Ill search around for a good pressure chart.
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Old 26th July 2012
IOP9-3Guy IOP9-3Guy is offline
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I think the chart on this link will show static pressure for r134-A.

Looks like 65 is a bit low for 75 degrees Fahrenheit.

https://docs.google.com/viewer?url=h...df&chrome=true
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Old 26th July 2012
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This is a common problem with these cars. I had the problem with my 9-3 after my low speed fan resistor failed. I replaced the fan, dryer, compressor and the expansion valve.

My fan resistor then failed on my Viggen and my A/C started cycling, I replaced the fan and the A/C will cycle but it doesn't do it frequently. I think when the low speed fan resistor fails the system runs too hot and ruins the expansion valve. Just a guess.
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