HVAC mode & temp sluggish

[Guest jimmyk]

My '89 temp doesn't always respond to settings. If I 'encourage' the lever from the controller (behind the glove box) it will then move to adjust to match the setting on the touch screen. Second, my HVAC won't change to defrost mode. All other modes will respond to settings on the touch screen.

What should I check first?

[Barney Eaton]

The rod is controlled by a stepping motor in the controller. The diverters are controlled by vacumn.

(1) Check your vacumn source...... look for cracks or disconnected lines. Start at the engine. A cruise that will not engage is an indicator of a major vacumn leak.

(2) Disconnect the rod (behind the glove box) move it by hand, if it is stiff, you may have debris obstructing the door movement. This could be gasket material, leaves, or other crap. Free up the movement and your controller may work fine.

[NCReatta]

You probably need a new controller. I have seen this problem lots this summer. The vacuum lines have never been cracked or broken. It's always the controller.

I have the available. Give me a call at 919 233 1973 if you're interested.

Sent from my mobile device using Forum Runner

[Barney Eaton]

I make the suggestions of things to check, before buying a replacement unit. If you buy a replacement and then find it does not fix your problem, you must then go thru the hassle of trying to return the unit. Most vendors will refund you $$ but will not refund shipping.

Just do a few checks first.

[Ronnie]

I make the suggestions of things to check, before buying a replacement unit. If you buy a replacement and then find it does not fix your problem, you must then go thru the hassle of trying to return the unit. Most vendors will refund you $$ but will not refund shipping.

Just do a few checks first.

I agree with Barney. Swapping out parts without doing proper troubleshooting to pinpoint the problem can get very expensive. It can also cause a lot of frustration if the part fails to solve the problem. Just my 2¢.

[Guest jimmyk]

Where does the vacuum souce enter the interior? When I've disconnected the rod from the temp controller, the rod seems to move easily. But I wil check this again.

[Barney Eaton]

The vacumn line is easy to trace. The main line runs from the top of the engine (at the intake) straight back to the firewall. It is easy to see and repair if needed. When it gets to the firewall there is a black plastic check valve and one line goes to the right and another to the left.

The line on the drivers side loops around to the cruise control(er) the line going to the passanger side is exposed until it get in front of the passanger, where it goes into the interior of the car.

[Guest Richard D]

Is it safe to assume that if your cruise control is working properly that the vacuum that operates the A/C system is also getting good vacuum?

[Guest Mc_Reatta]

No, that's why they used a double check valve there instead of a tee. Either line could leak and not affect the other side.

[padgett]

OK, the HOT/COLD diverter rod is controlled by a small electric stepper motor, it is not vacuum. If the rod moves freely but the stepper motor doesn't (be aware that it is geared down to very slow, 30 seconds MAX HOT to MAX COOL). I have also seen maladjusted ones cram the valve to one side or the other and jam that way.

That said, I just had to replace one this spring and is easier/cheaper to just replace the whole programmer (black box) with a good used one but that did not move the rod at all.