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Car Forum / Jeep / July 200699 Cherokee HVAC Problem
A recent 300 mile camping trip pulling a small tent trailer afforded an opportunity to better characterize the problems with the HVAC of our 1999 Jeep Cherokee. We'd taken it in the week before our trip with a complaint that the ventilation would randomly shut off the vents although the fan continued to run. Our repair shop found a technical service bulletin that was relevant, diagnosed a failing panel vacuum actuator, and replaced the unit. However, on our trip we had the same problem but now were able to observe that the ventilation shuts down under conditions of high manifold pressure (e.g., going up hill) but the ventilation was restored on level or downhill grades. Rapid acceleration on level ground also caused the ventilation to shutdown. This behavior was consistent regardless of whether the air conditioner was selected or just simple fresh air ventilation. We did not check whether it occurred when the selector was positioned for defrost. A possibly related problem is occurring with the "factory installed" cruise control. It used to be quite solid, keeping the speed within ± one mph--now it has a good five to ten mph slop and can take tens of seconds to resume the set speed. Fuel consumption has remained constant, we continue to get 20 mpg, in-town and on the highway with or without the trailer. I have noticed that the engine seems to have some hesitation and not quite the same acceleration lately but it is approaching 90,000 and is time for service. Any help would be appreciated. Janie Hi Janie, All manufactures design their computers to shut the air conditioner off if the engine is in danger of over heating. Maybe, add an auxiliary transmission cooler if you're going to haul a trailer again. God Bless America, Bill O|||||||O mailto:LWHughes3rd@aol.com http://www.billhughes.com/ > A recent 300 mile camping trip pulling a small tent trailer afforded an > opportunity to better characterize the problems with the HVAC of our [quoted text clipped - 28 lines] > > Janie Thanks, Bill. It wasn't overheating. That's the neat thing about my Jeep - it pulls my little tent trailer like there's nothing to it, and no loss of gas mileage either. <g> Janie > Hi Janie, > All manufactures design their computers to shut the air conditioner > off if the engine is in danger of over heating. Maybe, add an auxiliary > transmission cooler if you're going to haul a trailer again. > God Bless America, Bill O|||||||O > mailto:LWHughes3rd@aol.com http://www.billhughes.com/ Neither was a line of new cars stopped in traffic leaving Las Vegas, but as far as I could see everyone had their windows down. God Bless America, Bill O|||||||O mailto:LWHughes3rd@aol.com http://www.billhughes.com/ > Thanks, Bill. It wasn't overheating. That's the neat thing about my > Jeep - it pulls my little tent trailer like there's nothing to it, and > no loss of gas mileage either. <g> > > Janie A recent 300 mile camping trip pulling a small tent trailer afforded an opportunity to better characterize the problems with the HVAC of our 1999 Jeep Cherokee. We'd taken it in the week before our trip with a complaint that the ventilation would randomly shut off the vents although the fan continued to run. Our repair shop found a technical service bulletin that was relevant, diagnosed a failing panel vacuum actuator, and replaced the unit. However, on our trip we had the same problem but now were able to observe that the ventilation shuts down under conditions of high manifold pressure (e.g., going up hill) but the ventilation was restored on level or downhill grades. Rapid acceleration on level ground also caused the ventilation to shutdown. This behavior was consistent regardless of whether the air conditioner was selected or just simple fresh air ventilation. We did not check whether it occurred when the selector was positioned for defrost. A possibly related problem is occurring with the "factory installed" cruise control. It used to be quite solid, keeping the speed within ± one mph--now it has a good five to ten mph slop and can take tens of seconds to resume the set speed. Fuel consumption has remained constant, we continue to get 20 mpg, in-town and on the highway with or without the trailer. I have noticed that the engine seems to have some hesitation and not quite the same acceleration lately but it is approaching 90,000 and is time for service. Any help would be appreciated. Janie My wife and I have twin 1999 Jeep Grand Cherokees. Mine has no problems, as you describe, but her Jeep has the same problem. Since they are both over our 60,000 mile warranty, I found a cheap (meaning no money) fix. I put her control (on the right hand side) to the upper vents, for air conditioning (in the summer) and leave it there, never turning it to the off position. It takes maybe 10-20 minutes for the baffles to "set" but once they do, there they are. When heating season comes, change to the down (or up and down) position and it will take another 10-20 minutes to "set' but there you are. Never put it in the "off" position. I don't know if the Grand Cherokee system is the same as the Cherokee, and I don't know much, but that's what know, and hope it can help. Your vacuum reservoir is collapsed, or there is a vacuum leak. Earle A recent 300 mile camping trip pulling a small tent trailer afforded an opportunity to better characterize the problems with the HVAC of our 1999 Jeep Cherokee. We'd taken it in the week before our trip with a complaint that the ventilation would randomly shut off the vents although the fan continued to run. Our repair shop found a technical service bulletin that was relevant, diagnosed a failing panel vacuum actuator, and replaced the unit. However, on our trip we had the same problem but now were able to observe that the ventilation shuts down under conditions of high manifold pressure (e.g., going up hill) but the ventilation was restored on level or downhill grades. Rapid acceleration on level ground also caused the ventilation to shutdown. This behavior was consistent regardless of whether the air conditioner was selected or just simple fresh air ventilation. We did not check whether it occurred when the selector was positioned for defrost. A possibly related problem is occurring with the "factory installed" cruise control. It used to be quite solid, keeping the speed within ± one mph--now it has a good five to ten mph slop and can take tens of seconds to resume the set speed. Fuel consumption has remained constant, we continue to get 20 mpg, in-town and on the highway with or without the trailer. I have noticed that the engine seems to have some hesitation and not quite the same acceleration lately but it is approaching 90,000 and is time for service. Any help would be appreciated. Janie Hmm, this sounds the most plausible. I'll bring it to the attention of the mechanic so he can look further. Many thanks to the others who responded, too. Janie > Your vacuum reservoir is collapsed, or there is a vacuum leak. The older Jeep Cherokees (88-92) had a vacuum reservoir inside the right front bumper. Two vacuum lines went from there to the HVAC and other things like the speed control. The lines went under/behind the battery. Over time the line wore out (acid ate through) and the Jeep had both the HVAC and speed control problem. Look at the vacuum lines then see if there is still a vacuum reservoir. > Hmm, this sounds the most plausible. I'll bring it to the attention of > the mechanic so he can look further. [quoted text clipped - 4 lines] > > > Your vacuum reservoir is collapsed, or there is a vacuum leak. My husband looked and couldn't see a vacuum reservoir. Looks like we'll have to take it in and have somebody take a closer look. Thanks! Janie > The older Jeep Cherokees (88-92) had a vacuum reservoir inside the > right front bumper. Two vacuum lines went from there to the HVAC and > other things like the speed control. The lines went under/behind the > battery. Over time the line wore out (acid ate through) and the Jeep > had both the HVAC and speed control problem. Look at the vacuum lines > then see if there is still a vacuum reservoir. And the winner is.. Howard! Yup, battery acid on the vacuum lines. New battery, new vacuum lines, new shocks. Rides great! Thanks! Janie > The older Jeep Cherokees (88-92) had a vacuum reservoir inside the > right front bumper. Two vacuum lines went from there to the HVAC and > other things like the speed control. The lines went under/behind the > battery. Over time the line wore out (acid ate through) and the Jeep > had both the HVAC and speed control problem. Look at the vacuum lines > then see if there is still a vacuum reservoir. Thanks for telling us what your problem was. God Bless America, Bill O|||||||O mailto:LWHughes3rd@aol.com http://www.billhughes.com/ > And the winner is.. Howard! Yup, battery acid on the vacuum lines. New > battery, new vacuum lines, new shocks. Rides great! Thanks! > Janie Well since my lottery ticket yesterday was 0 for 7, thanks. Nothing like having been there for the answer. Thanks for posting the solution to your problem as many just fade away. > And the winner is.. Howard! Yup, battery acid on the vacuum lines. New > battery, new vacuum lines, new shocks. Rides great! Thanks! [quoted text clipped - 6 lines] > > had both the HVAC and speed control problem. Look at the vacuum lines > > then see if there is still a vacuum reservoir. I'll second that, thanks for letting us know how it turned out. Jeff DeWitt > Well since my lottery ticket yesterday was 0 for 7, thanks. Nothing > like having been there for the answer. Thanks for posting the solution [quoted text clipped - 10 lines] >>>had both the HVAC and speed control problem. Look at the vacuum lines >>>then see if there is still a vacuum reservoir. Or the vacuum check valve has failed... the symptom indicate that under conditions of low manifold vacuum (uphill, accelerating) there is insufficient vacuum to keep the vacuum motors in their selected position. The system was engineered to default to Defrost since that is a safety condition. Lots of Chrysler products had this problem back when they ran vacuum systems on their HVAC - ask a Dakota driver with the 4 cylinder - they were famous for this problem. ZJ, WJ... etc. switched to electrical actuators which have different failure modes and don't default to defrost. reboot >Your vacuum reservoir is collapsed, or there is a vacuum leak. > [quoted text clipped - 32 lines] > >Janie check the vac supply line on the engine for the hvac esp. if u have the 4.0 engine > A recent 300 mile camping trip pulling a small tent trailer afforded an > opportunity to better characterize the problems with the HVAC of our [quoted text clipped - 28 lines] > > Janie |
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