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Discussion Starter · #1 ·
I think I have 2 cold weather problems, an AC that comes on no matter what the temperature setting, in register mode, or split floor and register, but it does not come on in the floor mode setting, with the temperature set to hot. The compressor cycles in those 2 modes, and the evap surge tank is very cold. The blend door seems to be working OK. Could it just be the AC on/off button is stuck ON?

I think the other problem is that the heater core needs flushing because the driver side heater hose at the firewall is hot, but the passenger side one is not.

Bit I think my first problem will be to get the AC not to come on when the temperature is set to max heat and it's 30F outside. Could it be related to this connector that seems to go no where coming out of the wire loom by the evaporator surge tank?
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Welcome, vehicle info is a big help.

When the AC button is in the off position, the AC should only come on when defrost is selected.

You need to find out if the AC relay is operating when your in the other positions.
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Find the AC relay in the underhood fuse panel, place 2 fingers on it and have someone cycle through the different mode switches, write down the positions that you feel the relay click.

Edit.

And, I don't follow the statement about a driver's side and a passenger side heater core, most vehicles only have one on the passenger side.
 

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the coolant heater hoses, when the engine is hot both hoses are hot correct ... now back in the old days on my 2000 silverado GM put dirty water in it .. also my 1996 Impala .. I flushed out the heater core and I put distilled water 35% and 65% dexcool ...........................my vehicles are heater very hot air temps 145F... and also when you replace and flush the coolant full up the coolant then start the engine ,, remove the coolant cap .. rev the engine a few time when the engine temp is at 190F . air will bubble out of the coolant,,,,,,,,,,, plastic tank port cap.
 

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2000 Silverado Z71 4x4 5.3L 480k+ miles w/ GM rebuilt motor and trans
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I think I have 2 cold weather problems, an AC that comes on no matter what the temperature setting, in register mode, or split floor and register, but it does not come on in the floor mode setting, with the temperature set to hot. The compressor cycles in those 2 modes, and the evap surge tank is very cold. The blend door seems to be working OK. Could it just be the AC on/off button is stuck ON?

I think the other problem is that the heater core needs flushing because the driver side heater hose at the firewall is hot, but the passenger side one is not.

Bit I think my first problem will be to get the AC not to come on when the temperature is set to max heat and it's 30F outside. Could it be related to this connector that seems to go no where coming out of the wire loom by the evaporator surge tank? View attachment 171279
I have the same connector to nowhere. I think it's probably for some fancy thing you and I don't have.
 

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2000 Silverado Z71 4x4 5.3L 480k+ miles w/ GM rebuilt motor and trans
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Also, what are you driving? I might have missed it, but can't find the info.
 

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2000 Silverado Z71 4x4 5.3L 480k+ miles w/ GM rebuilt motor and trans
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And, I don't follow the statement about a driver's side and a passenger side heater core, most vehicles only have one on the passenger side.
I think they're just differentiating which one is hot instead of saying the arbitrary "left" or "right". Either way, a complete loop is not present.
 

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Discussion Starter · #7 ·
This is about my Sister's Silverado. See pick below, it is in outstanding condition except for the heater situation. It's a 4X4, V8. RayVoy, I will do the heater relay thing as you suggest. Thanks for that info, I was not aware of the AC relay under the hood. Also, I can pull that relay out temporarily just to see how much heat the heater core can produce in register mode without the AC coming on. Also I said heater hose, not heater core. I need to do the core flush, hopefully after I fix the AC coming on at the max. hot temperature setting. I would think that just having the temp. set at max heat would also turn off the AC. Yes I know the AC does come on in defrost mode as well, regardless of temp setting, to dry the defrost air.
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Is the DexCool a red color? Because that's the color of what is in her system. and it is up to level in top tank, but I will try reving the engine with the thermostat open and that cap off, to see if I get any air bubbling out. Thanks for that J-Cat.
 

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Dexcool is orange.
I was going to suggest a quick fix is to pull the AC relay; but if you live in a wet area, it is needed to dry the inside of the vehicle when defrost is on.
 

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dexcool is pink when the dexcool is over 5 yrs and tap water is in the coolant the coolant is red . I use distilled water and I remove the coolant 4 yrs .. when I look at it on the old and the new it looks the same color.
tap water creates chemicals and then the coolant breaks down , tap water creates acid to wear out the metal.
tap water has organics in it and the heater core radiator goops up the core ports.
I had to replace my 1996 Impala radiator . OEM .. the driver side plastic tank had a crack .. replaced it and that 20 yr old radiator looks like the new radiator .. aluminum ports looks like new, shinny ...
 

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Discussion Starter · #10 ·
J-Cat, The original owners manual says you can use "drinking" water. But the people who wrote the owners manual weren't chemists, so I'll use distilled water and DexCool per your recommendation. Distilled water is pretty cheap, at least it was last year, I haven't checked lately:)

I did nothing today, it rained all day, and my Sister doesn't want the truck to get wet.:rolleyes:
 

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gm also used tap water mixed with coolant on all there vehicles back in the day. they dont care, it will last longer than the warranty.... well then they formulated dexcool and the early stuff just ate away at gaskets creating all kinds of problems.

yeah you want to use distilled water with concentrate or just use premixed stuff.

I see the picture of the truck and I know it's a 4x4 but I still have no idea what it is.
 

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‘01 Silverado 2500HD 8.1/Allison 5sp xcab long bed
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99-‘02 Silverado. The headlights are a giveaway. They changed in 2003.
 

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Yeah I'm no expert on those trucks whatsoever and I cant tell what it is at all. if the extra little bit of information was provided there might be some more reaponses.
 

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Discussion Starter · #14 ·
Sorry, I described it at my profile and showcase I thought. It's a 2001 Silverado, 1500, V8, 4X4. Zero modifications, totally stock, one owner, bought new, garage kept, by a pretty sister who is anal about keeping it clean inside and out, and she even cleans under the hood!
 

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That's aweaome man I bet it's in great condition! good for her! I bet this is really aggravating.

I dont have a whole lot of experience with this but I know people will flush out the heater core with a garden hose and I have also heard of people using vinagar to remove built up scale and such that comes from using regular or hard tap water. I have not done either of these things.

But I wouldn't think that is the problem and I'm sorry I dont really have a solution.
 

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J-Cat, The original owners manual says you can use "drinking" water. But the people who wrote the owners manual weren't chemists, so I'll use distilled water and DexCool per your recommendation. Distilled water is pretty cheap, at least it was last year, I haven't checked lately:)

I did nothing today, it rained all day, and my Sister doesn't want the truck to get wet.:rolleyes:
I used distilled water decades ago with the anitfreeze ..my 1996 Impala , GM used dirty water I had to flush out the antifreeze , the heater core was blocked up .. new 1 year old ..now I had no dirt in my antifreeze Impala..25 yrs old still working ..
I replaced my drinking water pipes in my house 30YRS. town uses corrosion chemicals and the tap water has sodium [ROCK SALT] ......................HAD copper pipes, , builder put M spec I installed L copper spec twice as thick ...I used silver solder ..
 

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Discussion Starter · #17 ·
Here is what I found out today. Yes the AC being on at all temperature settings in the register only and register/floor split mode was part of the problem. To turn the A/C off all you have to do is unplug the connector shown in my picture above, on the AC accumulator tank. It's the lower connector that is shown plugged into the accumulator in the picture. If unplugged, the compressor will not come on. My inexpensive partial fix will be to unplug that connector for the winter. While it didn't solve the whole problem, the register temperature is now warm (~75F), but not hot like it should be. Before it was ice cold with the A/C clutch cycling on and off. So tomorrow I will do the heater core flush, with some coolant flush that I bought at the auto store. ~ $6.
 

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Here is what I found out today. Yes the AC being on at all temperature settings in the register only and register/floor split mode was part of the problem. To turn the A/C off all you have to do is unplug the connector shown in my picture above, on the AC accumulator tank. It's the lower connector that is shown plugged into the accumulator in the picture. If unplugged, the compressor will not come on. My inexpensive partial fix will be to unplug that connector for the winter. While it didn't solve the whole problem, the register temperature is now warm (~75F), but not hot like it should be. Before it was ice cold with the A/C clutch cycling on and off. So tomorrow I will do the heater core flush, with some coolant flush that I bought at the auto store. ~ $6.
that electrical plug is not connected .. probably the hood lamp ....I did the hood lamp plug pulled it off ...many had failures that the lamp stayed on...the ac controller could keep the ac compressor on ..pull the compressor clutch electrical plug ...
 

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Discussion Starter · #20 ·
OK, I got a lot done yesterday. I parked the truck with the front downhill slightly, such that the heater coolant entrance and exit were at the highest spot in the cooling system. Then I took both hoses off after labeling the driver side hose as the entrance (based on it being hotter). Then I removed both hoses at the firewall. Not easy to compress those clamps, long needle-nose pliers didn't work, not enough leverage. Had to use a large vice grip pliers. Then I just keep the hoses up high enough so that no system coolant ran out, not hard to do that. I have an advantage I guess that I plumed my house with a hot water faucet outside my basement garage. Then using hot water I back flushed the heater core using an inexpensive hose nozzle with a threaded ends at a local hardware store.

Then I put a full 22 oz bottle of Radiator Flush & Cleaner into the heater, filling it with hot water, and let it sit for an hour. Note that at this time I have not drained the system coolant. After an hour I forward flushed the heater, which was the opposite direction of the first flush. I captured what came out in a 5 gallon bucket, and there was not that much debris in it, just a small amount of rubber particles. But I ran a lot of hot water through it in both directions.

Then I put it back together with just the hot tap water in the heater, with the system coolant still in place. I was skeptical that I had made any difference, but I was wrong. It now puts out tons of heat! I put 2 stem thermometers in the left and center register, and both registers felt hot, and took the thermometers to their upper limit of 120F degrees! What a difference! I will add maybe half a quart of concentrated coolant, to offset the tap water that was in the heater. If I eventually replace the coolant, I will use distilled water as suggested.

I did not want to lay on my back under the truck in this cold weather, to drain all the coolant, which obviously was not necessary, given the response of the heater to what I did. Total cost of repair, $6 for the flush fluid, and $3 for the hose nozzle with a hose thread on both ends. Caution, don't use full hose pressure on the heater, it's not designed for the 60 psi house water pressure that I have. Just use the the nozzle to gently run hot water through the heater continuously for maybe 5 gallons, or one minute, that's all I did.
 
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