soveryfaraway Posted March 23, 2012 Report Share Posted March 23, 2012 Recently, a message was displayed that refrigerant was very low, and the AC compressor was disabled. A shop checked the refrigerant, said it was fine - plenty of pressure. So, doing a little research, I jumped the low pressure switch, cleared the B1347 code, and the AC compressor kicked on and cooled like a freezer, so I ordered a pressure switch. 20 miles later, with the jumper still intact, the same error appeared. Any ideas on what else can cause this problem (besides an intermittent open in the harness or the computer itself)? I need a new direction. Link to comment Share on other sites More sharing options...
Ranger Posted March 24, 2012 Report Share Posted March 24, 2012 Either you have a bad switch or actually ARE low on refrigerant. How did the shop check the refrigerant charge without clearing the code to enable the compressor? Link to comment Share on other sites More sharing options...
soveryfaraway Posted March 24, 2012 Author Report Share Posted March 24, 2012 The switch is jumped out, please read the text. Not an issue. As to checking pressures, most check them when the units are at rest. Like tires. Or well system tanks. Checking a pressure when a unit is active is mostly discouraged due to the dynamics of the situation, but if anyone can state otherwise, I will certainly be receptive. Link to comment Share on other sites More sharing options...
KHE Posted March 24, 2012 Report Share Posted March 24, 2012 The switch is jumped out, please read the text. Not an issue. As to checking pressures, most check them when the units are at rest. Like tires. Or well system tanks. Checking a pressure when a unit is active is mostly discouraged due to the dynamics of the situation, but if anyone can state otherwise, I will certainly be receptive. A car air conditioner is not a tire or a well tank... If someone concluded the system is full based on static pressures, they have no clue on how to diagnose an automotive A/C system. Unless the shop recovered and weighed the amount of recovered refrigerant, to make sure there was 2.0 lbs. recovered, it is not possible to conclude much from pressures. NOTHING can be concluded from a static pressure reading unless the system is so low on refrigerant that the gages only read 30 psi or so. As for checking the pressures, they have to be checked while the unit is in operation. The correct point to take the readings is right before the compressor shuts off in its cycle - the high pressure side will be at its maximum and the low pressure side will be at its minimum. The Cadillac uses two thermistors to monitor the refrigerant temperature as well as a pressure sensor. Do not jump the pins of the sensors - especially the high and low side thermistors as you can cause damage to the system. When the system says the system is low on refrigerant, 99.9999% of the time, it IS low on refrigerant. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
soveryfaraway Posted March 24, 2012 Author Report Share Posted March 24, 2012 Let us then suppose that the system is low on refrigerant. How does it report that if the low pressure switch is disabled? Is there some other means available to sense that? Link to comment Share on other sites More sharing options...
KHE Posted March 24, 2012 Report Share Posted March 24, 2012 Let us then suppose that the system is low on refrigerant. How does it report that if the low pressure switch is disabled? Is there some other means available to sense that? The syetem uses thermisters to obtain the temperature of the refrigerant on the high side and the low side of the system. That is before and after the orifice tube respectively. If the system detects an improper condition, the ACM disables the compressor so that it will not run. This is so the compressor does not self destruct. The thermisters rarely fail. One of the most common failures is someone installs the orifice tube backward - that will damage the low side thermister and set the code for either an open or shorted low side temperature sensor. The low pressure sensor disables the compressor in the low refrigerant condition. There is also a high pressure cut off sensor that shuts the system down in the event of an overpressure condition. The proper way to diagnose and repair the system is to reconnect any sensors you have unplugged or jumpered, recover and weigh the refrigerant. If it is less than 2.0 lbs., recharge to bring the system up to 2.0 lbs. Clear the low refrigerant code and start the car. Turn the A/C to AUTO and let the refrigerant circulate through the system. Turn off the engine and leak check the system with an electronic leak detector to locate the source of the leak. Recover the refrigerant, repair the leak, evacuate the system with a vacuum pump for 45 minutes and recharge 2.0 lbs. of refrigerant into the system. HR-6/HT-6 compressors up through eary 2001 were belly leakers - the seals leak due to aluminum corrosion. This can be fixed but it requires disassembly of the compressor. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
soveryfaraway Posted March 24, 2012 Author Report Share Posted March 24, 2012 Let us then suppose that the system is low on refrigerant. How does it report that if the low pressure switch is disabled? Is there some other means available to sense that? The syetem uses thermisters to obtain the temperature of the refrigerant on the high side and the low side of the system. That is before and after the orifice tube respectively. If the system detects an improper condition, the ACM disables the compressor so that it will not run. This is so the compressor does not self destruct. The thermisters rarely fail. One of the most common failures is someone installs the orifice tube backward - that will damage the low side thermister and set the code for either an open or shorted low side temperature sensor. The low pressure sensor disables the compressor in the low refrigerant condition. There is also a high pressure cut off sensor that shuts the system down in the event of an overpressure condition. The proper way to diagnose and repair the system is to reconnect any sensors you have unplugged or jumpered, recover and weigh the refrigerant. If it is less than 2.0 lbs., recharge to bring the system up to 2.0 lbs. Clear the low refrigerant code and start the car. Turn the A/C to AUTO and let the refrigerant circulate through the system. Turn off the engine and leak check the system with an electronic leak detector to locate the source of the leak. Recover the refrigerant, repair the leak, evacuate the system with a vacuum pump for 45 minutes and recharge 2.0 lbs. of refrigerant into the system. HR-6/HT-6 compressors up through eary 2001 were belly leakers - the seals leak due to aluminum corrosion. This can be fixed but it requires disassembly of the compressor. So, if I understand this correctly, the B1347 code can also be created by sensing from the 2 thermistors... right? Link to comment Share on other sites More sharing options...
rockfangd Posted March 25, 2012 Report Share Posted March 25, 2012 Jumping sensor pins is not a good idea. The sensor is controlled by resistance and by jumping the pins you are changing the resistance, Therefore not enough resistance. jumping the sensor may cause a fault and cause the system to not function, or if it does function it wont for long once it realizes the resistance does not correlate. GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
soveryfaraway Posted March 25, 2012 Author Report Share Posted March 25, 2012 Never jumped a sensor. The low pressure switch, only thing jumped, is a switch - on/off. It is 1/0, not in any way a sensor. I have done 40 years+ in electronics and understand the differences. Thanks for your help. Link to comment Share on other sites More sharing options...
soveryfaraway Posted March 25, 2012 Author Report Share Posted March 25, 2012 In theory, you cannot jump a sensor. A sensor looks for a feedback in current/voltage. You CAN jump a switch (you will find examples of this in this forum), although you can debate the merits of that in each case. If you suspect a switch is defective, jumping it is safe and effective. If the problem still remains, the switch is likely not defective and you are wasting $ replacing the switch at that point. Link to comment Share on other sites More sharing options...
rockfangd Posted March 25, 2012 Report Share Posted March 25, 2012 Ok. If it were my vehicle. I would recover the system and properly charge it to 2.0lbs. and reset codes to try again. Note that if you have too much freon in the system it can be disabled also as an overpressure protection. GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
soveryfaraway Posted March 25, 2012 Author Report Share Posted March 25, 2012 Thank you... I understand the procedures for recovery as a member took time to explain above, for which I thank them much. But what I am trying to do is not just find a way to repair the AC - I am trying to gain a foothold in understanding the arcane nature that this vehicle uses to report the failures it has. I want to know every place where that error code can come from. Maybe that has to do with my background in electronics and IT. If I understand that part of it, I can live with it much better Link to comment Share on other sites More sharing options...
rockfangd Posted March 25, 2012 Report Share Posted March 25, 2012 it is pretty simple actually. The IPC keeps track of all onboard computers and displays all fault codes on the IPC. turn the key on. hold the HVAC off button and passenger temp up button for 3 seconds, once the bulb test is complete all codes will be displayed on the IPC for each system. Then once they are all shown it will prompt you on clearinng the codes, etc... GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
soveryfaraway Posted March 25, 2012 Author Report Share Posted March 25, 2012 That's quite a clue, and thank you. Getting to the codes in this SLS was a challenge, but we got there. Conflicting, but found onw that fit. I'm looking for wires at this point... connection points... the Caddy is not wireless in any way. I am looking for any wires that can yield that error code. Again, thanks! Link to comment Share on other sites More sharing options...
soveryfaraway Posted March 25, 2012 Author Report Share Posted March 25, 2012 I would state that what I am seeking is the logical mapping of the system in this area. When they designed the system, the powers that be stated that each pair of wires would connect to the central and their activities in failure would in turn create the error codes. There is a map to this. Someone knows this. You can spend hours and hours and $ and $ working on this kind of thing, but if you don't know the logic behind it, you will remain largely ignorant. Link to comment Share on other sites More sharing options...
KHE Posted March 25, 2012 Report Share Posted March 25, 2012 So, if I understand this correctly, the B1347 code can also be created by sensing from the 2 thermistors... right? Yes - here is a description of the B1347 code: If the refrigerant charge falls below 1/3 of the system capacity, the VERY LOW REFRIGERANT – A/C COMPRESSOR OFF message is displayed on the information center. The ACM determines the state of charge by monitoring the temperature change in the low side temperature sensor during the initial period of compressor engagement. The temperature drop is referenced in a table in the ACM as a function of outside air temperature. If the refrigerant charge is too low, the refrigerant boils instantaneously after it passes through the orifice tube, creating a large rapid change in the low side temp. sensor reading. If the temperature change is too great, a Very Low Refrigerant counter is incremented in the ACM. After several incidents have been counted, the ACM will set DTC B1347 and the message “VERY LOW REFRIGERANT – A/C COMPRESSOR OFF” will be displayed on the information center. The compressor clutch will disengage and remain disengaged until che B1347 code is cleared. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
soveryfaraway Posted March 26, 2012 Author Report Share Posted March 26, 2012 Thank you very much. That's exactly the info I was looking for and I appreciate your time and effort in putting it before me. My hat's definitely off to you and your knowledge. Link to comment Share on other sites More sharing options...
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