Buick ReattaDiscuss Bad news good news in the BUICK CLUBS forums; My car's throwing code B447c "Very low refrigerant problem [A/C clutch]" and so my compressor's offline. That's the bad news. On the other hand, my gas mileage is the best ...
My car's throwing code B447c "Very low refrigerant problem [A/C clutch]" and so my compressor's offline. That's the bad news. On the other hand, my gas mileage is the best it's ever been. So I guess the compressor was getting to be a big drag (read under 20mpg highway) on the car. When I tried to refill the converted system with 134a refrigerant, I had to first delete the code so that it would run the compressor (otherwise all I'd get was economy mode). So with the the car running in max A/C I watched the pressure gauge on the refill system jump all around as the compressor cycled on and off. But within a minute the compressor would shut down altogether, slip into economy mode and not draw any refrigerant (gauge pressure spiked).
What do you think? Bad compressor? Or could it be a bad pressure switch (much cheaper!)? Thanks for your ideas.
I had a similar problem with mine a couple years ago,it ended up that the orifice tube was blocked with black stuff,its what they call "black death",i had to clean the complete system and change it to r134,its been working fine since then but sometimes give me b446 and b447 codes,i just reset the codes and cold air comes back.
Are you charging with liquid or gas? what were the low side and high side pressures when it shut down? Any chance you overcharged it?
Thanks for the response.
I was using Quest's R-134a with Sub-Zero. A liquid. Low side pressure before trying to fill was around 15psi. I couldn't measure the high side. The compressor was offline before I tried refilling, so the system wasn't overcharged already.
I may have overcharged it just today, when, with the code cleared, I tried filling and the compressor ran for a minute but then shut off and didn't draw any more refrigerant (the gauge skyrocketed to past 80psi). Now the low-side pressure's at 45psi.
Get everything setup to charge the system. Then disconnect the battery cable for a minute or so, reconnect and try to charge it again. When the freon is low and the compressor pulls the pressure down on the low side of the system, without enough freon in the system, it will trip the low pressure switch and turn off the compressor. I assume you have some type of gage to know when you have it filled properly... don't you?
There is also a high side trip but 45 psi off sounds a little low (should run about 30 psi on the low side running believe the cycle is set at about 26 and much below that it will give an error.
You do have a fan blowing on the radiator ? Blocked front air flow will make the high side skyrocket.
You are not overcharged if the very low pressure warning is triggered. As Padgett said this will trip when the low side pressure falls below 20-25 psi or so. The cycling you describe sounds like you compressor is working. When the compressor cycles off, the high and low side pressures will equalize at around 75 to 85 psi. That is what you describe as a spike. You need to raise the low side pressure to around 30 to 34 psi to keep the compressor from cycling off and on to get a real reading of the system status. Do check that you fans are working properly so that you don't get an excessive high side pressure. Sounds like you can only measure low side pressure so your flying blind on the high side. Hard to determine orifice tube or compressor problems without that reading as well.
You can use the CRT to clear the B447 code in an 89 and probably an 88 too, but 90, 91 owners report they have to disconnect the battery to clear the fault.
You have reported so many readings it is hard to determine where you are at the moment. What is your current static low side reading, and what does it read with the compressor engaged and the system set at max cool? Do both fans run with system on? Do you have a way to measure the high side pressure?
I found it interesting to (on the 89 BInput ) read the low side input and charge it to hold , 0, -/+1 degree Celcius. What I saw was the Compressor cutout-point being -1C*; you don't want your condensate to start freezing.
Go into diagnostic mode on the crt. Go into BMC data, BD28 will be a place to view the AC lowside reading. The AC cuts out at
-2 degrees Celsius. If the freon is to low the temp will frequently fall down into the below freezing range and the AC will cutout out till it warms up to above freezing ,+9 C, then cuts in again. To much of going below freezing at cruise rpm means the B447 code will throw and AC is disabled. Add enough freon to keep the temp from going into the freezing range. Too much and the AC won't get as cold as it can. Too little and it cycles so frequently it never holds a cold point.
I do this so often on other cars I forgot my audience. I hope this clears it up for you.
Last edited by rjfranken; April 11th, 2010 at 10:36.
Reason: data
Bob Means Cha/Tea.
My Car 89 Blue/Blue Coupe, 89 Silver/gray sunroof parts car Wife car 90 White/blue sunroof white/tan parts car
All that about the Low Temp Sensor may be true on other cars and maybe the Reatta. But what signals the BCM to cut off the compressor, under low freon conditions, on the Reatta is the low pressure switch (located on the passenger side firewall under the plastic cowl). It is nothing more than a switch and does not measure temperature. Once the BCM cuts out the compressor to prevent damage, and gives an error message, the code (B446, B447, or B448) must be reset or the battery cable disconnected before the compressor will engage again.
The Low Temperature Sensor comes into play after you have enough freon pressure, on the low side of the system, to keep the contacts closed in the Low Pressure Switch while the compressor is running. I believe what you are talking about is what causes the compressor to cycle while the system is working as it should.
Hey, it's a way to get the proper amount of freon in there without an evacuation and charge by weight. I just said I found it interesting.
The topic is charging the AC.
I have gauges and both methods work. I like to see what the computer is "thinking".
Last edited by rjfranken; April 18th, 2010 at 21:41.
Bob Means Cha/Tea.
My Car 89 Blue/Blue Coupe, 89 Silver/gray sunroof parts car Wife car 90 White/blue sunroof white/tan parts car
Hey, it's a way to get the proper amount of freon in there without an evacuation and charge by weight. I just said I found it interesting.
You may be right in that respect. My comments were in the context of what it takes to keep the compressor running long enough to get freon in a system that is in a low pressure condition. I thought that is what this thread is about.
To much of going below freezing at cruise rpm means the B447 code will throw and AC is disabled. Add enough freon to keep the temp from going into the freezing range.
You cannot add enough to keep the temp from going into the freezing range without the Low Temperature Switch circuit being completed. (See yellow highlight in photo below). Once the BCM senses the Low Pressure Switch circuit is open and sets a code the ECM will not provide a ground to the Compressor relay until the code is reset. (See pink highlight in the photo below.)
You may be correct in saying the Low Temperature Sensor could be used as a means of getting the correct amount of freon in the system. I prefer using A/C gages over evacuation and weighing the charge but to each his own.
Then disconnect the battery cable for a minute or so, reconnect and try to charge it again. .... I assume you have some type of gage to know when you have it filled properly... don't you?
I've been clearing the code computerwise and will try the battery disconnect, but would like to know what advantage it offers.
Yes, I have a gauge with a low-side only connector that came with the refrigerant.
If you can clear the code thru the CRT that's the way to go. Many 90s owners reported that they can't clear it that way they need to disconnect the battery to clear it. There are disadvantages to doing that as you clear your radio presents, clock time, etc. Why do that if you don't have to.
Having only a low side gauge limits you ability to diagnose some AC problems but since you were low on freon it's worth a try.
What is the upper pressure indicated on your gauge dial? Static pressure will probably peg it if it's only in the 65-75 psi range.
Connect can with gauge to low side port. It's wise to bleed a little freon thru the line just before you connect it to purge the air from the line.
Static pressure should be upwards of 75 psi which will probably peg your gauge or close to it.
Clear B447 code from BCM with CRT and start car.
Turn Climate Control to MAX COOL and Auto fan which will be high.
You should hear the AC clutch click in and the low side pressure will drop.
Make sure your condenser and radiotor fans are running when the AC is turned on with engine running.
Read low side pressure with compressor engaged. It needs to be over 20 to 25 psi for compressor to stay engaged.
You first goal is to get low side pressure to be above 25 psi so that compressor stays engaged and you don't have to fight the low pressure cut out issue. One can of freon should get you to that point.
If your pressure is very low you can hold the can upside down to insert liquid into system to start. As pressure builds and the temp and pressure of the freon in the can lowers the transfer of the freon will slow down. Shake the can holding it horizontally side to side and warm it up to improve the flow to get the pressure up to where you need it. At some point the pressure in the system and can will be the same and it will no longer charge. I tap the can with my fingernail and listen for the metal ping to tell there is not any solid freon left. Can will stop being cool to the touch when the transfer stops also.
After you get to the point that the compressor stays engaged, you can then work on optimizing the amount of charge to get peak performance. You can use Bob's suggestion to read the low side temp input to the BCM. You will probably end up with a low side pressure of between 30 to 34 psi if all goes well. Depending on how low a charge you started out with, you may need a second can of freon to complete your charge. It would be best to have an additional electric fan available to put in front of radiator/condenser to simulate airflow running down the road, and raise the RPMs to 1500 to optimize the charge, but that is probably overkill if all your trying to do is get the AC up and running.
.... What is the upper pressure indicated on your gauge dial? Static pressure will probably peg it if it's only in the 65-75 psi range.
80psi.
Originally Posted by Mc_Reatta
.... Static pressure should be upwards of 75 psi which will probably peg your gauge or close to it.
Static pressure was 45-50psi.
Originally Posted by Mc_Reatta
.... Read low side pressure with compressor engaged. It needs to be over 20 to 25 psi for compressor to stay engaged.
You first goal is to get low side pressure to be above 25 psi so that compressor stays engaged and you don't have to fight the low pressure cut out issue. One can of freon should get you to that point.
Low side pressure with compressor engaged was 35psi, and went to 10psi when the compressor cycled off. Pretty consistent range.
Started filling as suggested and got it fluctuating between 25 and 50 psi, until the code threw the climate control into economy and shut down the compressor.
Static pressure now reads 55psi.
I think I've pretty much emptied the 18 fl oz can. There was a lot of liquid refrigerant bubbling out when I released it from the low-side port and when I released the pressure off the gauge.
Problem here in soCal right now may be that it's cloudy in the mid to high 50s. Doesn't seem to me to be the best ambient temperature for trying a refill. Might have to try again when warmer?
So, I'm left with two questions: a) If the refrigerant was way low, then could it take more than 18 fl ozs? b) Would a low refrigerant level cause the car to get worse fuel mileage, even if the a/c wasn't being used? That is, would the compressor somehow create a horsepower drain?
You were and still are very low on freon. If you have a leak, what you're doing now is all for naught. Since you can't draw a vacuum it will be hard to figure out if a leak was why your level was so low.
55 deg ambient is pretty low to be measuring pressures. I might suggest you add remaining freon in your can into the system so you don't waste it by repeating the code clearing and filling procedure again. When you get all of it in, take a last measurement of the static pressure and jot down for reference. When the weather warms up some more, you can read the static pressure again and see if it is the same or higher than what is is now. That will give some indication if you have a leak.
Lowest info I have on what your low pressure should be is: at 60 F --28-38 psi, so your pushing the limit in the 50s.
It takes between 24 and 36 oz to fill a completely empty system. Try to remove the low side connection as quickly as you can to prevent venting your freon from the port.
Car mileage would not be lower due to the compressor not running. The pulley will just freewheel with almost 0 load on the belt assuming it is not defective mechanically. Only if the clutch is engaged and the compressor running would the mileage go down due to the load of the compressor on the engine.
That may not have been liquid freon you saw being released, but the oil in the charge. Kind of looks yellow green like Mountain Dew and of course is slick to the touch. Color is to aid in leak detection. Freon is clear and looks like water spray which evaporates very quickly with no residue.
Sounds like you are making progress if you don't have a leak. One more small (12oz) can will probably get you to where you need to be if you were up to 25 psi at the lowest.
when you guys finish where can I come to have you fix my problem. I am from the generation when you had a clear glass sight tube. No compressor shut down. You just filled the system until the glass ran clear. I have replace the one sensor, top side of pass. The other sensor if taken out would let all of the r12 out. My compressor shuts down before I can get any r12 in. It used to take a can every 2 or 3 years. I did get one can in 2 years ago. I might even drive the car if the a.c. worked...........ken
Kenny, assuming the compressor and compressor relay are in good condition, you can unplug the low pressure switch, install a jumper wire in the connector to bypass the low pressure switch, then the clear codes in the computer or disconnect the battery for a minute to get the compressor to engage again.
With the jumper installed, and the codes cleared, the compressor will run as long as you need to get enough freon in the system to keep the low pressure from kicking out the compressor.
Once you have the system filled enough to start cooling you can remove the jumper and reconnect the low pressure switch.
Not sure if they got rid of sight glasses to discourage shade tree mechanics from working on their own AC's or it was just an unintended consequence. But it sure did make it harder unless you had invested in some gauges etc.
Usually hooking a full can of freon up to the low pressure port will supply enough pressure to trigger the low pressure switch and let the compressor run. Have this connected before you start the compressor. Need to keep shaking the can and try to keep it warm to get enough in to keep it running if the system is real low. Changing the orientation of the can from sideways to upside down and back and repeating will let some liquid freon in which will get pressure built up faster too.
Following Ronnie's advice will definitely make sure the compressor is running so you can get it in. I just hope you don't have a large enough leak that it won't stay around.
Sounds like you are making progress if you don't have a leak. One more small (12oz) can will probably get you to where you need to be if you were up to 25 psi at the lowest.
Update: Since the weather's warmed up a bit to the mid 60s I decided to measure the low-side pressure. It came it at 75psi! Then I thought I should clear the b447c code to see if the A/C stays on. Am glad to report that it doesn't switch over into Economy, and does blow cold, though it cycles on/off a lot (probably because of low ambient temp?).
It did throw a code after several minutes: b446c, which I take it means that there's some refrigerant now in the system, but still not enough. Took a few more low-side readings: 60-65psi.
Questions: Why would it be sensing a low pressure when the low-side port reads so high (too high)? Should I go ahead and add more anyway?
The computer is saying you're still low on freon but hard to diagnose for sure at such a low ambient temp.
The 60 psi low pressure readings are puzzling. Either the gauge is way off, or your taking readings when the compressor in not engaged. As the compressor cycles the gauge will span a wide range of pressures. The one your interested in the the lowest one displayed. When the compressor cuts off the pressure will rise until it reengages and then the reading will drop again. The lowest reading is the truel low pressure.
The way your system is acting I would think you are in the mid to high 20's
I'd wait some more until the ambient temp gets well into the 70's before checking again. No sense trying to chase your tail. Pressure and temperature are directly related so your pressure will rise on it's own as the weather gets warmer.
If anybody is working on their A/C it would not hurt to bleed the charging hose by holding the can upright and open the valve for a couple of seconds to purge the air out of the hose before hooking it up to the low side. Even more important if you are using a set of gauges and have two long hoses.
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1990 Reatta Coupe, 1971 Buick Skylark Convertible Miami FL.
Originally Posted by Richard D 
