1986 Ford Crown Victoria Rapid Acceleration Relay? Or vacuu

Yes, have traced and checked every vac line I could find. Have checked under the hood and under the dash, problem is constant - under load, accelerate and the air goes off, comes back on when speed is maintained or road levels (i.E, no load on engine). Driving me crazy

Thanks for the advice. Found the check valve, ordered and picked up from Ford. Installed (along with the check valve on the engine side of firewall off what appears to be a control block - a total of four lines run off this block two large lines, the line the check valve was on and the bottom one a small plastic line), NO CHANGE, problem still exists.

Checked all vacuum lines again - can't find any problem with lines, connectors. Tried spraying carburator cleaner along lines also - no indication of any leaks.

I did discover another issue - the Heater won't work. Put the selector on FLOOR and everything shuts off. Seems to work fine on HI/LO, MIX and Defroster. When the a/c shuts down when accelerating -
The MAX Blower shuts down
A door closes (one behind the Glove Box)
The a/c continues blowing cold air for a few seconds
and then HOT air is blown out?

Driving me crazy!

Thanks, will go over everything again. It sounds like something simple, but it's hidding really well.

I checked the line going to the blower door, disconnected the vacuum line, accelerated, the line LOST Vacuum! Checked the line, goes to a "t" then splits off, one line to the actuator housing for the Climate Control Switch the other is "buried" looks like it goes up and through the firewall? Could it be the Climate Control Switch? There are eight vacuum lines going into this switch - and the heater doesn't work - maybe the entire switch is bad?

Sorry for the delay in getting back to you, I have worked on this every day and it only gets worse.

Local dealer checked vacuum under the hood and says everything in front of firewall is Ok. Removed each of the 15 or so vacuum lines under the dash, checked lines for damage. Further investigation has turned up that the same thing happens when the Climate Control Switch in set on "Vent", i.E, the cool vent air becomes hot on acceleration, returns to normal vent air when I let off the gas.

On both A/C or vent the same thing happens and the system DEFAULTS to putting all air flow to the windshield - which the dealer says is the default if any problem occurs with the heater, a/c, ect.

Heater DOES NOT WORK AT ALL. When the Climate Control Lever is moved from off all the way across to defrost, doors open and close, air changes directions, everything seems to work - EXCEPT - when set to FLOOR (heater) its the same as setting to "OFF", everything IMMEDIATELY STOPS. No air flow anywhere, including the windshield. Removed switch and cleaned all contacts, including the "strips" inside the switch, re-lubed and put back together, the ball bearing is in place and the switch does work.
Wiring is all in place - is it possible that there is an "in-line" circuit breaker for the heater, that is NOT mentiioned in the owners manual? Have also checked all fuses, the heater, the a/c and other components on the same fuse - all work except heater door? Heater blower?

I am not a mechanic, don't know how vacuum systems work, don't know how to locate the "door" for the heater - appears that this "door" is not working at all. Assuming the same blower is used for the heater and/or a/c, if so, the blower works.

Really don't have the money to take the car to the dealer and let them have for one or two days - Service Advisors admitted they didn't know what was wrong - 86' crown vic not on their computers - have to lookup in books? How is mechanic going to determine what is wrong? And, can I do the same thing to find problem, or just give up?

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