probably another dumb question, when you say mode switch, do you mean the mode selectors with the temp dial, speed (1-4) and mode selector?

there is a slow hiss noise when switching modes from the one to another. not sure if thats normal.

 

The mode switch is the dial that you turn to select where you want the airflow to come out.


The hiss noise between modes is normal, but it should stop very shortly after you make the selection. When you change selections, some of the actuators need to vent the vacuum that was applied to them.

 

ok did as you said, i did not disconnect the black line behind the mode switch i took the whole thing off, and plugged in the tip of the vacuum pump into it. it held at 20 for over 25 minutes until i released the vacuum pressure. should i test the other lines (blue red etc) or have we ruled it being the mode switch where its leaking?
also if it is the mode switch, do i need to replace the entire hvac control unit or just a specific part? and part number if available

 

Checking each individual line at the vacuum line connector will double check the lines and the actuators, good idea. Each one should hold vacuum. If you find one that doesn't, post what color it is. Then we can do one more test to make sure the mode switch is faulty. Once we figure out where the problem is, then we can get part numbers

 

i did each tests for all colors for 10 minutes, yellow and brown were the only ones that did not pass. did it 2 times. same results...lost 4-5 after 10 minutes.

what should i look at next?

 

Losing 4 or 5 inches of vacuum after 10 minutes is not real serious, and probably not the root cause. If it loses vacuum rapidly going through the mode switch, that's most likely the problem.


Yellow goes to the mode valve actuator. It's a 2 position actuator above the gas pedal. There are two actuators there, and it's the top one. The brown also goes to it, and to the slave actuator. That one is on top of the heater case and involves taking the dash apart to get to it. If you apply vacuum to the yellow line, and kink the brown off at the slave, that will tell which one is leaking. Might not hurt to try to narrow it down.

 

thatll most likely be another day testing the brown and yellow , you also mentioned testing the mode switch, how should i go about doing that?

 

Connect the vacuum pump to the port that the black line connects to on the mode switch. Select BLEND and apply vacuum, it must hold. It not, the mode switch is faulty.

 

vacuum fizzes right out of it, wont even hold. vacuum line is nice and snug

and just clarifying when you say bi-level, you mean floor and vent mode which is has a line connecting it to ac and max ac

 

Floor and windshield on the icon. If the black port does not hold, you found the problem.