94 Dodge Dakota
Hx: Heating and all interior dash controls seem to work, though no change in air flow when changing from recycle to outside blend of air.

AC problem: No cool interior air what so ever.

Compressor seems to cycle in 10-15 second intervals after freon added. Low pressure side at approx 80 degree ambient air is 25-50psi. Do not have high side guage to test.

Aluminum lines going into firewall from engine side has one ambient temperature and the other *very* cold with outside condensation.

Cab controls all seem to work (fan speeds, direction, blue AC button). As mentioned previously, not much difference in recycle mode with usual cab pressure slight change in other normal operating vehicles.

Tentative thought that freon cycle working correctly at proper pressure but this is a interior cab poor air exchange issue?

Would a blend door failing to open or close cause total lack of AC?

Thanks in advance for any help, suggestions or thoughts.

94DakLover

 

yes also you should check for vac at the dash control on my 89 its the black line

 

Thank you for your quick response.

I am reviewing Haynes on getting to the AC and Heater control assembly.
And will check to see if there is vacum on the black hose this weekend.
(Seems like this is a better initial approach than to try and access the blend air door to verify movement)


Unfortunately I will not know what to do if the black hose shows no vacum.
Might you know of the purpose of the black vacum line in the control assembly and where to trace it back to find the leak source (firewall, etc.).

Thanks again for your time and input.
94DakLover

 

a bit of info for you, in case you didn't know...the source of vacuum for the heat/ac controls enters the cab where the coolant lines for the heater core enter on the firewall. if there is a vacuum leak that would be the first and easiest place to get to.

 

It could be the actuator or the door itself. Check the actuator in the middle above the hump. If that moves. Then on to the other.

 

Thank you all for the info! It is *very* much appreciated.

One point of major confusion on my part is Haynes shows a cable and a "blend-air door crank" in their picture of the AC/heater control assembly. Implying it is a mechanical throw to the blend door? Not electrical with an actuator???

Another point of confusion is the purpose of the vacum in the AC\Heater control assembly? I could see that it could be used in the mode(directional) doors?

Thanks again for everyones patience. I am struggling with the understanding how the control module works...

94DakLover

 

Mine also wasn't cooling properly, had proper levels of freon & what not. The heater control valve wasn't closing, allowing hot water to keep circulating through the system. Spliced in a gate valve into the hot water line & it cools like a champ.

 

I thought you boys up north were tired of cold. What you need A/C for anyways. Enjoy the heat.

 

NorDakota,

Wanted to thank you for the idea of installing manual gate valve(s)
on the heater lines on the engine side of the firewall!!!!

After determining that the AC/heating control assembly buttons/switch/lever
all seems to be functional. And the freon levels and freon closed system loop
seems functional. Noticed that the heater lines before entering the firewall
on the engine side were rather scorching hot even when the ac has been running
for 10-15 minutes. (The water pump and thermostat seem to be functional as the
dash coolant guage does not show overheating).

Do not know where the the heater control valve is located or how to test if it
is shutting properly. Makes sense that it would close when the blue AC button
on the AC/Heater control assembly is activated. Why design a cooling system
that must overcome added heat?

Is there an electrical or vacum signal to the heater control valve that I should check?
Where is that dang heater control valve?

Even if I can't find/test the heater control valve a couple of gate valves on the
inlet and outlet of the heater lines on the engine side of the firewall would
just need opened/closed in the fall/spring, twice a year. I could live with that!

Any rec. on type of valves? Obviously to withstand the heat and pressure of the antifreeze/coolant specs. Brass? Hose clamps due to pressure?

Thanks again for everyones input

94DakLover

 

The heater mix door is on the passenger side. Lay on your back and look up. You'll see the actuator. The one that controls the def/dash is by your right foot above the hump.