Home » Public Forums » GMCnet » some closure on my AC system (I think it is actually working)
| some closure on my AC system [message #138367] |
Wed, 10 August 2011 22:35  |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Senior Member |
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I did some more testing today.
It was in the mid 70's so more normal pressures.
I knew the main evap was clean and I had the front off
I had my shiny and clean harbor freight A/C gauges hooked up
Engine running at 1500 RPM scaring women and small children.
I turned on the fans on the dash air and the secondary AC fan was OFF.
I added Duracool to get 20 PSI and the high side was 125-130.
Ran for about 10 minutes and it looked stable.
The evap was dripping and the low side was COLD.
I then turned on the secondary fan on high ( this thing has some serious airflow)
The discharge air on the secondary started out cold, but soon warmed up Hmmmm
The low side climbed to 25-28 and the high side dropped to 110-115
So it looks like the compressor can't keep up with both units running full blast.
Maybe at freeway speeds (2500RPM) it could, but not at 1500 rpm with no air flow through the radiator!
So I think with a large secondary evap, it's possible to overwhelm the compressor.
I still think the compressor is weak.
Now to get airflow through the dash vents...
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: [GMCnet] some closure on my AC system [message #138369 is a reply to message #138367] |
Wed, 10 August 2011 22:46  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Keith,
An up-to-spec A-6 compressor should produce 42,800 BTU at 4000 (compressor)
rpm -- I don't know the other specs, but probably a standard day of about
70*F.
Ken H.
On Wed, Aug 10, 2011 at 11:36 PM, Keith V <my427v8@hotmail.com> wrote:
>
>
> So it looks like the compressor can't keep up with both units running full
> blast.
>
> Maybe at freeway speeds (2500RPM) it could, but not at 1500 rpm with no air
> flow through the radiator!
>
> So I think with a large secondary evap, it's possible to overwhelm the
> compressor.
>
> I still think the compressor is weak.
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: some closure on my AC system [message #138469 is a reply to message #138367] |
Thu, 11 August 2011 13:26 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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| Keith V wrote on Wed, 10 August 2011 23:35 |
I did some more testing today.
It was in the mid 70's so more normal pressures.
I knew the main evap was clean and I had the front off
I had my shiny and clean harbor freight A/C gauges hooked up
Engine running at 1500 RPM scaring women and small children.
I turned on the fans on the dash air and the secondary AC fan was OFF.
I added Duracool to get 20 PSI and the high side was 125-130.
Ran for about 10 minutes and it looked stable.
The evap was dripping and the low side was COLD.
I then turned on the secondary fan on high ( this thing has some serious airflow)
The discharge air on the secondary started out cold, but soon warmed up Hmmmm
The low side climbed to 25-28 and the high side dropped to 110-115
So it looks like the compressor can't keep up with both units running full blast.
Maybe at freeway speeds (2500RPM) it could, but not at 1500 rpm with no air flow through the radiator!
So I think with a large secondary evap, it's possible to overwhelm the compressor.
I still think the compressor is weak.
Now to get airflow through the dash vents...
|
Keith: I hate to keep harping on "sweating back to the compressor" thingie, but...... It ain`t no trouble to pull the right inner fender liner, about 3 minutes with a 3/8 socket, and look and see if the low pressure line is sweating at the compressor, 1500 rpm with a shop fan blowing on the grill. If not sweating add a little gas til it does then see what the AC vent temp and gauges say. Just from my experience with big trucks. I have no formal AC training and I do not know what the gauges actually do, I just use them to switch from a vacuum pump to gas. If the syatem will hold a vacuum it will hold freon, if the compressor runs and the low pressure line is sweating at the compressor and the high pressure line is to hot to touch you will have cold AC. If you cannot get the line to sweat at the compressor after adding gas then you have a problem with the compressor not pumping enough OR the expansion valve is staying open to much.
I do know that 2 identical systems can operate differently. I have a A model KW with a modified AC coil behind the grill instead of the original grill being the coil. It took 6 cans of durs-cool to get 45* at the vents. I curently have almost 4 cans in my GMC to keep the compressor from cycling. I did change my expansion valve and had to tie the bulb to the line on the new one, I could have it wrong and it isn`t reading temp properly causing me to use more gas than most? At hwy speeds I usually get 45* at the vents, if outside temps go over 100* it goes to 55*
I`m not trying to start a AC war, I`m just trying to help.
C. Boyd
76 Crestmont
East Tennessee
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| Re: some closure on my AC system [message #138489 is a reply to message #138367] |
Thu, 11 August 2011 15:20 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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I assume you have checked and the clutch isn't cycling the compressor due to the thermostat located in the cold plenum?
The discharge pressure puzzles me 125- 130 relates to 105 degree condenser temperature 110- 115 relates to 100 degree condenser. If any thing with the low side rising which is normal with more load the high side should be increasing also. If the clutch were cycling I could see this happening. If you are not sure the clutch is staying engaged you can jumper the temperature switch or connect 12 volts directly to the clutch temporary.
Roy
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: some closure on my AC system [message #138498 is a reply to message #138367] |
Thu, 11 August 2011 15:46 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Senior Member |
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C.Boyd,
Sorry I did listen to what you said, and do have the fenders out.
The suction line is cold comming out of the evap but I didn't check all the way back to the compressor, and the high side is hot, but not really too hot to touch. I will check the next time I have it running
Roy,
I'm really sure the compressor isn't cycling, I have the fender off and check it and don't see it or hear it turn off. I will jumper it next time I test it
My biggest point is that if I run just the dash evap (1500rpm), it's cold, when I turn on the fan to the secondary, it is cold for half a minute or so then warms up as does the dash air and I see pressure changes.
It just seemed to me that at 1500 RPM with little airflow over condensor the compressor was not able to keep up causing the low side to rise and the high side to go lower. Just like if the compressor wasn't turning at all...
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: some closure on my AC system [message #138514 is a reply to message #138498] |
Thu, 11 August 2011 16:33 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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When you say high side you should be able to hold the liquid line but if you mean the discharge line on the compressor you definately shouldn't be able to touch it as it will be quite warm.
Roy
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] some closure on my AC system [message #138523 is a reply to message #138498] |
Thu, 11 August 2011 17:31 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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On Aug 11, 2011, at 2:46 PM, Keith V wrote:
>
>
> C.Boyd,
> Sorry I did listen to what you said, and do have the fenders out.
> The suction line is cold comming out of the evap but I didn't check all the way back to the compressor, and the high side is hot, but not really too hot to touch. I will check the next time I have it running
>
> Roy,
> I'm really sure the compressor isn't cycling, I have the fender off and check it and don't see it or hear it turn off. I will jumper it next time I test it
>
> My biggest point is that if I run just the dash evap (1500rpm), it's cold, when I turn on the fan to the secondary, it is cold for half a minute or so then warms up as does the dash air and I see pressure changes.
>
> It just seemed to me that at 1500 RPM with little airflow over condensor the compressor was not able to keep up causing the low side to rise and the high side to go lower. Just like if the compressor wasn't turning at all...
I don't think that I had read before that your dash evaporator will cool fine but your aux one does not. I assume that you have them set up in parallel. I would suspect that the expansion valve for the aux. evaporator is not working properly.
Emery Stora
77 Kingsley
Santa Fe, NM
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| Re: some closure on my AC system [message #140917 is a reply to message #138469] |
Thu, 25 August 2011 12:06 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Senior Member |
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| C Boyd wrote on Thu, 11 August 2011 14:26 |
| Keith V wrote on Wed, 10 August 2011 23:35 |
I did some more testing today.
It was in the mid 70's so more normal pressures.
I knew the main evap was clean and I had the front off
I had my shiny and clean harbor freight A/C gauges hooked up
Engine running at 1500 RPM scaring women and small children.
I turned on the fans on the dash air and the secondary AC fan was OFF.
I added Duracool to get 20 PSI and the high side was 125-130.
Ran for about 10 minutes and it looked stable.
The evap was dripping and the low side was COLD.
I then turned on the secondary fan on high ( this thing has some serious airflow)
The discharge air on the secondary started out cold, but soon warmed up Hmmmm
The low side climbed to 25-28 and the high side dropped to 110-115
So it looks like the compressor can't keep up with both units running full blast.
Maybe at freeway speeds (2500RPM) it could, but not at 1500 rpm with no air flow through the radiator!
So I think with a large secondary evap, it's possible to overwhelm the compressor.
I still think the compressor is weak.
Now to get airflow through the dash vents...
|
Keith: I hate to keep harping on "sweating back to the compressor" thingie, but...... It ain`t no trouble to pull the right inner fender liner, about 3 minutes with a 3/8 socket, and look and see if the low pressure line is sweating at the compressor, 1500 rpm with a shop fan blowing on the grill. If not sweating add a little gas til it does then see what the AC vent temp and gauges say. Just from my experience with big trucks. I have no formal AC training and I do not know what the gauges actually do, I just use them to switch from a vacuum pump to gas. If the syatem will hold a vacuum it will hold freon, if the compressor runs and the low pressure line is sweating at the compressor and the high pressure line is to hot to touch you will have cold AC. If you cannot get the line to sweat at the compressor after adding gas then you have a problem with the compressor not pumping enough OR the expansion valve is staying open to much.
I do know that 2 identical systems can operate differently. I have a A model KW with a modified AC coil behind the grill instead of the original grill being the coil. It took 6 cans of durs-cool to get 45* at the vents. I curently have almost 4 cans in my GMC to keep the compressor from cycling. I did change my expansion valve and had to tie the bulb to the line on the new one, I could have it wrong and it isn`t reading temp properly causing me to use more gas than most? At hwy speeds I usually get 45* at the vents, if outside temps go over 100* it goes to 55*
I`m not trying to start a AC war, I`m just trying to help.
|
Keith: so I had stated I had almost 4 cans of duracool in my GMC, practicing what I had preached I went back to check if I was sweating to the compressor and found I was NOT. So I start letting gas out slowly from the low side till the compressor line was sweating good and had lowered my low side from 30 to 24. The discharge temp stayed the same, but hopefully it will hold temp better in traffic.
C. Boyd
76 Crestmont
East Tennessee
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