Ok- Cruising down I-10 from Lafayette to Houston. Outside temp was around 85. A/C was working fine,The entire trip, blowing out nice cold Air. As soon as I get off I-10 and sit in some traffic, Stop and go...A/C blows warm. Rev the engine...A/C blows cold again for a few minutes. It seems anytime I am up and running the A/C works fine. But driving around town, Stop and go type traffic...the A/C performs poorly. The Belt is good. The freon is full. Any thoughts?

 

You Might Check The Pressure Switch

 

Your radiator isn't dirty from oil from the puke bottle is it? If it is it could be restricting air flow through the condenser when stationary. You might also want to check your engine cooling fan.

 

Check the frequency of your cycle on /cycle off at idle of your compressor, if thats normal I'd look at the blend door of your heater / ac and make sure its closing at lower speeds/ idle.

I'm assuming that the blend door runs off vaccum, could be wrong though.

 

Blend door on the 99 is electric. How do you know the freon charge is good?

 

I'll have to keep an eye on this one. Although mine seems to do the reverse. Almost seems to warm up slightly when driving fast and cool better at slower speeds.

 

I'll say normal to this. Under load it's designed to shut off to give the extra HP to the motor so pulling a load up a hill my ac will shut off (fans still running) until I crest the hill and then back on to cold.

 

Hydrauk, here's what happened to me. In Sept 05, I'm hauling Fema campers to Baton Rouge & had to change a blown tire on a camper. My a/c had been blowing ice cold all the way from Indiana hauling this 7000lb trailer. I stop in Hammond, LA and let the truck idle with a/c on for my dog inside. After about 15 minutes, I get in the truck to get a drink & its blowing HOT air and my dog is ******! I rev the Cummins a few times and it starts blowing cold again for about 5 minutes. So I finished changing the tire, stopping every 5 min to rev the motor to keep the dog cool. I never figured out why it did that & the compressor clutch eventually seized a few months later. A guy at Autozone told me I should add a can of r134, which I did, but I think it made the problem worse. I know that pulling a load didn't affect the situation. Sorry for the long reply, your post reminded me of that issue. Good luck!

 

This is new to me never heard of an A/C system shutting down for more power. These trucks do not have the technology or logic to know when you crest a hill or dont need more power. Sounds like your a/c may have a problem too. Any way back to the original question. How do you now that you have enough freon? Also check the air flow across the condensor. When you are traveling down the road you have alot of air flow when you slow down your air flow slows down and if your condensor is dirty or the fins are bent over or the fan is not working properly the you will have the problems you discribe.

 

Not to hijack the OP but I swear I read there was a sensor that would determine engine load and shut the ac system down, obviously it doesn't know if you crest a hill but by some way knows the load on the engine and shuts off the AC to provide more HP to the engine when load decreases the AC is back on. I know for a fact it's that way on Subaru's. I'll try to dig up some info.

 

hi
i have the same prob !
but i think i know why !
the fan clutch is not doing its job at low speed !
i had a locked fan clutch which i replaced with a fan clutch from autozone and i can hear it ingage at times , but the engine / rad temp must be app 200 to get it to ingauge . if engine temp is only 185 and sitting in traffic it does not engauge and draw enough air across the condensor !
listen for your fan clucth to ingauge and the fan noise !
now the good news is there is a special fan clutch from dodge that does ingauge at a lower temp , cant remember if it is 160 or 180 * ?
i had the part no and lost it after i priced the clutch app $200.00 as apposed to autozones $50.00 .
i will be getting the mopar one as soon as i find the part no agin !
does anyone know the part no?

 

Mine has NEVER cut off during a crest of a hill or under load. Ever. And as I'm in the middle of redoing my ac right now, there is no such control in the system that would make this possible. It's a simple independent system.

I had a co-worker that had an issue similiar to this. He had got his truck used. His issues turned out to be the orfice tube was installed backwards. But that can't be your issue because the orfice tube is built into one of the lines and is not really serviceable, but that does point me towards some sort of ac issue. And the most common issue with these things are the evaporator cores leaking. At times when mine was low, it would do this. Not all the time, but sometimes.

I'd say your best bet would be taking it to a shop. There's not really too much you can do yourself with these systems, especially if you don't have all the tools to do so. This can be as simple as a bad pressure switch, which is probably a $15 part, but the system has to be discharged and opened to refill it. Most people don't have the stuff sitting around to do this. Usually your sytem leaks, and if you get the stuff, you fix it then it sits around so long you forget where it's at, or like me, all your stuff is for R12, not R134.

You can throw alot of $$$ at it guessing. A good ac shop will know real fast whats wrong. A really good shop will know most of the time what is is when you tell them what happening. Beleive me, yours is not the first Dodge that had an ac crap out and by far, will not be the last. A good shop has fixed thousands of these things.

 

Read under Throttle Position Sensor bottom right

http://books.google.com/books?id=Yn9...=en#PPA1140,M1

This is general information and not specific to our trucks but the technology is out there and has been for years.

 

when i worked for dodge and my ctd does the samething at WOT.

 

I have pulled a lot of heavy trailers up some long steep grades in 90+ degree weather & my a/c never cut off either. I don't think that stuff about a/c cutting off on a hill applies to 98-02 CTD's.