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JHoop, Cadillac Technician
Category: Cadillac
Satisfied Customers: 5446
Experience:  14 Year Engine Builder,16 years as a Tech HvyLine, Suspension, Electrical, Brakes, 6 Year Shop Owner
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Cadillac Deville: I have a 1999 Cadilac Deville. The "low

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I have a 1999 Cadilac Deville. The "low refrigerant " reading came on and it said a/c off. I checked the a/c under the hood and the compressor is not coming on. I checked the fuses and they are ok. I'm getting about 100psi on the gauges with the compressor not running. The owners manual says it could be a defective sensor. What should I look for ?
Hello,I will be glad to try and assist you with this,Welcome to Just Answer.


The AC low pressure switch will cut off the compressor operation and cause this problem here when it detects the ac pressure at or below 10 psi.If you are above this pressure here then most likely the freon levels are ok and you may just have a faulty switch.

To be safe though it may be worth evacuating the freon and then recharging the freon,clear out the failure codes in the computer systems and then see if it operates normally then,if it does then you should be good to go except the system most likely has a small freon leak that needs located and repaired.

If the problem is still present then most likely the low pressure switch is faulty and needs replaced.

This switch is located on the ac line near the firewall on the passenger side just above the ignition coils.

Let me know if you need anything else,click accept if you feel satisfied with your answer as this is how I get credited for my time,Thanks Pete!
Customer: replied 6 years ago.
I have checked the low pressure switch, and i think it is ok. I jumpered the lps with a paper clip with no results. The compressor still refuses to run. I am an HVAC tech and have been in the residential hvac business for 35 years, but have no experience with autos or r-134a. What other remities do you suggest? I also reset the service indicator (low refrigerant, a/c off) but it comes back on.
Have you removed and refilled the freon in the vehicle to see if it was low?

Let me know,Thanks Pete!
Customer: replied 6 years ago.
Pete, I have not removed the freon. My guages read near 100 psi. With the low pressure switch jumpered, the compressor should start, right??? When I reset the "low refrigerant " I just held down the reset button on the instrument panel. Is that the correct way to reset it??
Your vehicle may have codes stored in the computer systems that are related to this problem here and on allot of vehicles when a code sets in a system it will disable that system from operating and this may be why it isn't engaging here.

You will have to have someone with a code reader or scan tool clear out the fault codes to see if it operates normally then,usually resetting it the way you had done here wont reset the system.

Thanks Pete!
Customer: replied 6 years ago.
Pete, I have a code reader, and have already reset the codes. There were no codes related to the a/c problem. The only code that was displayed was p0503 "speed sensor intermittant/high input" which is another different problem that my wife has reported as the car stalls with no warning. This car only has 74K miles and runs well, beside the above mentioned problems. There is one other code, p1660, defined as "undefined code" but both codes have been reset. The car has not been driven sense the codes have been reset. What now???
I apologize as I will have to opt out of this question as I don't know what the next check/step will be here to locate the source of this failure.I will put this question back on the list for all experts to see if they can help.

You wont be charged again for this.Don't respond to me as it will keep the question locked to me and other experts wont be able to see it.

Thanks Pete!
Customer: replied 6 years ago.
Relist: Other.
Pete, the expert said he would opt-out and put my problem back on the board. I'm waiting for another experts advice.
Customer: replied 6 years ago.
I'm still waiting to be connected to another expert!!! Pete, you said you would put my question back on the board for another expert to contact me and help with my problem. This is day two. No contact yet. What am I doing wrong???? Thanks. Phillip
Hello , my name is XXXXX XXXXX thank you for choosing Please tell me all the problem as my answers are based on the information you provide.

Keep the lo switch jumpered and clear the a/c codes. Remove the battery cable and touch it to another. Replace the cable. Start the engine. If the compressor does not kick on there is a code that is overlooked or an electrical issue such as a fuse or relay.

If you have any more questions or need diagrams or service info, please don't hesisitate to ask If this answer helped you, please click ACCEPT.

Your question is always open and you can get back to me at any time by answering any e-mail related to this question or by simply logging on to your JA account and go to your questions. God Bless

Please leave positive feedback. As you can see I have excellent ratings in all my categories. Also remember I am not at the vehicle, Please don't leave a negative report. Thanks again, JHoop
Customer: replied 6 years ago.
JHoop, Thank you for your response. I've tried everything you suggested except disconnecting the battery cables to reset the computer. It would be helpfull to me if you could send me a schematic diagram, as I am a qualified electrician and will be able to trouble-shoot with the help of a wiring diagram. I'm going now to try the battery disconnect. Thanks, Phillip
Let me know if the battery disconnect does not work. I have all the diagrams.
Customer: replied 6 years ago.
JHoop, The battery disconnect did work!!!! I wasn't resetting the computer codes correctly.. I have a code reader and I reset the codes on it but it did not reset the low refrigerate code. Now can you tell me where is the speed sensor. My wife has experienced the car stalling while driving and the code reader says "intermittant speed sensor". Where is it???? Thanks, Phillip
You were resetting the codes correctley as I know this from my GM training.

Thye speed sensor is located on the top of the passenger side transaxle near tha e mount.graphic
Customer: replied 6 years ago.
Thank you !!! I would never have been able to find it without your input.. One last thing before We conclude; can you send me the wiring diagram for future use??? Thanks again, Phillip
Of the A/c system?
CLICK HERE for that diagram. Please accept my expertise as it has helped you. Bonuses are welcome, JHoop
JHoop, Cadillac Technician
Category: Cadillac
Satisfied Customers: 5446
Experience: 14 Year Engine Builder,16 years as a Tech HvyLine, Suspension, Electrical, Brakes, 6 Year Shop Owner
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