Cheapo Tow Rig project

I do still have some issues with my AC, hoping someone can point me in the right direction. It’s still doing the thing where it blows nice and cool, but then it stops blowing as hard. I can turn it up to 5 and hear the fan speed increase, but the air flow barely changes. If I turn the compressor off for just a few minutes it stays cold and then begins to warm up and blow harder. I’m pretty certain the Evap coil is freezing up blocking the air flow and then thawing when I cut the air off. Why is this? It doesn’t appear to have any leaks. I plan to put gauges on it again this week and confirm it hasn’t leaked down, but I checked for leaks with soapy water and saw none. We had good vacuum on it before charging. It was doing this before the compressor went out. I thought this wouldn’t be an issue anymore.

@a_kelley @Croatan_Kid any suggestions?
 
Same thing this other truck the same vintage was doing.. yes it's definitely freezing up.

Are you sure it's not under charged?

Also did you flush evaporator and condenser, replace orifice & drier?
 
there may be a panel under the dash that conceals a HVAC cabin filter door.

not all trucks of that vintage had them, years ago i got nailed on a CSI because i didn’t change one i didn’t know was there.

Also, the evaporator case is a good place for dust, grass, chaff anything construction related to get drawn in and restrict air flow, it’s drawn in from the cowl vent behind the hood edge. i don’t remember if you can see the core by removing the cowl cover, but it’s worth a shot to check. gotta pull the wiper arms off and some hood weather stripping.
 
I did not do a flush, I probably should have but I replaced everything but the Evap coil. New dryer, condenser, compressor and orifice tube.

From my research, it seems 04 did not have a cabin filter. 01-03 did, and 05-07 did for that body style but not 05??

I originally thought it was a blend door problem. But it’s clear that it’s thawing out when I turn it off. I will get my friend to put gauges on it this week after I get my camper off and I will also investigate the cowl I take and around the box for the blower motor.
 
77GreenMachine said:
So I just came back from a 4 day trip to Potts Mountain with my whole family. We took the YJ, the camper, and lots of gear. No idea what the weight was but the truck handled it all great. I knew the camper would hurt my mileage but it was worse than I thought at 7.5mpg. I didn’t need fuel on the way back so I haven’t checked the return trip but I know it was a bit better coming back.
That is some sucky MPG, but at 5-7 trips a year I’m still ahead with no payments!

Having the camper is a game changer! My wife loved it, it made everything so much easier. We were even able to put my son down for a midday nap in the AC.
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This mileage makes me feel better about my big block now. Glad the camper worked out for you!
 
k5-1402 said:
This mileage makes me feel better about my big block now. Glad the camper worked out for you!
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It has certainly slowed me down a little, but I’ll get there when I get there and I’ll be comfy when I do! I can still run 70, but it don’t take much of a hill to make me drop a gear.
 
Is the compressor cycling? If it isn't, you could have a bad low pressure switch. Once the low side pressure gets too low, it'll get too cold and freeze up the evaporator core.

It's the switch that screws on to the drier. Sometimes they crap out and sometimes the wiring pigtail to them goes bad. You can pull it off and check for continuity with a multimeter, but the switches are pretty cheap.

The evap core could definitely be dirty. You won't be able to see it or clean it unless you pull the HVAC box. I also haven't seen any 03s that had cabin air filters, but maybe they do...who knows? If yours does have them, you can slide them out and see most of the evap core.

I guess there's also a possibility that the orifice tube has a partial restriction, but I'd save that for last since you obviously have to evac the system again.
 
77GreenMachine said:
I did not do a flush, I probably should have but I replaced everything but the Evap coil. New dryer, condenser, compressor and orifice tube.

From my research, it seems 04 did not have a cabin filter. 01-03 did, and 05-07 did for that body style but not 05??

I originally thought it was a blend door problem. But it’s clear that it’s thawing out when I turn it off. I will get my friend to put gauges on it this week after I get my camper off and I will also investigate the cowl I take and around the box for the blower motor.
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On our 01, it had several interior and exterior temp sensors. One was causing the compressor to not run.

Long story short, hooked a toggle switch on the dash in place of the low pressure switch. Close the switch and compressor runs. Open the switch compressor doesn’t.

The factory ac computer crap controls the compressor cycling and it reads the interior and exterior temps to know how often to cycle.

Not sure that is your issue, just another thing with these generations.

On my 04, when the blend doors would act stupid, I’d pull the hvac fuses and relay, and follow the factory resetting procedure. This would fix the blend doors not functioning correctly for a month or so.

When the reset is done correctly, it will cycle all the doors to find their position again with key on, engine off.
 
Brain storming and trying to trouble shoot why my AC is freezing up, I realized I may not have enough refrigerant. The sticker under the hood was not legible. I got some conflicting info online and wound up going with 1.8lbs
I’m second guessing that now, does anyone here have one of these trucks that can read the sticker? Or find some info online that is 100% confirmed to be the right amount?
 
My Duramax calls for 1.8, but I believe my 99 1500 says 1.6. I'd say 1.6 as well.

Did you ever check the low pressure switch on the drier? What kinda shape is your fan clutch in?

It may have even flushed some junk out and stopped up the orifice tube again.
 
Croatan_Kid said:
My Duramax calls for 1.8, but I believe my 99 1500 says 1.6. I'd say 1.6 as well.

Did you ever check the low pressure switch on the drier? What kinda shape is your fan clutch in?

It may have even flushed some junk out and stopped up the orifice tube again.
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Just pulled it off and it does have continuity.

If the fan clutch was failing wouldn’t the truck run a little hot? As of right now with the truck cold it does have plenty of resistance. Guess I need to check it hot.
 
77GreenMachine said:
Just pulled it off and it does have continuity.

If the fan clutch was failing wouldn’t the truck run a little hot? As of right now with the truck cold it does have plenty of resistance. Guess I need to check it hot.
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It shouldn't have much resistance when cold, it should free spin to allow the truck to warm up faster and as it gets hotter it should lock up tighter.
 
Stuntman Autoworks said:
It shouldn't have much resistance when cold, it should free spin to allow the truck to warm up faster and as it gets hotter it should lock up tighter.
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yes except for that when cold the silicone fluid that's in the clutch is settled out, instead of being distributed around, which is why on a cold start the fan pulls really hard for a minute before it gets to how it's supposed to be. Hot doesn't necessarily mean it'll lock up hard - it relies on the hot air acting on the thermospring to engage it. Best test I've come up with for a mech fan clutch, is if when revved hot starts pulling lots of air. There is an actual temperature based test that can be performed, but I've not seen many fan clutches go out (compared to radiators stopped up).. furthermore, the issue at hand is that the low side is getting too cold/too low pressure, not that it is not cooling, so the problem isn't on the hot side...
 
Fan still has plenty of resistance hot. I’m certain the fan is fine. I hear it cycling as needed on hot days. If I stop at a store and cut it off, then get back in, the fan is pulling hard at first till I get moving down the road just a bit.

Should the low pressure switch have continuity if I have it removed? Seems like it should be open if there’s no pressure on it?

I’m convinced the evap coil is super dirty, and that sucks a big one cause it’s not easy to remove and clean. There’s an option to cut the dash up in a way that won’t be seen, but I’m not crazy about that. It also has a high risk of puncturing the coil. AC works great long as I turn it on and off from time to time.
 
With pressure less than like 20ish, the low side switch will be closed. It's normal position is open to allow the compressor to run.
 
Croatan_Kid said:
With pressure less than like 20ish, the low side switch will be closed. It's normal position is open to allow the compressor to run.
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So it is working like it’s supposed to then?
 
Sounds like it...unless I got that ass backwards, but I'm pretty sure I'm correct. :D
 
So how bad is it to remove the dash to get to the evap? I’m assuming I have to drain the system so I can disconnect the air box as well?
 
Also, I’ve had a CEL for some time. I was getting a P0141 code for bank 1 sensor 2. On the way to Choccolocco I would Clear it and it’d come right back. But yesterday I got my hands on an Edge HT2 programmer. I cleared the code with it and went on like a 10 mile drive with no light. Then I decided to check the connections on that o2 sensor, only to discover it had come completely unplugged! I plugged it back up and started the truck, still no CEL but I didn’t drive it.
I’m wondering if that plug was coming lose, throwing the code as made connection and lost it with movement up until it finally came totally unplugged. Who knows, time will tell. I don’t think I’ve driven it enough to see if it will come back.

Put the Edge on a Tow Tune and will be heading to a Harlan next Thursday. I don’t expect it to make a great difference but we will see.
 
If someone has done these dashes before, they can be out in 30 minutes. If you haven't, it'd be a several hour endeavor. The guy that did mine had the dash out before I got back home from dropping the truck off at his place.

You'd have to evac the AC system again and drain some coolant. The heater core is in there with the evap core. If I was going to pull the dash, I'd probably put in a new evap and heater core just to be done with it. AC Delco, of course, because I wouldn't want to do it again. I'd probably replace the top door actuator while I was in there too since you can't really get to it with the dash in place.

Sounds fun, right? :D
 
Alright so I took the truck to my buddy’s house and we put gages in it, everything read good. But then when you rev the truck just over 2k as if you were riding down the road the pressure drops and it begins to freeze if the air is on low. On wide open it looks good.

I was able to remove the blower motor and stick my phone in there and made a video to look at the evap coil. It really doesn’t look bad surprisingly. The pressure got down to 22, not enough to trip the low pressure switch.

So we had originally put 1.8lbs (calls for 1.6) in it so we wondered if it was over filled and wouldn’t let the pressure drop enough. Figured that was a very slim chance since it was only slightly over filled but trying to rule everything out. We wound up pulling it back down and refilling it correctly. While we were pulling it down, we started the truck to see if the compressor would kick off. It never did, all the way down to empty the compressor continued to run, so at this point I’m pretty sure the low pressure switch is bad even though it’s brand new and shows continuity when unplugged. It’s only $15 so I’m going to replace it and go from there.


Open to any other thoughts. This problem is extremely aggravating and is literally keeping me up at night and distracted from work lol.
 
Sometimes the wiring to the lower pressure switch can get janky. I'd check the continuity on the pigtail. I'd probably check any relays associated with it to make sure they aren't stuck. The high and low pressure switches are pretty much what controls the compressor clutch. Does the clutch release when you turn off the AC?
 
Croatan_Kid said:
Sometimes the wiring to the lower pressure switch can get janky. I'd check the continuity on the pigtail. I'd probably check any relays associated with it to make sure they aren't stuck. The high and low pressure switches are pretty much what controls the compressor clutch. Does the clutch release when you turn off the AC?
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Yes the AC will cut off when I cut it off. I didn’t think about checking continuity on the plug. I’ll check it tomorrow. I’ll also swap some relays around.
I did mean to mention that there is 2 plugs. The other one will not actually reach the switch in the accumulator, and is slightly different, but why is this switch here? See index finger.
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