Automotive Air Conditioning Information Forum (Archives)

Provided by www.ACkits.com

We've updated our forums!
Click here to visit the new forum

Archive Home

Search Auto AC Forum Archives

compressor cycling: cadillac

joe_mn on Mon July 14, 2008 10:20 PM User is offline

Year: 1996
Make: seville
Model: sts
Ambient Temp: 90
Pressure High: 240

i changed out my compressor and it seems to work ok but i have noticed it cycles on/off a bit. i can feel the clutch kick in and the motor thumps a bit. i believe caddy changed the a/c mounting in 2k or so to improve rigidity. maybe its just a caddy thing. the vent temp seems to feel good but when the compressor cycles on, the temp drops. on/off, cool to colder. does this sound like low charge? should a 96 compressor cycle very little? its been 90 or so lately and the air does work ok. rad fan runs at medium speed with high side at 220. than pressure rises to 245 and fans turn on high. than pressure drops and fans go back to medium speed.

GM Tech on Tue July 15, 2008 7:57 AM User is offline

Sounds like it is working as it should.. The Caddy system has an excellent low refrigerant, and very low refrigerant detection mechanisms- so you need not worry about harming your compressor, the car knows when to shut it down and warn you with the messages. Most wait until that happens to post here. Compressor cycling is NOT done by pressure as most vehicles- rather by thermistor values- one on the high side and one on the low side- and if either of those go bad, you will be the first to know. So the car is very smart and is doing what it is designed to do..

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

joe_mn on Tue July 15, 2008 1:23 PM User is offline

i know i am slightly low on charge. tag says 2lbs and i am at 27oz. after i replaced my low side thermistor, i just decided to only add 24oz. i ran it for several days and than added a few more oz. i am still waiting for it to stop working. maybe i am cynical. i never really drove the car the last 8yrs we have owned it. wifes car. i had the motor out last summer and did not drive it after i fixed it. i finally replaced the bum compressor but i did not change the condenser so i had little faith it was going to work. i do like it though. its in great shape.

JJM on Wed July 16, 2008 2:53 AM User is offline

Quote
The Caddy system has an excellent low refrigerant, and very low refrigerant detection mechanisms

I wonder if that still applies to late model Caddy's... because the compressor on my '05 DTS never shut down (from a large discharge line leak) until the system was completely empty - around 30 PSI static. And the "SERVICE AC SYSTEM" message never displayed either, which was typical when these systems would run even slightly low.

'05 Caddy DTS Compressor Did Not Shut Down

I was sure the new sensor included with the new discharge line would do the trick. But even with an empty system, no codes and no "SERVICE AC SYSTEM" message. Didn't need to clear codes to get the compressor to kick back on either; as the charge was being weighed in, the compressor engaged about 1/4 of the way through. Lovely.

Only way I get the "SERVICE AC SYSTEM" message and a code was by disconnecting the sensor (new and old one).

Perhaps the Mitsubishi scroll is so hearty, low refrigerant and oil doesn't affect it, hence a change in programming. After running my system low for so long, I was expecting to OT to show bad news, but it was surprisingly clean.

Joe

When considering your next auto A/C purchase, please consider the site that supports you: www.ACKits.com


GM Tech on Wed July 16, 2008 8:17 AM User is offline

Things did change slightly when the Caddy went to the Mitsubishi system here are some tidbits from the '05 service manual

A/C Refrigerant Low Temperature Sensor
The dash integration module (DIM) monitors the sensor to determine low side pressure based on the pressure to temperature relationship of the R134a. This sensor is located on the low side line. The sensor is used to cycle the A/C compressor ON and OFF to prevent the evaporator core from freezing. A thermistor inside the sensor varies its resistance to monitor the temperature of the Freon. The DIM monitors the voltage drop across the thermistor when supplied with a 5-volt reference signal. The DIM will send a class 2 message to the PCM to stop requesting the A/C compressor clutch operation if the temperature drops below 2°C (28°F). Vehicles operating above 32 km/h (20 mph) will be controlled to a minimum ON time of 46 seconds before the DIM will allow the clutch to disengage. The sensor must be above 10°C (50°F) before the DIM will request A/C compressor clutch operation again.

The sensor operates within a temperature range between -40°C (-40°F) to 215°C (-355°F). If the DIM detects an open in the A/C refrigerant low temperature sensor or circuit, the class 2 message sent to the PCM will not allow A/C operation. The HVAC control module (IPM) will then send a request to the Radio for display of the "SERVICE A/C SYSTEM" that will be displayed on the DIC. The HVAC control module (IPM) will also display A/C OFF on the module as long as the condition is present.

A/C Refrigerant Pressure Sensor
The A/C refrigerant pressure sensor is a 3-wire piezoelectric pressure transducer. A 5 volt reference, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0-5 volts. . When the A/C refrigerant pressure is low, the signal value is near 0 volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts.

The A/C refrigerant pressure sensor prevents the A/C system from operating when an excessively high or low pressure condition exists. The PCM disables the compressor clutch under the following conditions:

• A/C pressure is more than 2850 kPa (413 psi). The clutch will be enabled after the pressure decreases to less than 1750 kPa (254 psi).

• A/C pressure is less than 204 kPa (30 psi). The clutch will be enabled after the pressure increases to more than 220 kPa (32 psi).

If the PCM detects a failure in the A/C refrigerant pressure sensor or circuit, the class 2 message sent to the HVAC control module (IPM) will be invalid. The HVAC control module (IPM) will then send a request to the Radio for display of the "SERVICE A/C SYSTEM" that will be displayed on the DIC. The HVAC control module will also display A/C OFF on the module as long as the condition is present.



-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Back to Automotive Air Conditioning Forum

We've updated our forums!
Click here to visit the new forum

Archive Home

Copyright © 2016 Arizona Mobile Air Inc.