| A/C pressures [message #312806] |
Sat, 04 February 2017 16:53  |
Dan Gibb
Messages: 24
Registered: May 2015
Location: Tucson, Arizona
Karma: 0
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Junior Member |
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Good Afternoon everyone,
Does anyone know what the idle A/C LOW side pressure should be? I am using a Duracool equivalent.
At an ambient temperature of 75, I am showing 40 lbs on the LOW side. and a 60 degree temp from my vents.
On the road at 2000 rpm I am showing a temperature at the vents of 51 degrees.
Do I need to add some more or take some out?
Dan Gibb
1977 Eleganza II
Tucson, Az
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| Re: A/C pressures [message #312810 is a reply to message #312806] |
Sat, 04 February 2017 18:14  |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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Senior Member |
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I believe that 2.5 to 3 cans of Duracool is correct.
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: A/C pressures [message #312813 is a reply to message #312806] |
Sat, 04 February 2017 19:08 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Senior Member |
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Sir the 77-78 ac holds more Freon than the earlier models. The 77-78 supplement manual has a good write up on pressures and temps.
Dan Gibb wrote on Sat, 04 February 2017 17:53Good Afternoon everyone,
Does anyone know what the idle A/C LOW side pressure should be? I am using a Duracool equivalent.
At an ambient temperature of 75, I am showing 40 lbs on the LOW side. and a 60 degree temp from my vents.
On the road at 2000 rpm I am showing a temperature at the vents of 51 degrees.
Do I need to add some more or take some out?
C. Boyd
76 Crestmont
East Tennessee
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| Re: A/C pressures [message #312814 is a reply to message #312813] |
Sat, 04 February 2017 19:30 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Senior Member |
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sir the 77-78 has a different type bypass expansion valve that cycles the compressor and needs a little more operating time to stabilize pressures and temps. There is a lot of info in the 77-78 supplement that is not in the older manuals.
C Boyd wrote on Sat, 04 February 2017 20:08Sir the 77-78 ac holds more Freon than the earlier models. The 77-78 supplement manual has a good write up on pressures and temps.
Dan Gibb wrote on Sat, 04 February 2017 17:53Good Afternoon everyone,
Does anyone know what the idle A/C LOW side pressure should be? I am using a Duracool equivalent.
At an ambient temperature of 75, I am showing 40 lbs on the LOW side. and a 60 degree temp from my vents.
On the road at 2000 rpm I am showing a temperature at the vents of 51 degrees.
Do I need to add some more or take some out?
C. Boyd
76 Crestmont
East Tennessee
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| Re: [GMCnet] A/C pressures [message #312817 is a reply to message #312806] |
Sat, 04 February 2017 20:08 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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It will take just under 3 cans. After you have the second can in run the air conditioner on high, run the engine at 1500 rpm and fill from the third can until the low side pressure is about 20 to 22 psi. At higher ambient temperatures (above 90) you fill to a little higher pressure.
40 psi at 1500 rpm means you have it too full. If you drain some out to lower the psi it will get much colder. If you have too little it will get so cold that the evaporator will freeze the moisture in the air and block the evaporator so that it will block the airflow.
In very humid areas you may need more than 22 psi to prevent freeze up. You can always add a bit more if this becomes a problem.
Emery Stora
77 Kingsley
Frederick, CO
> On Feb 4, 2017, at 3:53 PM, Dan Gibb wrote:
>
> I
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