How do I check vacuum system for 92 Cadillac devill climate control system?

It is a known issue

92 Deville climate control not coming on ' Cadillac Owners ...

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Jan. 10, 2013 - Hello, I have a 92 cadillac deville 4.9L In general it runs fine but recently we ran into a problem. The problem is the climate control panel ... 1992 Deville Heater/Climate Control Issues ' Cadillac Owners ...
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Bad heater core , I had the same problem , and replaced it and now I have heat

Ahh 87. Nice car.. Well since you have an Electric issue, I can't tell you how to check for shorts and other items BUT you can get a Vacuum tee and tie into a working Vacuum line and add a small 1/4 inch vacuum line to the Heater control valve on the passenger side engine heater hose and that will start sending the hot water/coolant into the heater core, I hope your blower works you would have heat, I really never like that auto Climate systems.. But that will give you some heat and give you more time to get the dash to work.. BCB...

to john cannon the code f means body code like air conditioner,vehicle speed sensor park switch,climate control etc.

Hello williamcole7: My name is Roger and I will help you. The code 888 is a test code. This tests the L e d's of the dash cluster. All segments must light so you can read all numbers. The 70 code means the system is ready and able to function. The ff code is a current BCM code and is happening at the moment. The f 40 code is a BCM history code and means it was a stored problem or something that has happened. The f 40 code is for a air mix door problem. THe BCM would set this if you had an A/C problem. The E 48 code deals with the EGR system fault. I would check for a vacuum leak at the EGR solenoid. The hose is prone to deterioration do to heat from the engine. Code E52 deal with loss of voltage. A dead battery or a disconnected battery cable will always set this code. None of these codes will keep the car from running.The repair schematics are to extensive to send in a reply. Should you need further help ao assistance I will be glad to help. Please rate the answer. Thank You for using Fix Ya. Roger

I would say either blend door issues or a vacuum control valve, heater control valve or a vacuum hose to the heater system is leaking. I would start to suggest. You are correct in checking the blend door. A computer scan should tell you what temp the climate control thinks it is in the passenger compartment. It may be a thermostat problem giving the climate control a false reading. Your blend door is controlled by a servo motor under the dash. You can remove the servo and watch to see if it moves when you change the temp setting from heat to cool. Also, you should be able to manually move the door to the heat position and see if you get heat.

F40 = Air mix door problem for heat and A/C system.

Check for a fuse that indicates radio and replace it if it's burnt through or melted or discolored. The Buicks have dash controls that require expensive repairs sometimes to get the temperature controls to work so some people jump around the controls by installing a separate toggle switch that directly turns the AC unit off and on for 92 through 94 Buicks. Any AC shop can install the bypass wires.

is the fan motor working at full speed
check for blocked cabin air filter
the vacuum only works the vent controls and as you can feel the changes of the vents , it is not vacuum

there are two separate actuators for the rear system. one controls temperature and the other controls vents from head to feet. mine problem was the later. that acutuator for esv 2003 is 89018365. it is located just below third seat cup holder passenger side and can be replaced simply by removing cup holder. triangular shaped part with wire harness.