| Roof and Dash A/C Outlet Temps [message #285911] |
Wed, 26 August 2015 13:10  |
gbarrow2
Messages: 765
Registered: February 2004
Location: Lake Almanor, Ca./ Red Bl...
Karma: 3
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I used a probe type meat thermometer and a flat reefer thermometer to read the outlet air temp of each of my roof a/c's. OAT was between 70 and 80 sitting in the driveway.
Both roof a/c's got down below 40F to about 36F on each thermometer.
Took a road trip to test the dash a/c with the same 2 thermometers. OAT a little warmer but still below 80. After 1/2 hour driving at country road and highway speeds the lowest reading was about 40 on the meat probe stuck into the below the dash outlet and 50 with the refer thermometer laying on top of and in the air stream of the same a/c register.
Dash system is charged with Duracool. Pressure on the low side at 1500 rpm was 1/2 way between 0 and 25 on my gauge of questionable accuracy. It has no increments in the green zone just zero and 25.
Question is: Is that as good as can be expected from the dash air? What should the outlet be on a proper system? I can add or bleed off duracool to see if it improves.
The dash compressor has over 200,000 miles on it and seems noiseyer than in the past.
As compressors age and wear do they become less efficient and affect cooling temps?
Any suggestions to improve dash air cooling?
Gene Barrow
Lake Almanor, Ca.
1976 Palm Beach
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| Re: Roof and Dash A/C Outlet Temps [message #285946 is a reply to message #285911] |
Wed, 26 August 2015 19:34  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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The dash system ain't great. However, make sure not hot water is making it to the heater core. The valve often leaks. Also make sure the entire evaperator core is getting cold. Low charge or low compression by the compressor can wind upnwith only part of the core cold, reducing efficiency. Make sure all the baffles are moving to the cool position, and are sealing properly in the air box.
--johnnu
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: Roof and Dash A/C Outlet Temps [message #285958 is a reply to message #285911] |
Thu, 27 August 2015 00:19 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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It would be nice if you had a more accurate low side gage. Is the suction line cold and sweaty ? not knowing the true pressure you could be a little over or under charged. As Johnny suggests the heat damper needs to seal tight closed and a manual shut off valve wouldn't hurt. Also your 76 should have the double floor vent.this is the vent you will want the air to blow out of not the other vents. Did you do the Zay Brand modification by sealing off the outside air intake and cut an even bigger hole in the firewall then he suggests for return air ? This will make a big difference on a 76. When you cut the return hole it should extend from the cockpit area up into the area behind the dash as large as the blower housing will allow as viewed from outside looking in with the inspection cover removed. My 76 blowes a lot more air with this modification. Is your clutch cycling off on the thermostat located in the blower compartment ? Most can be re calibrated if needed.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Roof and Dash A/C Outlet Temps [message #285963 is a reply to message #285911] |
Thu, 27 August 2015 01:00 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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When I check dash air conditioning on any vehicle I use a Walmart meat thermometer inserted in the center or closest vent to the evaporator. I am looking for around 40 degrees or slightly higher with the fan on full speed. Anything colder than that will cause freezing of collected moisture out of the air on the evaporator. Some, not all, vehicle AC systems have a thermistor mounted on or in the evaporator. When the temperature drops below the 40 degree mark, the compressor clutch is shut off until the evaporator warms up again.
A better measurement is to look at the difference of the incoming air vs. the air leaving the evaporator. That temperature drop is what you are really looking for and want to measure.
Note: Reduced refrigerant in the system LOWERS the evaporation temperature in the evaporator. If the refrigerant is really low then there will not be enough refrigerant to evaporate and cool the air going through the entire area evaporator. So yes, really low refrigerant levels can cause poor cooling but small losses of refrigerant will actually cause the evaporator to run cooler.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Roof and Dash A/C Outlet Temps [message #285972 is a reply to message #285963] |
Thu, 27 August 2015 09:20 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Make sure you are on recirc if you have it
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: Roof and Dash A/C Outlet Temps [message #285998 is a reply to message #285911] |
Thu, 27 August 2015 21:46 |
gbarrow2
Messages: 765
Registered: February 2004
Location: Lake Almanor, Ca./ Red Bl...
Karma: 3
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Thanks to all for info and suggestions. I am trying to determine if my system is working as it should before I start making any changes to it.
If 40F on a Walmart meat thermometer at the dual air registers below the dash on a 76 system is good for Ken B. that's good enough for me. I didn't measure the inlet air temp but the ambient temp was between 70F-80F. A 30 to 40 degree drop sounds reasonable.
Can't check the overall cooling of the evaporator without opening the air box- If I have to do that I might as well make the hole in the firewall modification and make a 100% recirculating system. But if I am getting a 40 degree outlet air temp I assume that the compressor, evaporator, condenser, etc., are all working and the refrigerant pressure is reasonably close to what it should be.
I am not getting any heat from the heater in the airflow otherwise I don't think I'd ever get 40 degrees out the air register.
If all components are working as designed then the only way to improve cooling is to make the modification of blocking ambient air in take and making a hole in the firewall to provide 100% recirculating system.
Not sure if that will keep my wife cool, but worth a try before moving on to a more modern motorhome with better insulation and an effective a/c system.
Gene Barrow
Lake Almanor, Ca.
1976 Palm Beach
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| Re: Roof and Dash A/C Outlet Temps [message #286003 is a reply to message #285998] |
Fri, 28 August 2015 00:14 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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When I closed off the osa and put the large hole in the firewall my wife usually complains that the air conditioning is too much and could I please warm it up a bit .that is when the out side temperatures are below the low 90's. If it is really hot out you will need all the cooling you can get. At least out here in the west we don't have to deal with high humidity. When you increase the air flow over the evap coil the suction pressure should rise some. When you get around to the modification you won't believe the difference in air volume but you need to open the firewall as much as possible or you won't get the air volume that is needed.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Roof and Dash A/C Outlet Temps [message #286012 is a reply to message #286003] |
Fri, 28 August 2015 07:25 |
gbarrow2
Messages: 765
Registered: February 2004
Location: Lake Almanor, Ca./ Red Bl...
Karma: 3
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Roy,
Thanks for the suggestions. With the input I've received I'm concluding that the hole in the firewall is my only option to improve cooling. Did you post any pictures of your modification? Or can you direct me to any others? I know Ken Henderson posted something years ago. I'll try to find it on the photo site.
Gene Barrow
Lake Almanor, Ca.
1976 Palm Beach
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| Re: [GMCnet] Roof and Dash A/C Outlet Temps [message #286022 is a reply to message #286019] |
Fri, 28 August 2015 09:44 |
gbarrow2
Messages: 765
Registered: February 2004
Location: Lake Almanor, Ca./ Red Bl...
Karma: 3
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Senior Member |
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Ken,
Thanks. I found the album. Your photos are very helpful. Where can I get the thin foam used to seal the doors? What is the purpose of the diverter added to the inside front wall of the h/e box as shown in Zay Brand's drawings for 73-76 a/c mods?
Are you allowed to fish off the fantail of that Rhine river boat? Would like to see pictures if you and Jim H. find the time to post.
Gene Barrow
Lake Almanor, Ca.
1976 Palm Beach
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| Re: [GMCnet] Roof and Dash A/C Outlet Temps [message #286034 is a reply to message #286022] |
Fri, 28 August 2015 12:02 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Ken really got into his modification of the a/c system. I didn't do the divider . Karen had a really nice shot of the hole in the firewall but I don't know if it is in the photo site. Keep in mind the total area of the opening should equal the opening area of the blower input housing area. Also you will probably want a 1/4" square mesh screen over the hole so your socks don't get sucked into the blower. I got my door gasket material at Home Depot .
Roy Keen
Minden,NV
76 X Glenbrook
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