Thanks for checking Pete.

This means you are losing vacuum. The engine intake produces the vacuum and stores it in the reservoir, then the dash mode doors use it. So all you need to do is find the leak. You need at least 10inhg of vacuum at all throttle ranges to keep enough vacuum to operate the mode doors. So start at the supply to the climate control head to see if it is dropping there which will shorten the area you need to test, to the engine and lines at the engine and reservoir. Below is a ford file to help out.

http://wikisend.com/download/254064/1121.pdf

.

.

Thanks for asking your question. Your helping me pay my bills, and I

am hopefully helping you lower your repair bill or at least informing

you of the repair needed prior to getting it fixed.

You are about to see our rating system. The rating is how I am paid.

No rating and I am not paid. Neutral or Negative rating and I am not paid.

I am only paid once you rate OK or GOOD or EXCELLENT SERVICE.

For some customers there is not a rating, just press ACCEPT then.

Please if you need to follow up, only press REPLY TO EXPERT.

You can also reply after rating if needed. I also ask that you do reply

and state which service you wanted to select because there has been

a problem with the rating system.

Thanks Chris

I am having trouble finding the vacuum reservoir on your older vehicle due to poor diagrams in 92. I know it has one and it is most likely on the passenger side of the engine compartment and probably looks like a 1 Quart metal green bean can about 3 inches in diameter. The black line from the intake feeds this circuit.