I am stumped... 2006 GMC truck

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This problem is with my own truck.... It's a 2006 GMC Sierra 1500 with the 5.3 engine.

I had a leaky evaporator but if I charged the system with refrigerant, it would cool really well. It was a working system that needed a new evaporator.

I decided to replace the evap along with a new Denso compressor, a new accumulator, and a new orifice tube. All the repairs went well. I vacuumed the system for an hour and 15 minutes and achieved a vacuum level of just over 1000 microns. I charged exactly 1.6 pounds of new refrigerant from a brand new 30 pound tank of Chemours Dupont "Freon" r134a. This is an exact charge according to my digital refrigerant scale. I put 2.1 ounces of oil in the new compressor, 1.5 in the new accumulator, and 1.5 in the new evaporator.

Ambient outdoor temp is 77 degrees and my pressures seem normal to me..... at 900 engine rpm, they are right around 35 low / 175-200 high. (depending if electric fans are on or not)

I have a heater core "bypass valve" installed that will isolate the heater core so it gets no hot water from the engine. This SHOULD prevent any cool air loss from having to overcome leaky blend doors in the HVAC box.

I even installed a temp probe in my HVAC box to see the temp of the evaporator. The prob goes into the box roughly 5 inches and the tip of the probe should be right in front of the evaporator on the discharge side. (where the cold air should be)


Why would my vent temps be between 50-60 degrees?

Shouldn't my evaporator be colder than 46-50 degrees?

60 degree vent temps are not acceptable on a 77 degree day, in the shade. lolol.

Any ideas why it's blowing warm?


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A few more pictures....


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[Cusser]

Is your truck regular cab or 4-door truck with dual air? If 4-door, I'd say 1.6 lbs R134a is not enough

[AA/FC]

Is your truck regular cab or 4-door truck with dual air? If 4-door, I'd say 1.6 lbs R134a is not enough

It's a 4 door pickup but it only has front A/C. 1.6 Pounds is the spec for my truck.

[JohnHere]

Try bringing the engine speed up to ~1,800 RPM. At idle speed, the compressor isn't doing much of anything.

[AA/FC]

Try bringing the engine speed up to ~1,800 RPM. At idle speed, the compressor isn't doing much of anything.

Hi

I dove the truck 2.5 hours away from home last weekend (and back) and even at 75mph it still blew 50-60 vent temps.... while outdoor ambient temps never went above 80 degrees the entire weekend.

Is it possible that I received a bad compressor even though the pressures make it look like its working properly?

[tbirdtbird]

This is a long shot but try misting the condenser with water at 1800 and report pressures. Is there any possibility that you have too much oil? Vehicle mileage? Did a comp on the system ever grenade?
Retrace your steps on that.
How many miles on the truck?
OT in backwards?

[AA/FC]

This is a long shot but try misting the condenser with water at 1800 and report pressures. Is there any possibility that you have too much oil? Vehicle mileage? Did a comp on the system ever grenade?
Retrace your steps on that.
How many miles on the truck?
OT in backwards?

I am familiar with the water mist on condenser trick but I didn't try it because the high side pressure is where it needs to be.... plus, when the fans turn on, the high side pressure drops 25-30 psi almost instantly.

160,000 miles on the truck.

It's never grenaded a compressor (I've owned it since new) and that is why I replaced it while I was doing the evaporator. The old compressor seemed fine except for a noisy clutch. I decided to put a new one in BEFORE I had to deal with a grenaded compressor. The original compressor that I just took out is 18 years old. I installed the new compressor for "preventative maintenance".

The new orifice tube is a Genuine GM part. It has an arrow on it just like the original had. I took a picture of the old O-tube while taking it out to make sure I put the new one in the same direction. Between the picture and the arrow, I am 99.99% certain (I am human, after all. lol) the O-tube is in correctly. Plus, I think if the O-tube was in backwards, then I wouldn't be able to get the tubing assembly back together because the O-tube would be sticking out.

To much oil? Possibly. The system holds 8 ounces. The system went dead 2 or 3 times before I found the leak (evaporator core) so it leaked out a bunch of oil through the leaky evap every time it was recharged. Like I mentioned in the original post, I put 2.1 ounces in the new compressor (after I drained the new compressor and refilled with 2.1 ounces from scratch) 1.5 ounces in the new evap, and 1.5 ounces in the new accumulator based on info that I found on the internet. So, with just over 5 ounces of new oil in a system that originally holds 8.... I was thinking it might still be too low on oil. Considering a bunch leaked out when the system went dead the last 2 or 3 times. I don't know.... what's your opinion on that?

I keep retracing everything in my head, over and over.... and I just can't figure this out.

There isn't anything inside the accumulator that could cause this, is there? It's just a desiccant bag in there, right?

I've done plenty of A/C work in the past and this one has me stumped.

[JohnHere]

I decided to replace the evap along with a new Denso compressor, a new accumulator, and a new orifice tube. All the repairs went well. I vacuumed the system for an hour and 15 minutes and achieved a vacuum level of just over 1000 microns. I charged exactly 1.6 pounds of new refrigerant from a brand new 30 pound tank of Chemours Dupont "Freon" r134a. This is an exact charge according to my digital refrigerant scale. I put 2.1 ounces of oil in the new compressor, 1.5 in the new accumulator, and 1.5 in the new evaporator.

I have essentially the same A/C specs for your truck—25.5 ounces net weight of R-134a, and 8.0 fluid ounces of PAG-46—although by my calculations, you might have shortchanged the oil a little.

You added back a total of 5.1 fluid ounces of oil (You did figure "fluid ounces" and not "ounces net weight," correct?). If we figure that the original condenser that you didn't replace retained about 1.5 fluid ounces of oil, that totals about 6.6 fluid ounces currently in the system, leaving a deficit of about 1.4 fluid ounces. That's not to say the oil has anything to do with the elevated evaporator and vent temperatures, though.

Is it possible that the new evaporator came with an OT already installed and then you unknowingly installed another OT?

[AA/FC]

I decided to replace the evap along with a new Denso compressor, a new accumulator, and a new orifice tube. All the repairs went well. I vacuumed the system for an hour and 15 minutes and achieved a vacuum level of just over 1000 microns. I charged exactly 1.6 pounds of new refrigerant from a brand new 30 pound tank of Chemours Dupont "Freon" r134a. This is an exact charge according to my digital refrigerant scale. I put 2.1 ounces of oil in the new compressor, 1.5 in the new accumulator, and 1.5 in the new evaporator.

I have essentially the same A/C specs for your truck—25.5 ounces net weight of R-134a, and 8.0 fluid ounces of PAG-46—although by my calculations, you might have shortchanged the oil a little.

You added back a total of 5.1 fluid ounces of oil (You did figure "fluid ounces" and not "ounces net weight," correct?). If we figure that the original condenser that you didn't replace retained about 1.5 fluid ounces of oil, that totals about 6.6 fluid ounces currently in the system, leaving a deficit of about 1.4 fluid ounces. That's not to say the oil has anything to do with the elevated evaporator and vent temperatures, though.

Is it possible that the new evaporator came with an OT already installed and then you unknowingly installed another OT?

I left the oil a bit shy thinking there would still be some oil in the lines.... Estimating oil can be very tricky.

The evaporator on these trucks do not hold the orifice tube.... The O-Tube is in the high side line under the hood, just before it goes through the firewall and into the evaporator. There is not a spot for a second O-tube to be inserted.

The most confusing part is the normal operating pressures. According to the pressures the system should be working perfectly.

I am going to pull the system apart and double check everything..... but it won't be right away. This is my second vehicle so I don't need it every day. I'm sick of working on it right now but maybe next week I will dig into it again and find the problem. Maybe a defective orifice tube? Maybe a defective evap core? (not sure how that could be defective) Maybe some sort of restriction in the new accumulator? I don't know..... but I will find it.

The original (leaky) system cooled great (when fully charged) until I changed 4 parts..... evap, accumulator, O-tube, and compressor.... one of those new parts has to be defective.