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1989 Town Car AC Issues

I have a 1989 Lincoln Town Car Signature Series with 215,000 miles. The problem is that you get heat through the dash vents when you accelerate the engine even with everything turned off and temperature set on 60. If you are sitting still idling or going down hill with the air conditioning on everything runs fine until you begin to accelerate the engine. I have had my car to the local Ford Lincoln Mercury dealer twice and they were unable to locate the problem. I have replaced the main vacuum harness coming from the exterior firewall through the passenger cabin that goes to all the vacuum pumps and main auto climate controls which is all one piece. I have also replaced the ambient air temperature sensor and main vacuum control on the auto climate system (where you select which mode you want such as temperature and floor vent, etc.) I also have tried another blend servo pump (behind the glove box) and the problem still exists. You can hear a door or something move when you accelerate the engine and hear it move again when you let off the gas. I think I also tried the vacuum check valve on the exterior firewall also. Are there any electrical/vacuum controls under the hood that would malfunction and cause this? Please Help!!!!!!
Thanks Bill….
Justin in Virginia
Hello Justin –
Loss of cool AC on acceleration and defaulting to heat is a common problem in Town Cars of that era. It is always caused by one or more vacuum leaks. Vacuum leaks in the AC system can develop any where that the vacuum is routed. According to your report you have replaced many of the more likely problem parts but I don’t know if you replaced them with new parts, good known parts or only unproven used parts. Another point is that replacing parts without proving that they are actually defective is never the best way to go. This method is usually very expensive, more time consuming and frustrating.
Assuming though that all of the items that you have already replaced are indeed in good working order there are other areas where leaks can be found in that system. They are the Vacuum Reserve Tank, Cold Engine Lock Out Switch (or CELO) and its vacuum lines (located in one of the heater hoses) any vacuum line and any of the under dash vacuum mode motors, etc. As mentioned above, any suspected items should be properly tested for leaks before condemning. If no leaks are found anywhere then you or your mechanic must backtrack and revisit problem areas. Some leaks can be elusive and therefore time consuming to locate but it can be done. Whenever I work on these exact problems I always have the vacuum diagram within reach, therefore I would advise that you or your mechanic also have one available.
If we can help with any further information, manuals, diagrams or parts please let us know. Please advise us Justin when you locate the problem so that we can post your success on the blog. Good Hunting!

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