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1992 Brougham 5.7 AC diagnosis help please

4K views 10 replies 5 participants last post by  Webb92fleet 
#1 ·
Have been working on optimizing the AC on this 1992 Brougham Limo (6door). It does have a rear AC but the trouble am having is not related to the rear unit. Put a new AC Delco R4 compressor/Evaporator/Expansion Tube/ Accumulator Drier/New O-rings where system opened. Originally R-12 but switched to R134 in 2001.

Both rear and front AC system cool "OK" but am in Florida, car is black, and being a limo more windows and cabin space to cool so trying to optimize cooling ability prior to summer.

The new R-4 compressor is cycling on and off too frequently after AC has been on for 2-3 minutes. Cycles on for 5 seconds and then off for 8 seconds. Have a service information manual from GM for a Brougham which is my reference. This car, which correlates with what the manual says does not have a high pressure cut off switch. It does have a high pressure relief valve on the compressor which opens at 440PSI. It also has a low pressure cut off switch on the back of the compressor which deenergizes the clutch on the compressor for PSI reading of less than 25. It also has an Evaporator Inlet Temperature Sensor located after the expansion tube and prior to entering the evaporator. This is peculiar to the 5.7 liter. The 5.0's have what they call a Thermostatic Cycling Switch-which sounds like it does the same thing. They deenergize the clutch if evap temp is less than 0 celcius.

Using the ECC (Electronic Climate Control) features the Low Pressure Switch is not throwing a code and the ECC is not deenergizing the clutch. Both the evap inlet line and the accumulator/drier are both cold and not frosting, which from my reading indicates an adequate charge of R-134. The manifold gauge pressures are showed Low 30, High of 170 2 days ago at 70 F when initialing charging. Today at 83 F the gauges showed 50 and 280. I had two floor fans on the condenser. This car is pretty much stock so original condenser (non-parallel). The ECC is showing the evap inlet temp going below O C and that is when the clutch deenergizes. I don't have a IR thermometer so haven't been able to verify that this temp sensor is correct and would like to replace it eventually.

Anyone know where I can source this Evaporator Inlet Temp Sensor found on the 5.7's?
Am going to put a pusher electric fan on the condenser to try and get the high side pressure down. Too high on high pressure side I think?
Any suggestions on how to optimize this system. Read about the Sanden compressor-not interested! Maybe hydrocarbons like enviro-safe? Hear they create less head pressure but the compressor clutch is already deenergizing due to less than 32 F temp on evap line and that is on R-134. I assume the hydrocarbon stuff would make evap temps even lower.

Thanks in advance
 
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#2 ·
Short cycling , I have always seen from a low charge. There must be a leak somewhere. I would use a leak detector to see if I could fix the leak. I would empty the system and vac it down then measure the correct amount R-134. It will be less than the R12 that came in it . You could put gauges on it and charge it till the low side stays at 25 to 30 LBS. outside temp will change those numbers. The best way is to weigh the refrigerate then you know its right.
 
#3 ·
Personally I don't know why given the amount of R12 there is on eBay to buy people mess with the R134. Cars built for R12 using what it wasn't built for. My rant for the day... Did you use the R12 to R134 weight conversion formula to know how much R134 to use? Isn't there an expansion tube made for R134?

Anyone know where I can source this Evaporator Inlet Temp Sensor found on the 5.7's?

Do you mean the cycling switch which has a sensor attached to the inlet under the black cork tape?
 
#4 ·
Have the shop manual from GM and the short cycling, according to the onboard computer, is due to this Evap Inlet Temp Sensor. When I monitor it in real time that sensor shows a refrigerant temp going below 0 C and it correlates to the deenergizing of the clutch. After a few seconds the sensor temp goes back up to 10-11 C and the clutch kicks back in. It may be that the sensor is no longer calibrated correctly so trying to source a new one.

The onboard computer also gives the ability to monitor the low pressure cut off switch and it is not being activated so I am thinking the charge is at least enough to not trigger the low pressure cut off switch.

DB2guy-the 5.0 engines have the type of sensor you describe. The metal tail of that sensor lays along side that inlet pipe and is taped to it. It monitors the temp of the outside of that inlet pipe. The 5.7's have a port in that inlet pipe and the sensor attaches to that port so it is in direct contact with the refrigerant.

I put 90% of R134 into what was called for of R-1 of R-12of
 
#5 ·
Have the shop manual from GM and the short cycling, according to the onboard computer, is due to this Evap Inlet Temp Sensor. When I monitor it in real time that sensor shows a refrigerant temp going below 0 C and it correlates to the deenergizing of the clutch. After a few seconds the sensor temp goes back up to 10-11 C and the clutch kicks back in. It may be that the sensor is no longer calibrated correctly so trying to source a new one.

The onboard computer also gives the ability to monitor the low pressure cut off switch and it is not being activated so I am thinking the charge is at least enough to not trigger the low pressure cut off switch.

DB2guy-the 5.0 engines have the type of sensor you describe. The metal tail of that sensor lays along side that inlet pipe and is taped to it. It monitors the temp of the outside of that inlet pipe. The 5.7's have a port in that inlet pipe and the sensor attaches to that port so it is in direct contact with the refrigerant.

I put 90% of R134 into what was called for of R-1 of R-12of
 
#7 ·
Here is a thread on the same topic.


I don't know if this is it or not or if they even have it.
Sounds like one of those rare vintage parts.

Salvage yard search for a yard who has the same car is what you will probably have to do.
.
 
#10 ·
Refrigerent pressure & tempiture are directly related.
R-134a Temp Chart

At 28 PSI on the low side the temp would be 32 F / 0 C, your cutout temp.
50 psi is 54 F.

Was the compressor cycling off at the same time the low side read 50 psi?

Perhaps the oriface tube replaced is not the correct size, too small.
There should also be an oriface in the rear unit.

Is both the front & back blowing about the same temp?

Was there metal from the old compressor that might be in the remaining componants?

Was the system evacuated under a vacuum for a while?
 
#11 ·
Have been working on optimizing the AC on this 1992 Brougham Limo (6door). It does have a rear AC but the trouble am having is not related to the rear unit. Put a new AC Delco R4 compressor/Evaporator/Expansion Tube/ Accumulator Drier/New O-rings where system opened. Originally R-12 but switched to R134 in 2001.

Both rear and front AC system cool "OK" but am in Florida, car is black, and being a limo more windows and cabin space to cool so trying to optimize cooling ability prior to summer.

The new R-4 compressor is cycling on and off too frequently after AC has been on for 2-3 minutes. Cycles on for 5 seconds and then off for 8 seconds. Have a service information manual from GM for a Brougham which is my reference. This car, which correlates with what the manual says does not have a high pressure cut off switch. It does have a high pressure relief valve on the compressor which opens at 440PSI. It also has a low pressure cut off switch on the back of the compressor which deenergizes the clutch on the compressor for PSI reading of less than 25. It also has an Evaporator Inlet Temperature Sensor located after the expansion tube and prior to entering the evaporator. This is peculiar to the 5.7 liter. The 5.0's have what they call a Thermostatic Cycling Switch-which sounds like it does the same thing. They deenergize the clutch if evap temp is less than 0 celcius.

Using the ECC (Electronic Climate Control) features the Low Pressure Switch is not throwing a code and the ECC is not deenergizing the clutch. Both the evap inlet line and the accumulator/drier are both cold and not frosting, which from my reading indicates an adequate charge of R-134. The manifold gauge pressures are showed Low 30, High of 170 2 days ago at 70 F when initialing charging. Today at 83 F the gauges showed 50 and 280. I had two floor fans on the condenser. This car is pretty much stock so original condenser (non-parallel). The ECC is showing the evap inlet temp going below O C and that is when the clutch deenergizes. I don't have a IR thermometer so haven't been able to verify that this temp sensor is correct and would like to replace it eventually.

Anyone know where I can source this Evaporator Inlet Temp Sensor found on the 5.7's?
Am going to put a pusher electric fan on the condenser to try and get the high side pressure down. Too high on high pressure side I think?
Any suggestions on how to optimize this system. Read about the Sanden compressor-not interested! Maybe hydrocarbons like enviro-safe? Hear they create less head pressure but the compressor clutch is already deenergizing due to less than 32 F temp on evap line and that is on R-134. I assume the hydrocarbon stuff would make evap temps even lower.

Thanks in advance
Hey new here did you ever find that inlet temperature sensor for the 5.7 having the same problem i would love help. Thanks
 
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