1989 Lincoln Town Car AC System Question

Bill,
I have a 1989 Lincoln Town Car Signature Series.
I’m told that I need a new Diverter Valve for my Air System. The Heat and AC work fine individually, but I can only use one or the other! If it’s hooked up and plugged in, the AC works strong, but can’t be controlled and I have no heat. It’s either on all the way or I have to turn it off. Vice Versa, if it’s unplugged, the heat works strong (but I do not have AC access), but again I can’t control the temp. It’s either top heat or I have to turn it off!
If it is the Diverter Valve, how much should it cost to replace?
Thank for your time and advice.
Michael
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Greetings Michael –
After reading your post several times it sounds to me that your hvac control sensor also known as “sniffer sensor” (above the glove box under the dash pad) has failed in the cold a/c position. When the Servo unit vacuum (under the dash) is unplugged the system defaults to the maximum heat position. These sensors are available new.
Automatic climate control systems however should be diagnosed on scene as per the maintenance manual to positively identify the failed part. The above diagnosis is based on past experience and on the content of your email.
Sincerely,
Bill