QuestionQUESTION: Tom, you have stated "Expert: Tom Joy
Date: 6/5/2007 Converting from R-12 to R-134 freon causes numerous problems with the sensors as they are not calibrated for the R-134 freon."
My '89Eldo has Lo-side-Press. Sender, Lo-side-temp. and Hi-side-temp. senders. Using multimeter (volt/ohm/temp.K-termocouple)) how to check these senders and what they are sending? After over-night parking, my Eldorado BCM-Data shows 1degC differenc between Lo & Hi temp. senders and 5degC between Outside temp. sender. Also, BCM-input shows A/C HI pressure.
ANSWER: Just about every one that is converted keeps sending a low refrigerant pressure display and or CODE and shuts off the compressor.
If you want to try it, Go ahead.
---------- FOLLOW-UP ----------
QUESTION: Thank you Tom for reply.
My 1989 Eldorado is one of them and it seems that my AC-senders are working properly however, the information that computer receives is not matching stored data.
Tom (to be sure that they are ok) where to find how these three senders work?
And how to tell if they are broken or are not sending proper information?
ANSWER: I do NOT understand this statement : the information that computer receives is not matching stored data.
The sensors work on refrigerant pressures.
---------- FOLLOW-UP ----------
QUESTION: Tom, the following is just an observation.
My 1978 Eldorado A/C has only one pressure sensor and that system works very well on R134a.
My 1989 Eldorado has onboard computer (BCM) reading sensors’ input and more likely comparing it to the stored data in its memory (ROM).
The ’89 Eldorado A/C system in addition to the computer operates with help of three sensors on the refrigerant lines (lo side pressure, lo side temp. and hi side temp.) and also takes into account outside and inside car temperatures.
I think that loside pressure sensor is just an on-off switch and it does not provide actual pressures in the lines as a function RPM. I think it works the same as 1978 Eldorado. The temperature sensors are not thermocouples thus more likely are thermistors.
R12, R134a or hydrocarbons have different temperature versus pressure relationships. At high AC compressor pressures there is a significant difference between these refrigerants. Since R134a did not escape thus more likely hi side temperature sensor data does not match R12 information stored in the BCM Read Only Memory or it could be that computer uses lo-side temperature for comparison.
Temperature sender if it is thermistor at high-pressure location and temperature has low resistance. Thermistor at lo-pressure location and low temperature has high resistance. So maybe it is possible to fool the computer by adding in line resistor to compensate for different press. Vs temperature curves of R12 & R134a, provided sensors are working properly.
AnswerThat is one way that you can ALTER the system. I do NOT encourage altering the systems as when you are doing diagnostics with the scanner and or on-board computer display the data from the sensor will NOT match the factory specs and can lead to false readings. If you ALTER the system, Put a small white tag on the hose describing what you did and seal your writing with plastic tape so the next tech who runs a scan of the system will be able to read your ALTERATION.
