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Grand National A/C issues

Tims87gn on Sat June 12, 2010 9:41 AM User is offline

Year: 1987
Make: Buick
Model: Grand National
Engine Size: 3.8 tur
Refrigerant Type: 134a conver
Ambient Temp: 88
Pressure Low: 35
Pressure High: 250
Country of Origin: United States

I decided to get my a/c operational again after being down with a compressor failure for 5 years. My orifice tube was covered with garbage so I knew the entire system needed cleaning. I removed every component and flushed them numerous times until I got no debris coming out. I reassembled with new compressor, accumulator, orifice tube, seals everywhere and added 8oz of ester oil prior to starting the system. I cycled the compressor by hand at least 10 revolutions to circulate to new oil. I drew the system down to 30" Hg for and hour and let it sit overnight. It held perfectly. the next day it was 88*F and I began adding 134a after jumpering the pressure switch. Each time I added a can, I was careful to purge the lines of air before adding the freon. Around can #3 the line after the orifice tube going into the evaporator began frosting heavily. I gave up not long after with the low side at 35 and high at 250. At no time did I every start seeing a hint of cold air out the dash vents. They remained at a constant 100* the entire time. I am going to review the factory manuals today to understand how the ducts and passages are actuated, but I'm feeling like my issue is at the orifice tube. Would a blockage completely prevent any cold air from coming out the vents?? Any insight is appreciated.

Thanks, Tim

GM Tech on Sat June 12, 2010 10:09 AM User is offline

Was evaporator flushed while still in car? If so, how do you know the flushing agent is completely out of it?

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......

Tims87gn on Sat June 12, 2010 10:48 AM User is offline

The evaporator was removed from the car and flushed multiple times until particles were gone, then blown out with compressed air.

HECAT on Sat June 12, 2010 2:41 PM User is offline

Your pressures do not indicate OT blockage, they look good. I think it is in the blend door and or heater controls. You can block off (pinch off w/ vice grips) one of the heater hoses and see if vent temps drop.


HECAT: You support the Forum when you consider for your a/c parts.


Tims87gn on Sat June 12, 2010 4:17 PM User is offline

Tims87gn on Sat June 12, 2010 4:25 PM User is offline

I was surprised today driving the car home from a car show. It was 91*F outside and pretty hot in the car, I had the windows down and wanted to get some air thru the vents. For the heck of it I selected Normal AC. I was astonished when cold air started coming out the vents! It actually read 70* at the vent. I didn't run it long since I knew I didn't have a full charge of 134a. So why did I not get ANY cold air the other day and now I have working a/c? BTW, they was no frosting of the line after the orifice tube today.


HECAT on Sat June 12, 2010 4:35 PM User is offline

Better air flow over the factory tube and fin condenser.


HECAT: You support the Forum when you consider for your a/c parts.


nighthawk4603 on Sat June 12, 2010 7:14 PM User is offline

? what did you use to flush your system? I have a locked up comp that I am considering DIY but don't have a flush system

Tims87gn on Sat June 12, 2010 10:39 PM User is offline

I continued to add freon to the system and drove the car again. At 92*F I got 36 on the low side and 260 on the high side. My vent temps got down to 40* while driving. I was certainly comfortable and an improvement, but I am hoping I can get it lower. At this point, I have added about three cans total of 134a. What if any cautions should I be concerned with at this point? Where is a safe stopping point as far as adding freon?

Dougflas on Sun June 13, 2010 12:15 AM User is offline

a safe stopping point is to measure the in and out tubes of the evap. Should be close to the samr temps.

fonebone on Sun June 13, 2010 9:57 PM User is offline

Hi Tim; For a car that was converted, those(40 degree) temps @92 ambient outside air are incredible! My advice(and others here I'm sure will agree) enjoy it as is, don't push it further,you have done well!!

Edited: Sun June 13, 2010 at 9:58 PM by fonebone

JACK ADAMS on Mon June 14, 2010 12:33 PM User is offline

This is a “G” body car and has two vacuum lines the feed into the cab of the car. One is a grey or black for main vacuum and the other may appear to be a pink that feeds to the hot water shut off valve. Make sure that these are in good working order, Also since you did a 134a conversion did you switch or adjust the low pressure cycling switch? The OEM condenser is a 10mm tube-n-fin style that will need extra cooling by adding an electric fan or changing to a PFC.

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