A Test For You Auto Savy Guys.

Tiny
BOATS
  • MEMBER
  • FORD
I drive a 83 Merc Marquis with 114,000 miles. I recently had a/c recharged. With car in park, or in gear with brake applied, it blows very cold and all damper doors and vents work correctly. When driving, as I depress accellerator the dash damper door will close allowing me a face full of hot air. As I let off the throttle, the doors will regain the vacuum to open and all is well. I have thoroughly been through this vacuum system checking and exploring, but this is the first time troubleshooting one. At idle, directly off the carb I have 16-18in vacuum. In gear with brake I hold a consistent 12-13in. Every vaccuum motor and line in the interior is proven to work and hold vaccuum as well as the damper door selector switch. Under the hood, I have located all the little vacuum ports, and retarders, and valves, and lines and none have leaks or defects. Air pump is pulling good air through the by pass valves and egr and hoses and all that. So why is the throttle pulling so much vaccuum away from my a/c? Would this point to the carb not producing enough vaccuum to handle climate control and the transmission? Will the carb need to be rebuilt, or can the vaccuum be boosted somehow? O yeah, transmission modulator is new also with no leaks and shifting properly. Ive also checked all the in line check valves along the way and also added a few redundant ones just to eliminate a variable here. To everyone thats sick of reading this, Ive got at least a year & 1/2 off and on straightening this out and Im running lean on nerves. Do me a favor and prove the ignorance of my ways.
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Tuesday, May 9th, 2006 AT 12:50 PM

4 Replies

Tiny
PEPPERMRJ
  • MEMBER
The further open the throttle the less vacuum. That is the purpose of the check valves, to maintain high vacuum when little is available. If they are indeed working properly then there iis a leak in the vacuum line or vacuum motor/controller

Good luck and let us know what you find. :)
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Tuesday, May 9th, 2006 AT 9:18 PM
Tiny
BOATS
  • MEMBER
Well I found half the problem. My new coolant line vac selector was leaking under the hood. Fixing that, my damper doors are holding correct positions while driving. Finally. But now the other problem is still there, while driving with the a/c on the air will turn hot while using the throttle even though the doors will hold their position. Now that the vacuum leaks have all been fixed, could the problem be of a more mechanical nature? - Egr, air bypass valves, something else I havent come across yet?
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Tuesday, May 30th, 2006 AT 8:11 AM
Tiny
TAURUSWHEEL
  • MEMBER
Is there any chance you have a vacuum-controlled heater valve on one of your heater hoses? It would be in the engine compartment, seems Fords, older models, some may nave used a cable actuated valve, others a vacuum-controlled valve, just pulled this out of left field.
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Tuesday, May 30th, 2006 AT 7:22 PM
Tiny
BOATS
  • MEMBER
Actually, the chilton calls it a temperature sensing electric valve. On my car it has two vacuum lines and an electrical connector as well. I bought a new one recently and it was at this vacuum plug that I found the problem to my damper doors. Since the problem was at the area where the plug meets the valve, I pulled the plug out and inserted a piece of vac hose in between the two lines allowing air to pass to each other. Im undecided right now if I shouldve plugged them both independantly instead. Your thoughts on this?
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Wednesday, May 31st, 2006 AT 8:27 AM

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