HVAC help

[WillB]

Hoping for some HVAC help in my 99. First is the A/C. I turned it on to check if it worked. Was told by the previous owner that the switch didn't and the way got it to work was jumping it at the relay under the hood. I got a different HVAC control panel and put the relay back in and tried the AC tonight. I noticed the clutch didnt kick in when I turned the A/C on. I checked and replaced the fuse in the compartment in the cab with no success. Swapped relays with the starter relay under the hood and it still didnt work. Not sure what to test next there.

Next is my vents. It seemed I was only getting air out the defrost and vents on the dash. I figured that it was the blend door actuator by the accelerator pedal. Changed it out and it didnt seem to change. Should I be able to see the white splined piece moving on it? I dont seem to see it move as I change from floor to defrost etc.

 

[someotherguy]

You could have several issues going on. My initial suspect would be, if the previous owner wasn't simply BS'ing you, is that the controls are bad or the fan switch in the controls is bad (you can replace that switch separately, pretty cheap.) The later style interior A/C controls are notorious for being weak. If the other controls you tried were used, possible they're bad as well.

Next up, if the A/C hasn't been run in quite a while, it may have leaked out enough refrigerant charge that the low pressure switch is keeping the compressor from engaging. Your HT6 compressor is known as the "belly leaker" because they often leak at the seam in the middle where the two case halves meet. If it's oily and grimy there, it's leaking. You can momentarily jump the low pressure switch (it's the one on the accumulator "drier") to see if the compressor clutch will engage. Don't run it like that, though. BTW those switches can go bad, but the overwhelmingly far more likely scenario is low refrigerant.

Vent position is one of the common failures of the new style controls. Especially if someone has had the radio out for any reason, such as swapping to an aftermarket piece, or the radio got stolen and the wires were left hanging. As you've noticed, the circuit board on the A/C controls is exposed, making it easy to get shorted out from anything falling on it from above, like cut radio wires, or the antenna connector. Other causes for vent position failure include the linkages gumming up or falling off, the flaps breaking where they pivot, etc. and -sometimes- the actuator itself, but you would have noticed linkage or flap problems while you were down there.

My advice would be start with the fan switch - or new controls if you don't mind spending the bucks - see if you can get the controls coming on and fan speeds working first. Next, check vent position which hopefully will be solved by the new controls. Then, the low pressure switch jump to see if you can get the compressor engaging. If yes, then follow up with an A/C pro that will pull a vacuum and see if it will hold, or if the leak is bad enough you need to repair the system (likely the compressor) before charging it up.

EDIT - I may have misread you a little bit, if the fan speed is working from the switch then obviously you can ignore that part.

Richard

 

[WillB]

The fan works fine on all speeds. I will try to add some refrigerant to the system to see if it has leaked out and tripped the low pressure switch.

 

[someotherguy]

I would not add any refrigerant unless you have a set of gauges and know how to read them. You could jumper the low pressure switch as I suggested and see if that has an effect.

Richard

 

[WillB]

So I got some more time to mess with this. The only way I can get the compressor to kick on is if I run a jumper between where the 86 and 30 pins go at the fuse/relay block under the hood. Bypassing the low pressure switch did nothing. I took a test light and checked both wires at the compressor and had no power. I switched relays with the starter relay and still no change.