terryt Posted February 14 Share Posted February 14 i have a 1990 Comanche 4.0 with factory air and the only place the air will come out is the defroster. I have replaced just about all the vacuum lines with the exception of the control unit and the lines going into the control unit Does anyone have any suggestions? I am still searching for answers as to why my tach does not work also Link to comment Share on other sites More sharing options...
Pete M Posted February 14 Share Posted February 14 did you replace the vacuum line running to the ball in the front bumper? Link to comment Share on other sites More sharing options...
terryt Posted February 14 Author Share Posted February 14 IT DOESNT APPEAR TO BE BAD Link to comment Share on other sites More sharing options...
AZJeff Posted February 14 Share Posted February 14 The symptoms of “defrost only” air venting from the heater box is a sure sign of a vacuum leak. Have you actually tested the ball-shaped vacuum reservoir to see it hold vacuum? Have you inspected the heater control assembly for possible cracks or leaks? you say you replaced all the vacuum lines. Did that include the one to the reservoir? Link to comment Share on other sites More sharing options...
terryt Posted February 14 Author Share Posted February 14 no i have not is there an easy way to test for leaks? Link to comment Share on other sites More sharing options...
terryt Posted February 14 Author Share Posted February 14 that line appears okay but i will replace it if you think that is a possibility how do you check the ones at the control it is so tight i can hardly get it to pull out? Link to comment Share on other sites More sharing options...
rokinn Posted February 14 Share Posted February 14 https://www.harborfreight.com/dual-vacuumpressure-hand-pump-kit-56803.html Or some version thereof. Link to comment Share on other sites More sharing options...
terryt Posted February 14 Author Share Posted February 14 how do i use it? Link to comment Share on other sites More sharing options...
AZJeff Posted February 15 Share Posted February 15 The easiest way to test the ball is to first REMOVE IT and inspect it visually for cracks or places where the two haves are bonded together and have separated. Then take the vacuum pump suggested above, and connect the hose from the pump to the nipple on the canister ball. Pump the handle a few times and watch the guage. If the guage on the pump drops back to zero in just a couple of seconds, the canister ball is leaking. there is a less expensive vacuum pump that Harbor Freight also sells that will do the job, if money is tight. https://www.harborfreight.com/brake-bleeder-and-vacuum-pump-kit-63391.html Link to comment Share on other sites More sharing options...
terryt Posted February 15 Author Share Posted February 15 And if it is good? How do i test the vacuum lines at the control panel? Link to comment Share on other sites More sharing options...
AZJeff Posted February 15 Share Posted February 15 Testing the vacuum system is pretty much start at the intake manifold by applying vacuum at the hose connection there. If it fails, move to the next juncture in the vacuum system, and apply vacuum there. Repeat on down the line until you get to a junction where you no longer have a vacuum failure. at that point, you now know where the vacuum leak is, and you then start inspecting the components at that juncture for cracks, dry rod of hoses, etc. having a vacuum diagram for your MJ will help you know where to look. Link to comment Share on other sites More sharing options...
terryt Posted Thursday at 05:43 PM Author Share Posted Thursday at 05:43 PM On 2/14/2025 at 8:33 AM, Pete M said: did you replace the vacuum line running to the ball in the front bumper? I figured it out (thanks to all of you) it was the vacuum line going to the ball Now what can i do for the tach that does not work? Please tell me where to look! Link to comment Share on other sites More sharing options...
Pete M Posted Friday at 01:07 AM Share Posted Friday at 01:07 AM what's the backside of the cluster look like? they are known for corrosion issues. Link to comment Share on other sites More sharing options...
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