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Rawze · 07-01-2019, **(Subject: RE: Prostar ac )**

Someone on phone yesterday was asking me same stuff as mentioned on here,.. they also started asking how to force it to work. I thought i would mention this, as it is likely someone's next question...

The A/C on the prostar, here is the basics of what you can and cannot get away with, believe me, I learned this the hard way playing with mine...

Besides ensuring the mechanical parts of the system are working and are in good health,.. including blend doors, etc (the place to always start when servicing A/C) ...

Method(s) for helping the factory cab-controller to be "more happy" and not fault out the A/C so much ...

* Making sure the Ambient temp sensor for the engine is reading OUTSIDE TEMPS and not 10+ or even 30+ degrees higher because it is mounted under the truck or hood somewhere and it reads high due to engine temps.

* Making sure the thermistors on the passenger side of the truck are reading correctly. - Easily done by having a spare (known good) sensor and taking an ohm-meter/multimeter and comparing resistance at room temp on them. Making sure they are all reading somewhat same when system is off and they are all same as outside temp. - Really low resistance on one or all of them (like 300 - 500 ohms or less),.. THEY ARE ABSOLUTELY BAD! - I have had some come right out of the box like this from new.

* making sure the condenser and the evap. are working very well. NO dirt of grime in them to slow down air flow or cause efficiency losses. Same with cab filters both front and rear bunk.

* Making sure ALL of the fuses in the dash panel are NOT TARNISHED!..- Same is what is described in this post(s)...
http://rawze.com/forums/showthread.php?t...1#pid12861

* making sure the expansion valve is not plugged up with stop-leak,.. seems everyone these days is stop-leak+dye happy and that is a big killer of A/C on prostar. - The system hates that stuff!. - If you have a leak somewhere-- FIX IT!, and if you can't find you leak,.. PUT A SMALL BALOON that fits tightly OVER THE SERVICE PORTS and wait a while! - YOU WILL FIND YOUR LEAK because 9 of 10 times it is loosing pressure all the time is because of bad schrader valves! - because some moron put a dirty, dusty service tool on it, or did not bother to clean the valves before connecting to them.

* resetting it when it acts up by installing a reset switch like mentioned in this video...
https://youtu.be/flXkmAzsV7E

* LASTLY,.. AND VERY MUCH OVER-LOOKED!!!! --- IS THE FACT THAT PROSTAR IN PARTICULAR --> THE EXHAUST IS VERY CLOSE TO THE UNDERSIDE OF THE CAB--- AND NO PROSTAR COMES FACTORY WITH A FULL EXHAUST WRAP!!!! ---<<<< WRAP THE EXHAUST PIPING ALL THE DOWN ITS LENGTH AND IT WILL BE 10 -20+ DEGREES COOLER IN THE CAB ALL THE TIME!
I have made several mentions of this over the years on here. hers is one of those that came up in a search: http://rawze.com/forums/showthread.php?t...6#pid20496

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Things you cannot do on your own to force it to work...

* You cannot just jumper the compressor. It will make so much pressure, it will blow the guts out of the relief valve or blow apart the compressor. - This will make problems much worse.

* You cannot just jumper the engine fan to have it run non-stop to try to make it cooler,.. this will kill your fuel mileage so badly that you can't make a profit. Keeping the engine fan on at idle to help the A/C along a bit is not a problem though.

* You can't just jumper out the thermistors on the passenger side. The cab controller checks them at intervals to ensure they are changing in value AND that they are within a certain range compared to outside temps. Jumping them out usually makes the system fault out at exactly 10 minutes after the first time the compressor kicks in. I know this because I tried several ways to fool it. - I even resorted to putting resistor bank on a small 12v relay that activates same time as the compressor clutch, so that the resistance changes, .. this fools it some,.. but after a while it figures this out too and faults it anyways.

* you can't just have the compressor clutch tied directly to the high pressure sensor through some control means, based on pressure regulation alone. - Tried this too. - The thing makes cold air, but the damn evap core freezes up all the damn time, and if you bleed the system so that it does not, then as the weather changes, it freezes up any ways. I even tried resorting to modifying the expansion valve to get this to work,.. still a no-go,.. still problems with having to shut it off all the time to let if thaw out after its blowing hot-arsse air out the vents.

* There is however one advantage to controlling the A/C compressor yourself,.. and that is the fact that the blend door and blower motor system IS NOT TIED TO THE CAB CONTROLLER.. it is a completely separate system, located on the circuit board right behind the control knobs. - This means that no matter what you do to the compressor side of things,.. it will not effect the operation of these systems. This also means that if the blower(s) are not working properly,. or the blend doors are not working properly,.. it is NOT a problem in the cab controller.

* What I resorted to, through much experimentation on mine any ways,.. is to ..
-- put a relay on the clutch circuit and control the compressor on my own based on 2 things. They are BOTH the high pressure sensor -- AND-- a separate temp sensor I installed in the evap core to tell me when the system wants to freeze up. I also resorted to manually controlling the engine fan, makng it come on when the pressure gets to above 250-psi or so. This works well to improve its efficiency without too much loss in fuel mileage in engine, as it will rarely ever see that high of pressure when going down the roads above 30 mph or so due to better cooling.

That is what i know about this system,.. and what ? I have done. i resorted to the arduino idea, because I got so sick of mine not working, just like everyone else I have met that owns a prostar. mentioned here:
http://rawze.com/forums/showthread.php?t...2#pid15312

Making an arduino project to bypass the cab controller on the A/C is not recommended unless someone has some programming and electronics background themselves. You have to be willing to chase your own issues with it. No one else will ever be able to work on the A/C system for the truck if you resort to doing something like this ... so it is NOT recommended for the average truck owner/driver.