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A/C pressures

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Just replaced my a/c compressor and the mechanic notes that the pressures were getting high and the fan wasn't engaging. Took awhile for the fan to kick on. So at what pressure is it supposed to get for the fan clutch to kick in? --- I am here: http://tapatalk.com/map.php?fvx4cf 2003 Ram with gauges and a Smarty! Not much more. Sent from my iPhone using Tapatalk

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  • Owner

Ummm... As far as I know as the pressure increases to a point around 450 PSI on the high side the compressor will be shut down. As far as I know there is no connection between the A/C and the fan on a 03. Like my 02 the there is a high pressure switch and a low pressure switch. As long as the pressure are between those 2 limits the compressor runs but as soon as it leave those to limits the compressor is shut down to protect the system.

  • Author

Someone once told me the electro/viscous fan is tied into the a/c somehow. The fan will spin a little faster when the a/c is to pull air over the condenser. --- I am here: http://tapatalk.com/map.php?4w0yle 2003 Ram with gauges and a Smarty! Not much more. Sent from my iPhone using Tapatalk

  • Author

From what I have researched, the 3rd gen Ram A/C really sucks and for it to spike this high is common place. No real way for the fan clutch to engage when the A/C clutch kicks in to cool the condensor. So from what I have read and seen pictures people are installing a 16" electric fan on the front of the condensor and wiring directly to the A/C clutch. I have ordered my fan and hope to be installing soon.

  • Author

Nothing in the ECM to tell the fan to engage when the high side pressure increases. Cold engine the fan doesn't spin fast enough to cool the condensor. I bet most 3rd gens added a can of freon a lot cause of this. --- I am here: http://tapatalk.com/map.php?hvuzte 2003 Ram with gauges and a Smarty! Not much more. Sent from my iPhone using Tapatalk

  • Owner

Adding more freon make the output air warmer... :duh:The lower the low side pressure the colder the output air becomes. Output temp in theory is the inside ring for R-134a as you can see I marked out the 35-40*F area. (Typo'ed the temps! :banghead:)post-2-138698186414_thumb.jpgBack in the day when I recharged R-12 freon on refridgrators typically it was 2-5 PSI on the low side. Then for the old 73 Dodge Charger which was also R-12 I always went for 40 PSI that kept the evaporator from freezing up for down in Cally on humid days.

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3rd gen a/c takes a lot of hits, but of the 3 rigs I own my 05 has the best a/c. It really works great and will freeze you out on a hot day in no time. The fan does engage on some trucks, not sure of the ECM logic, but I think the auto truck run the fan with the a/c more.

It does not, but I would guess that the fan running would help warmup time. With the thermostat closed you get very little radiant cooling from the air over the block, but the fan takes hp and increases the load.

  • Owner

...but the fan takes hp and increases the load.

Either electric or mechaincal the load is placed on the engine either at the belt pulley for the mechanical or at the alternator for the electrical. So no matter what you now have two fans to power on the engine now. I would rig the electric fan to only come on with the compressor if your looking to gain back from some of the load.

I just read through this thread and am confused as to how you use your rig. The only gain you will get with the electric fan is while sitting stopped in 100+ degree heat. My 05 also has the best ac I have ever had in a vehicle even in 90+ high humidity heat sitting at idle it will freeze me out and I am a heat hater and I have to turn it way down.Did you put the electric fan on just because the mechanic said the pressures were high or is the ac performance low?Has the condensor radiator and aftercooler been cleaned out lately? if they are dirty lt will not get enough airflow across the fins to cool it down regaurdless of fan power pushing or pulling and lack of airflow through the condensor causes high pressure. But without knowing what the pressures actually were ambient temps and duct temps were or are It is hard to help much.This thread started talking about an AC Compressor swap and then jumps directly to fan discussion with no other reference to AC performance.

  • Author

It started as to what pressures should the AC be at, then turned to other things. The reason for the pusher fan is cause the trucks fan does not really kick on when the compressor is started until it warms up. Which causes the pressure to really spike. This will help the passenger side cool a little more also. The cores are clean from what I can tell. --- I am here: http://tapatalk.com/map.php?1ktqr2 2003 Ram with gauges and a Smarty! Not much more. Sent from my iPhone using Tapatalk

What are the actual pressures? How will it help the passenger side?The fan is still working just not at full capacity until it is needed, so back to my original question is the AC working fine or not? And do you just sit and idle a lot? Any speed over 25 mph and the fan isn't doing much anymore all your airflow at that point it being pushed through and not pulled by the fan. I know tons of guys who run absolutely no fan at all and do not see AC issues until stop light to stop light on hot day in town.

  • Author

What are the actual pressures? How will it help the passenger side? The fan is still working just not at full capacity until it is needed, so back to my original question is the AC working fine or not? And do you just sit and idle a lot? Any speed over 25 mph and the fan isn't doing much anymore all your airflow at that point it being pushed through and not pulled by the fan. I know tons of guys who run absolutely no fan at all and do not see AC issues until stop light to stop light on hot day in town.

At my friends shop with gauges we saw close to 400, cold truck and outside temp of mid 60's. Not even close to what summer time temps get down here is SC. I know the freon level is right also because it was filled using a scale. The passenger side temp is warmer than the driver and this will help in colling the freon. No idling unless I have too for traffic. I try to keep that to a minimum. Only time I ever extend I after pulling my fifth to let the turbo cool down. --- I am here: http://tapatalk.com/map.php?vwxn2w 2003 Ram with gauges and a Smarty! Not much more. Sent from my iPhone using Tapatalk

3 things will cause high pressures like that, either a plugged front end like I described or a partially plugged orifice tube or receiver drier. How did the compressor fail? If anything went through the system from a failed compressor it will end up at the orifice tubeand drier and cause high pressures as well. What were the low side pressures and what were the duct temps?Did you pull the system into a vacuum before charging the system after the compressor swap?

  • Author

Clutch seized together. Wouldn't spin. As for the pressures I have read comments in other forums and they state the exact same thing about the pressure spikes due to the fan not kicking in. Which is turn causes the freon to be puked out. The additional pusher fan is to help with the pressure spikes when the engine fan is not engaged. The pusher fan is wired to come on when the clutch engages. --- I am here: http://tapatalk.com/map.php?zfbucv 2003 Ram with gauges and a Smarty! Not much more. Sent from my iPhone using Tapatalk

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