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George H.
George H., ASE Certified Technician
Category: Cadillac
Satisfied Customers: 18394
Experience:  ASE Master Tech 15+ Years
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Cadillac Deville: i have a 97 deville 4.6. repalced compressor

Customer Question

i have a 97 deville 4.6. repalced compressor with dryer and orifice tube, flushed lines. Low pressure switch and recharged, pump cycles off too quickly. At 35 Psi on low side it turns pump off for 30 seconds. No climate control codes at this time
Submitted: 1 year ago.
Category: Cadillac
Expert:  George H. replied 1 year ago.
Hello I will help you with your question, What happens if you bypass the low pressure switches? How cold does it get and where does the low pressure go?
Customer: replied 1 year ago.
If I bypass low pressure switch no change occurs. If I short out connector on high side no change occurs. Should i short them both out simultaneously?
Customer: replied 1 year ago.
Once low pressure hits 30 or 35 psi compressor shuts off for 30 seconds. High side will be at approx. 185 when compressor shuts off.
Expert:  George H. replied 1 year ago.
No change? So the compressor still cycles off for 30 seconds after the low pressure reaches 35 psi? What is the high side pressure during this time?
Customer: replied 1 year ago.
If I jump the relay, system does not cycle and pressures are 35 and 185 approximately. AC blows cold.
Expert:  George H. replied 1 year ago.
OK, but I am trying to see what is turning off the compressor relay. Can you see if the ground that turns the relay on goes away when the compressor shuts off? Do you have a scantool that will show you the relay control in the PCM?
Customer: replied 1 year ago.
Yes but is the inadvert relay the compressor relay on this car? What do I watch for on scan data?
Expert:  George H. replied 1 year ago.
In the PCM data there should be a PID for the A/C relay. See if it is turning off when the compressor kicks out, if it is look at the A/C request and see if that is changing to NO. If it is then the programmer that gets the signal from the pressure switches is sending bad data. Keep the sensors bypassed while you are looking at the scandata so you know they are not sending low or high pressure signals to the programmer. The AC relay is the one you jumper to keep the compressor on. You know what pins are for the compressor, on the other two one will have 12 volts, the last one is what the PCM uses to turn on the relay by grounding it. You put a meter to the positive side of the battery or fuse block and use the other lead to see if the ground is going away. If you see 12 volts you have ground, if it is near 0 volts then you don't have a ground. Let me know what you find and how I can help Thank you
Customer: replied 1 year ago.
I only have the high side pressure switch bypassed at the moment, is that ok for this test you want me to conduct?
Expert:  George H. replied 1 year ago.
No, the switches are in series so you need to bypass both of them. They provide 12 volts to the control side of the relay and the PCM provides the ground. As the compressor comes back on after 30 seconds I think the power side is fine, it is the PCM turing it off by losing the ground. Let me know Thank you
Customer: replied 1 year ago.
I shorted both switches and now there is no compressor operation. LOW REFRIGERANT AND AC COMPRESSOR OFF messages are displayed in IPC. Scan data shows 2 relays cycling ON and OFF before all of this every 13 seconds equally as clutch would shut on and off
Expert:  George H. replied 1 year ago.
Is this new? Did you clear the codes after the switches are bypassed? Before you bypassed the switches and there was no change. Be sure to keep whatever you are using to bypass the switch away from metal, if oyu don't have 12 volts at the switch connector change the cruise fuse. The codes have to be cleared to let the compressor turn on so if you have the key on and unplug a switch that will set a code. Let me know Thanks
Expert:  George H. replied 1 year ago.
Looks like they lost my answer , Bypass the switches with the key off, clear the codes and then it should work. If you have a code set the compressor will not be turned on
Customer: replied 1 year ago.
Cleared codes manually thru IPC. Shorted both switches, no change occurs. Cycling every 10-13 seconds on and off. Relays 1 and 2 show ON/OFF as this happens on scan data
Expert:  George H. replied 1 year ago.
But now the compressor turns on now right? Go ahead and check the relay for ground and the scan data for A/c relay and request state.
Customer: replied 1 year ago.
Yes compressor runs. Clutch cycles on and off. Both scan data items shows AC relay on and off every 10-13 seconds.
Expert:  George H. replied 1 year ago.
OK, can you see the A/C request? Is it turning from YES to NO?
Customer: replied 1 year ago.
Yes, i have solus ultra, scan data shows ON and OFF relays 1 and 2 every 10-13 seconds. Does not display yes or no
Expert:  George H. replied 1 year ago.
I don't know what relays 1 and 2 are, the AC compressor only has one relay. There should be a PID for the request to turn on the relay from the programmer, Snappy might call it something else, I only know what it looks like on a Tech 2. That is what you need to see, if it is changing then you will need to check at the programmer to see if the inputs are steady or if it is responding to an input that makes it think it is not safe to run the compressor. The switches should open at 10 psi and 430 psi so I doubt it is that. Does this car have digital or analog gauges?
Customer: replied 1 year ago.
Digital gauges, coincidentally we did replace or have the IPC cluster rebuilt due to illumination and gauge function problem a year or two ago
Customer: replied 1 year ago.
However the electrical diagram shows the relay's ground control lie within the PCM
Expert:  George H. replied 1 year ago.
That may be the problem then. The digital stuff is failing at a high rate. You are going to have to check the inputs at the programmer and see if the temperature sensors are holding at 2.5 volts as the system runs, if they get too close to 5 volts or too close to 0 volts the system will shut off the compressor. A lot goes into the decision to turn on the compressor so with any electronic controller there is no way to test directly you have to check all the inputs and see if the output makes sense, if it does not you replace the controller. Let m eknow if you can see the AC request from the programmer to the PCM, if you can we can move onto testing the programmer inputs.
Customer: replied 1 year ago.
the compressor relay ground is lost as the clutch cycles on and off. when we lose it we have 12 volts, this i assume is not normal. we are unable to test beyond that. ideally we want that ground to remain for longer and return quicker correct? What are the dangers of jumping the relay and have no clutch cycling for the moment. pressures maintain 30 on low side 200 on high side, ambient temp is 90 F. Scan data is limited on this, what would be your best guess given the info thus far?
Expert:  George H. replied 1 year ago.
The compressor is grounded by the PCM it is turning it off in response to something. If you can see the request is changing to NO or OFF then you know it is coming through the serial data link from the programmer. I think it is the programmer but it is an expensive guess if I am wrong. The digital dash switch might be telling the programmer to turn off the AC. If the inputs to the programmer check out I would replace it but you have the two pressure sensors, two refrigerant temperature sensors, the ambient temperature sensor and the cabin temperature sensor all of which have the ability to cause the programmer to turn off the compressor and that might let them cool, heat or change enough that it turns the input back to OK and the programmer turns the system back on. Let m eknow if you want to take a guess or go through testing the inputs at the programmer under the dash. Thank you
Customer: replied 1 year ago.
Life is just getting better with this car. Now there is no power to compressor at all. Reoccuring IPC LOW REFRIGERANT COMPRESOR OFF message. Codes cleared, system is full but no compressor activity. Relay swapped and digital display acknowledges command but no clutch engagement. Great.
Expert:  George H. replied 1 year ago.
If the fault is present when you first turn on the key you will get a fault and the compressor will be disabled. Can you pull codes with the HVAC controls and see if something is there? Your solus may not be up to the job here.
Customer: replied 1 year ago.
Your'e right, limited information. I do get the message first thing after turning engine on. Is it possible for blower motor to have an effect on any of this? We just replaced it yesterday. Aftermarket of course.
Expert:  George H. replied 1 year ago.
The blower should not affect compressor operation, it does work?
Customer: replied 1 year ago.
Yes blower works. But now i cant get compressor to come on at all despite full charge. Get the IPC cluster codes right away. Jumping both pressure switches does nothing and scan data shows no relay activity.
Expert:  George H. replied 1 year ago.
There are a couple more things that can keep it from coming on, high coolant temp would do it or you could just have a failed programmer. The programmer does signal the blower to run. When you were having it cycle before did the cooling fans turn on and off with the compressor?
Customer: replied 1 year ago.
Gonna call it a day, hope you can help tomorrow, if not Monday.
Customer: replied 1 year ago.
Yes cooling fans did cycle with compressor. I did notice inputs from cluster (programmer?) did not match scan data. As far as on or off . I tried the rear defrost, recirc function etc. All inconsistent. They lit up on the dash but scan data showed they were off.
Expert:  George H. replied 1 year ago.
I plan on being here tomorrow Check to see if you blew the cruise fuse, if you don't have 12 volts at the switches or at two of the pins on the compressor relay then you need to check the fuses.https://dl.dropboxusercontent.com/u/26725849/compressor.pdf Let me know how I can help Thank you
Customer: replied 1 year ago.
Hello George , we are continuing with the cadillac AC problem, If we jump the relay the compressor comes on but now we dont have cooling fans. High pressure will skyrocket so we must pull the jumper wire. Immediately we get the IPC message of LOW REFRIGERANT AND AC COMP OFF
Expert:  George H. replied 1 year ago.
If you are turning the compressor on by jumping the relay then the computer does not know the compressor is on so it does not turn on the fans. It sounds like the computer is not seeing the a.c. request from the controls so you are at the same place. Have you installed working controls?
Customer: replied 1 year ago.
No, have not tried anything since we last talked. All fuses ok, even the junction box in trunk
Expert:  George H. replied 1 year ago.
Ok, you have changing results and known digital controls that fail. The PCM gets a signal from the programmer that the compressor is requested to be on and in return it turns on the cooling fans.
You can try turning on the fans by jumping the relay then turning on the compressor and seeing if the pressure still goes sky high, if it does then you have a blockage in the condenser or the O tube and those pars along with the compressor will need to be replaced and the system flushed clean of the metal.
Let me know how I can help
Thank you