joh510 Posted June 23, 2011 Share Posted June 23, 2011 Have a mack rd model and trying to find out what the gauges should read on the air conditioner LOW pressure side and HIGH pressure side ?want to make sure its not over charged, because My clutch unit is not kicking off automatically..temp in my area in the summer is 70-90 degreesits blowing very cold air..any help would be great Quote Link to comment https://www.bigmacktrucks.com/topic/19490-air-conditioner-psi-what-should-it-be-help/ Share on other sites More sharing options...
bubbamobilin Posted June 23, 2011 Share Posted June 23, 2011 Have a mack rd model and trying to find out what the gauges should read on the air conditioner LOW pressure side and HIGH pressure side ?want to make sure its not over charged, because My clutch unit is not kicking off automatically..temp in my area in the summer is 70-90 degreesits blowing very cold air..any help would be greatAt high idle (1000 rpm's) and the fan engaged, the high side should be between 250 and 450. The low side should be between 30 and 40. Quote Link to comment https://www.bigmacktrucks.com/topic/19490-air-conditioner-psi-what-should-it-be-help/#findComment-80122 Share on other sites More sharing options...
joh510 Posted June 23, 2011 Author Share Posted June 23, 2011 At high idle (1000 rpm's) and the fan engaged, the high side should be between 250 and 450. The low side should be between 30 and 40.wow 250 - 450 ? that's high I never would of thought of that..Any idea what would make the clutch on the air conditioner compressor to stay engaged Quote Link to comment https://www.bigmacktrucks.com/topic/19490-air-conditioner-psi-what-should-it-be-help/#findComment-80126 Share on other sites More sharing options...
cgallamore Posted June 23, 2011 Share Posted June 23, 2011 check the line going into commpressor, it should be sweating up to the nut, but not on the nut.if the nut is sweating it has to much...... Quote http://www.bigmacktrucks.com/uploads/1272400769/gallery_4852_794_314995.jpg Link to comment https://www.bigmacktrucks.com/topic/19490-air-conditioner-psi-what-should-it-be-help/#findComment-80127 Share on other sites More sharing options...
joh510 Posted June 23, 2011 Author Share Posted June 23, 2011 check the line going into commpressor, it should be sweating up to the nut, but not on the nut.if the nut is sweating it has to much......Ok thanks I will check it out.. Quote Link to comment https://www.bigmacktrucks.com/topic/19490-air-conditioner-psi-what-should-it-be-help/#findComment-80167 Share on other sites More sharing options...
cgallamore Posted June 23, 2011 Share Posted June 23, 2011 i had a dm doing that. it has a thermostat thingy that makes comp. cycle.a/c guy fixed it, cant help with how?????????????it looks like a thermocupler on the coils inside. Quote http://www.bigmacktrucks.com/uploads/1272400769/gallery_4852_794_314995.jpg Link to comment https://www.bigmacktrucks.com/topic/19490-air-conditioner-psi-what-should-it-be-help/#findComment-80176 Share on other sites More sharing options...
Rob Posted June 23, 2011 Share Posted June 23, 2011 I usually charge by the superheat method. Eliminates the guesswork no matter the ambient temperature, humidity or varying factors associated with HVAC. Helps pinpoint problems in the system also if you know how to interpret the data.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/19490-air-conditioner-psi-what-should-it-be-help/#findComment-80177 Share on other sites More sharing options...
theakerstwo Posted June 23, 2011 Share Posted June 23, 2011 I charge them till the comp locks then let just enough off so comp will turn again. Well you would be supriced at how many guys think that is ok. Ever one has there way of charging them. There is no way of telling what pressure it will have but when you do them ever day you have a good ideal if its in range. We always put a charge in the system that is weighted and in specs of the factory. If its a system like is in my old truck thats been reinvented then i will charge it till gauges look good and then start to go up a little at a time till the temp starts to drop.Its over charged then and will burn the belt fast. This may take a hr to but if its on your own labor is cheaper. Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/19490-air-conditioner-psi-what-should-it-be-help/#findComment-80178 Share on other sites More sharing options...
Rob Posted June 23, 2011 Share Posted June 23, 2011 I charge them till the comp locks then let just enough off so comp will turn again. Well you would be supriced at how many guys think that is ok. Ever one has there way of charging them. There is no way of telling what pressure it will have but when you do them ever day you have a good ideal if its in range. We always put a charge in the system that is weighted and in specs of the factory. If its a system like is in my old truck thats been reinvented then i will charge it till gauges look good and then start to go up a little at a time till the temp starts to drop.Its over charged then and will burn the belt fast. This may take a hr to but if its on your own labor is cheaper.That is the point of "flooding" the evaporator coil. At the example not all of the liquid refrigerant that has entered the evaporator has "flashed" into a gas and therfore no longer rejects heat. Theoretically, you want this point of flash gas to be between 2/3, and 3/4 down the path of refrigerant flow through the evaporator. The expansion device controls this function. It is sized appropriately for the size of the evaporator coil. This keeps the evaporator from freezing up as the water, (humidity) in the air passes through the fins of the coil. Head, (high side) and suction, (low side) pressures vary depending on a multitude of factors including those mentioned earlier. Compound this with dirty coils, lack of adequate airflow through the coils, differing blowe speeds, varying engine and compressor speeds in automotive applications, many variables exist. Typically in an automotive application an 11 degree superheat using R134A is ideal and easily attained with proper maintenance of the system. This means clean coils and adequate airflow across them. Usually if you have over 325 psi on the discharge side of the compressor I look for a restriction someplace in the system as this amount of pressure is seldom required given my limited experience.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/19490-air-conditioner-psi-what-should-it-be-help/#findComment-80179 Share on other sites More sharing options...
Mike Posted June 24, 2011 Share Posted June 24, 2011 I charge them till the comp locks then let just enough off so comp will turn again. Well you would be supriced at how many guys think that is ok. Ever one has there way of charging them. There is no way of telling what pressure it will have but when you do them ever day you have a good ideal if its in range. We always put a charge in the system that is weighted and in specs of the factory. If its a system like is in my old truck thats been reinvented then i will charge it till gauges look good and then start to go up a little at a time till the temp starts to drop.Its over charged then and will burn the belt fast. This may take a hr to but if its on your own labor is cheaper. LOL...Glenn that sounds like the Air Force way. mike Quote Link to comment https://www.bigmacktrucks.com/topic/19490-air-conditioner-psi-what-should-it-be-help/#findComment-80184 Share on other sites More sharing options...
theakerstwo Posted June 24, 2011 Share Posted June 24, 2011 Yes Rob in most of the trucks i work on the engine fan should have engaged before 300 psi and the pressure has started down.If its at a 900 rpm idle and the fan cant keep the pressure under 275 or 300 its got problems. Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/19490-air-conditioner-psi-what-should-it-be-help/#findComment-80186 Share on other sites More sharing options...
theakerstwo Posted June 24, 2011 Share Posted June 24, 2011 Yes Rob in most of the trucks i work on the engine fan should have engaged before 300 psi and the pressure has started down.If its at a 900 rpm idle and the fan cant keep the pressure under 275 or 300 its got problems. Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/19490-air-conditioner-psi-what-should-it-be-help/#findComment-80188 Share on other sites More sharing options...
mickwoodie Posted June 27, 2011 Share Posted June 27, 2011 Have a mack rd model and trying to find out what the gauges should read on the air conditioner LOW pressure side and HIGH pressure side ?want to make sure its not over charged, because My clutch unit is not kicking off automatically..temp in my area in the summer is 70-90 degreesits blowing very cold air..any help would be greatSounds like youve had some pretty interesting advice on charging your ac system.if you want to simply check your system, grab the vapour line out of your evaporator with the engine running and the air con off. have someone turn the ac on and feel for the pipe to go cold, will take upto 15 seconds. (should drop to about 5-7 deg celcius, about the temp of a good cold beer). if it goes colder than this or starts to ice up then could be a problem. probably not an over gassing situation tho.more likiely if your compressor clutch is not kicking out it could be a thermostat issue at the evaporator (should be located under the dash on the cab side of the evaporator).in all honesty tho if the system isnot iceing up when your using it and is keeping the cab nice a cool then dont worry about it. its doing its job. Quote Link to comment https://www.bigmacktrucks.com/topic/19490-air-conditioner-psi-what-should-it-be-help/#findComment-80455 Share on other sites More sharing options...
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