ac/heater

On 3/1/2012 1:01 PM, HL B123 wrote:

On Ford trucks (and most other vehicles), the air direction doors in the
HVAC system are controlled by vacuum. When there is no vacuum, the doors
are moved by springs to their default settings, which is recirculated
air out the defrost vents. This tells you you've lost the vacuum supply
to your controls.

The first place to start looking is probably at the vacuum lines in the
engine compartment. Not all vehicles are the same, but it is likely if
you find the large line coming off of the brake vacuum booster and
follow it, you'll find a junction block with a large line going to the
intake manifold (that's your vacuum source), and one or more small lines
for vacuum for other functions. One of those lines will go through the
firewall into the cab to the heater controls.

Check all those lines to make sure they are attached and not cracked,
degraded or leaking. If everything looks good, then you're going to have
to find the supply line under the dash and check it for a good vacuum
supply, make sure nothing has come detached from the heater control
panel, etc.

--
David Chamberlain

The AC works on every setting EXCEPT floor or panel, but when both floor and
panel are selected for a mixed delivery option, then the AC does work. Any
Mixed Setting and Defrost will invoke the AC. You cannot select Floor or
Panel to get AC.

If you are saying that you cannot get air to come out anyplace but Defrost,
then that is a problem with the vacuum system. On my truck, there is a check
valve in the tiny space between the battery and the firewall. The hose on
one of the connections --the valve forms a T -- had a hole burned into it
allowing the vacuum to leak, and the heater control defaults to Defrost when
that happens.

Thank you to both David and Jeff for your prompt and right on responses
to my ac problems.I found and traced the vacuum line to where it should
have entered the firewall right behind the battery .The hose was bad on
the end,fixed it and I now have air at all the positions .  thanks again
hlb

Glad to help. I had the same problem, and asked here how to fix it. I pretty
much got the answer I gave you.