AC pressure switches, blower resistor, grounds, or AC control unit?

[susurban]

Sup y'all! Bought my first Chevy ever with it being a '95 C1500 Suburban with about 210K miles! Drives smooth, 5.7 TBI, absolutely love this truck. However I'd like to be more comfortable in it for longer trips that involve more than one stop LOL

So here are the symptoms:

1) AC blows cold for several minutes after driving from a cold start.
2) AC turns hot like if the blend door was switched to heat.
3) Surging blower velocity, sounds full blast then tones down then full blast, and my legs and feet are being blown by the lower vents too, even with the AC fan off and the direction set to upper vents.
4) AC will remain hot throughout the rest of the ride until the truck is shut off for a while and start from cold.
5) Recirculate button always illuminated when engaged/disengaged, AC button always stays unilluminated.

Also I get no cold in the rear vents but I'm guessing that's a separate system entirely so no big deal, it's just usually me usually in the truck.

Number 3 sounds like a blower resistor to me but since I'm getting both legs and feet and I'm losing AC after driving a bit, could it be there is a lot of resistance in the control unit itself sending weird signals to the pressure switches, blower resistor? Pressure switch connector has already been replaced with a pigtail. Could bad grounds itself be causing everything else? My radio works just fine, the dash lights and driver/pass overhead lights work fine too.


Thanks for any help!

 

[kolgeirr]

With that much going on at the same time it's really difficult to narrow it down on a forum.

My hunch is you need a new controller, but there's a few things you can inspect.

I'd start by getting eyes on all three front blend door actuators and seeing if they function properly. The vent mode one is on the right side of the driver's footwell. Temperature one is easiest to see by removing the 12v socket panel/ash tray and glovebox. Recirc door is in the passenger footwell near the firewall, easiest to test by removing the blower motor and watching the door through the hole it leaves.

Go run the AC and see how often the compressor clutch disengages. If it's short cycling it might be time for a recharge. If not, and the under hood lines are cold, go back and check that temperature blend door again.

Blower resistors are cheap, but usually that failure results in some fan speeds not working at all. Also, the max fan setting bypasses the resistor and is a direct wire, at least on my 99. If you get that fan surging in max fan it's probably the controller or the blower motor itself.

 

[pressureangle]

^^ this
Also, bad grounds can cause almost *any* symptom. You can easily test the heat issue by comparing the air temp to the evaporator outlet temp. If the air is hot and the pipe cold, it's your blend door. If the pipe is only slightly cool or warm, you have an A/C issue. There are 3 pressure switches; a too-low switch on the accumulator, a too-high switch on the compressor, and a fan-on-high switch on the condenser behind the grille. If you bypassed the too-low switch, you may still have air in the system, which overheats and shuts down until it cools again- a very common problem. Your condenser should get hot enough to be uncomfortable to hold your hand on (~150*) if it's *very* hot, you have air contamination in the system. Had you said only "it starts cold, then goes hot until it's shut off a while, then cold again" I'd have simply said check for air contamination.

 

[susurban]

Thanks folks, really. I'm gonna be testing this out as soon as I can and will be posting the results!

 

[susurban]

As a double check, where would be the locations for all the grounds of the truck? I wanna check those too in case of any corrosion.

 

[GoToGuy]

Battery neg, short leg to body ( 10 inches) Neg battery to eng block( int. manifold bolt usually)
Rt rear eng comp , right rear eng head to body braided strap.
Same area, body to frame braided strap.
Those are basic eng compartment.
In the service manual there are line drawings with all wiring ground locations. As there not just anywhere, they have specific locations and list what items are and have that ground.