I am stumped... 2006 GMC truck

[tbirdtbird]

I’d still like to have pressures at 1800 as described.
You can easily see where the OT is in the piping.
At 1800 you s/b able to put your fingers right on the piping after the OT and it should feel quite cold.
Are your gauges wacked out? Have you used them on another car with working AC?
I know I am grasping at straws but this will end up being something stupid.
I once had a new condenser that had a blockage right at the inlet.
New doesn’t seem to mean anything anymore.
I now use dry shop air to blow thru everything I can before installing.

Having said all that my money is on the OT first
And evap second

Not sure what that meter is testing

[AA/FC]

Yes, the tubing is hot right "before" the O-tube and cold "after" the O-tube. The accumulator also feels cold, like it should.

The gauges COULD be funky, I suppose. The high side pressure gauge on my gauge set matches exactly what the scan tool says for high side pressure so that one is working. Is the low side accurate? Don't know... The low side pressure appears to be where it should be. I've owned these gauges since they were new (probably 20 yeas at this point) and thy have been used on probably 150-200 cars, maybe more. I did replace the hoses and the couplers a few years ago.

The meter is connected to a "K type" thermocouple (temp probe / sensor) and is set on the "temp" setting. It's a multimeter that can also measure temperature. (it's very accurate) I drilled a 1/8" hole in the HVAC box and inserted the thermocouple right in front of the evaporator core. The tip of the temp probe is probably 1/2" from the center/front of the evaporator core. It should be the spot with the coldest air in the entire truck...... and as you can see, it's 50 degrees. The lowest I ever saw was 46, which still isn't nearly cold enough AT the evaporator.

I have put the truck back were it lives when I'm not using it. (for now) When I get time in the next week or two I am going to tear it apart again. I will let you guys know what I find.

Thanks for all the thoughts and suggestions.

[kell490]

I'm assuming it's using an orifice tube is it the right one? When you spray water on the condenser does it blow colder air? You should be getting 40F easily out of that system. I would check the orifice tube I have gotten the wrong one before in a kit from rock auto. I noticed the pressures were not high enough usually on a orifice system the pressure going to go above 200 then cycle where a TXV system will adjust to keep it a constant. Probably some here who do more AC systems then I do but here in Phoenix summer heat a orifice system high side will go up around 225-240 psi low will be in the low 30's maybe even 20's then it will cycle.

There could be a restriction somewhere causing the pressure to look normal but the orifice tube is not getting 200 PSI where it should be getting it. The orifice tube system is like a TXV closed down getting the max pressure until it cycles.

I was thinking maybe the condenser not getting the right airflow for some reason if you spray water from a hose on it get 40F that could be the problem.

[AA/FC]

I'm assuming it's using an orifice tube is it the right one? When you spray water on the condenser does it blow colder air? You should be getting 40F easily out of that system. I would check the orifice tube I have gotten the wrong one before in a kit from rock auto. I noticed the pressures were not high enough usually on a orifice system the pressure going to go above 200 then cycle where a TXV system will adjust to keep it a constant. Probably some here who do more AC systems then I do but here in Phoenix summer heat a orifice system high side will go up around 225-240 psi low will be in the low 30's maybe even 20's then it will cycle.

There could be a restriction somewhere causing the pressure to look normal but the orifice tube is not getting 200 PSI where it should be getting it. The orifice tube system is like a TXV closed down getting the max pressure until it cycles.

I was thinking maybe the condenser not getting the right airflow for some reason if you spray water from a hose on it get 40F that could be the problem.

It's the correct O-tube. It was a genuine GM replacement part. I still have the package. It's the correct tube (part number) for my application. I inspected it before installing it and it looked perfect. No defects that I could see. And it is installed correctly. It is a factory replacement, not one of the VOV auto adjusting, performance O-tubes that you probably see down in the desert. Our summer temps are usually in the mid 80's to 90 degrees with extremely high humidity. The last day I worked on this truck (when the pictures were taken) it was 77 degrees and LOW humidity. There is no way this system will function with any real usefulness when our humidity reaches our summer high points. Remember, humidity adds extra load to the A/C system. It's not like trying to cool a vehicle in dry climates. Although your area gets extremely hot so your A/C systems get a big work out, too...

As mentioned earlier, I am very familiar with spraying water on the condenser trick.... but that is typically when the high side pressure is too high and I suspect there is an airflow problem..... which is NOT the case in this situation. My high side pressure is in the "normal" range for a 77 degree day in the shade. Also, remember, this was a perfectly functioning system before I found the leaky evap core. I never touched the condenser. Well, I did spray the fins out with the water hose but it's wasn't very dirty. It looks brand new still.

I keep hearing about a possible restriction.... But keep in mind, the operating pressure are in the "normal" range. Typically (in my experience, anyway) if there was a restriction that will cause the pressures to be all wacky..... My pressures are not wacky at all. That does not mean there ISN'T a restriction, but chances are that's not the problem.

Like I mentioned above, I will tear it apart in the next week or two and I will let you guys know what I find.

Thank you for your thought and suggestions.

[JohnHere]

The only reason why the evaporator isn't getting sufficiently cold is because not enough liquid refrigerant is making it through the expansion device into the evaporator, where the refrigerant changes state from a liquid to a gas, thus making the evaporator cold, and returning the refrigerant gas (and sometimes, some of the liquid, which is temporarily stored in the accumulator to avoid "slugging" the compressor) to the compressor's suction side.

Therefore, the evaporator probably contains mostly refrigerant gas, which of course won't change state at that point and chill the evaporator as desired.

Why that's occurring, I can only guess at from here. But because the pressures appear to be okay and you've re-charged the system correctly, it seems to me that the problem has to do with either the OT or the evaporator. Hopefully, we'll find out after you tear it back apart.

[JYarber]

Any updates on this? I have a 2006 Sierra 3500 that I just recently redone the entire system and its not cooling that well either. Looking to further diagnosis mine soon.

[JohnHere]

Nothing new that I know of. Suggest starting a separate topic for your vehicle.