River_Rat

I have a 99 Cherokee Classic, when i bought the jeep the ac blew hot air, i had the system charged and it blew cold for the first 5 minutes at idle, i put it in drive hit the gas and immediatly blew hot air again, i figured i had a leak somewhere and all freon leaked out, never fooled with it again, yesterday i flushed the radiator, heater core, and all hoses, put new water pump and clutch fan in it, filled radiator and started the jeep, all of sudden ac blows cold again at idle, i let the jeep warm up to normal temp, ac still blowing cold, put it in drive hit the gas and immediatly hot air again, so my question is why is it doing this? Ac compressor problems?

Turbo X_J

What pressure at ambient temp?

Pelican

Since it only does this on acceleration, I would suspect a leaking vacuum line somewhere between the reservoir ball and the firewall (often around the battery),

River_Rat

I do have a vacume line leading to no where, been like that since i bought the jeep, i will post a pic of the line, never could find where its suppose to go or a diagram of the vacume lines or anything but yeah, engine runs great even with that line, no check engine light, plenty of engine power, i will show pic of the line maybe someone can tell me where its suppose to lead too, just another of many problems with this jeep, previous owners rigged a lot of things

CCKen

Go here and look at post #51.

https://www.cherokeeforum.com/f2/gre...e-6558/index4/

Also, there should be a EVAP system diagram on the emission label on the left firewall.

AzItaliaSS

I recently during a flush and drain severed my air vacum line when reaching in the side of my "open" bumper to loosten **** or drain plug of my radiator. I had similar issue, air would be on a normal but as I enter the freeway under accelartion, my air would warm and also slow as if you turned the dial one 4 to 1. upon exiting and slow accelartion it would briefly return to higher volume air and colder. The vacum line was then put back onto the black ball via a napa hose line I slid over each end, and WALA my air is back and no issues.
So maybe you have similar going on. check the ball I would say..GL

River_Rat

here are the photos for the vacume line, where it starts then runs along the fire wall around to the passenger side then ends there, i looked all over of where it might connect to and can not find anything,

husky_wolf

This just happen to me a couple of days ago, it was a vacuum line crack. Do you have a vacuum line going into your fire wall in the passenger side? If you go to my threads you'll find a pic of my rig for that line. Also look very closely at the lines running passed the battery I had to take the line off and blow air into one end while plugging the other side to find the air leak. Hope this helps

PocketsEmpty

It looks like the line leading to the vacuum canister which is located right behind the front bumper on the passenger side (assuming stock). That would be the source of your vacuum leak and likely the problem. It is likely causing the blend door to change to the warm side when you accelerate.

CCKen

That tube used to go to a leak Detection Pump (LDP) that someone has removed.

The CEL bulb has probably been removed as well to hide the EVAP DTC CEL.

The white placard on the firewall should show the emissions plumbing, and the LDP.

River_Rat

Would the missing LDP be responsible for the ac problems? Check engine bulb does work iv had the light come on a few times due to spark plugs an distributor cap bad, so it does work, so this leak detection pump is somthing that needs to be replaced?

CCKen

If the firewall placard shows an LDP, you should have one installed. If the placard doesn't show an LDP ten you don't need to install one. For '99, LDP's were installed to meet California emissions standards. The placard would state this, otherwise it would state it meets Federal emissions standards.

You can cap off the fitting at the intake manfold if the LDP is not required on your Jeep.

Can't understand why you wouldn't get a CEL with no LDP. Was the PCM ever replaced in your Jeep?

Bustedback

I had a 89 Chrysler Lebaron Turbo Coupe that would blow nice and cold when I first started the engine, but as soon as I put it in gear and started to move the A/C would blow hot just like you describe with your Jeep. It was a broken blend air door that was causing the problem. As soon as I started to move the door would swing back and close off the cold side of the HVAC box. I replaced the door and enjoyed the cool air until I sold that POS.

River_Rat

PCM never been replaced to my knowledge, i bought the jeep few years ago from local mom and pop dealer and they couldn't tell me much about it, since i havent had the CEL on and jeep has ran fine with out it i will just take that line out and cap off at the manifold like you said, as for the blend door I'll have to check that out, where would it be located on a 99 jeep if anyone can tell me? Thank you ALL for your help and input!

Bustedback

The door is inside the HVAC case under the dash. You have to remove the dash in order to remove the HVAC case to change the blend air door. It's a pretty big job.