Complete new A/C system problem? Help!!

V

Vettepilot

Joined
Mar 10, 2022
Messages
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Restoring a 1994 GMC K1500 with 5.7 V/8. I installed virtually ALL new A/C system components, except the evaporator. I thoroughly flushed the evaporator, and pressure tested it for leaks. (None)

Vacuumed the system down for one hour plus, and then the system held the vacuum overnight with vacuum pump disconnected. I then started to charge the system as normal. Often times, if I work quickly, I can get enough freon into the system just from the vacuum, that the compressor will kick in and I don't need to bypass the pressure switch. In this case however, there was an electrical problem and the compressor didn't turn on. The system took a little under two cans on it's own, (about 20 ounces +/-) without the compressor running. Capacity is 32 oz.

When I finished fussing with the electrical problem and got back to tending the gauges, things were all out of whack. The low side is pegged high, and when the compressor is on, the high side quickly (in about ~5 seconds) goes to emergency cut off at 450 psi plus, then the safety switch kicks in and turns the compressor off. Static, engine off pressures are Low side = pegged, High side = 125 psi.

What's wrong here, and what's the fix???

Thanks!
Vettepilot
 
Shouldn't the high and low side pressures eventually equalize with the system and engine off?

Any chance the orifice tube was installed backwards (I don't think this matters but.....)?
 
Not overcharged, as system calls for 32 oz and I only put in 20 oz. But yeah, it kinda acts like a severe overcharge, or a blockage. Virtually all new parts except evaporator. I know that isn't clogged because I cleaned/flushed it. Orifice tube only fits one way.

System calls for 8 oz. total oil. New compressor came with a decal saying it had 7 ounces, so I added one ounce to the accumulator.

I'm stumped, and really bummed. I spared no expense to have this system perfect, and here I am....

I was hoping the system would normalize/equalize overnight, but no change. Pegged at well over 120+ on low side, 150 psi on high side while static/not running. It's a really good thing this system has the emergency cutout sensor on the compressor, because the pressure builds instantly to 450 psi+ and climbing fast. Something would have blown if it hadn't automatically shut the compressor down.

Thanks,
Vettepilot
 
Well, guess what. Even though I tried to buy quality parts, they're all made in China anyway, and the A/C lines at the condensor were a really, really poor alignment/fit. You know where this is going, huh? Yep, I accidentally swapped the lines at the condensor, right where the Orifice tube is located...

Embarrassing.

So, lines are swapped back and vacuuming back down for an hour or so again right now.

THANKS!
Vettepilot
 
Vettepilot said:
Well, guess what. Even though I tried to buy quality parts, they're all made in China anyway, and the A/C lines at the condensor were a really, really poor alignment/fit. You know where this is going, huh? Yep, I accidentally swapped the lines at the condensor, right where the Orifice tube is located...

Embarrassing.

So, lines are swapped back and vacuuming back down for an hour or so again right now.

THANKS!
Vettepilot
Click to expand...
Just curious if this discovery resulted in a fully functional system. Hoping so, as hot as it's been around the country!
 
I had it all vacuumed down and was about to charge it when my well used hose and gauge set finally gave up last evening. and we also discovered an HVAC actuator inop in the cab. Ordered a new gauge set and a gear for the actuator.

Thanks for asking.

Vettepilot
 
Vettepilot said:
Well, guess what. Even though I tried to buy quality parts, they're all made in China anyway, and the A/C lines at the condensor were a really, really poor alignment/fit. You know where this is going, huh? Yep, I accidentally swapped the lines at the condensor, right where the Orifice tube is located...

Embarrassing.

So, lines are swapped back and vacuuming back down for an hour or so again right now.

THANKS!
Vettepilot
Click to expand...
Fairly easy mistake to make since they used the same size connectors on these for whatever reason and they are right next to each other. I've rebuilt a few of these AC systems over the years and all it takes is one little mistake like this to cause a huge issue. And yes, the fact that almost everything you buy now is made in China really doesn't help. Got a condenser once for my brother's 97 Chevy K1500 and it had the threads cut wrong for both connections. Took me a while to figure out why I couldn't get the line nuts started on them until I gave them a closer look and saw they were a different size thread. Back to the store it went for an exchange for one that I checked before leaving with the part.
 
Maybe you guys can still help. My owners manual for this truck says 36 oz. of R-134. One video I happened to be watching stated 36 oz. as well.

However, my Four Seasons capacity guide, and another source say 32 oz.

Unfortunately I don't have the factory service manual, and there's no decal on the truck.

How much would you put in??

1994 GMC K1500 extended cab Z-71 4x4

Thanks,
Vettepilot
 
Vettepilot said:
Maybe you guys can still help. My owners manual for this truck says 36 oz. of R-134. One video I happened to be watching stated 36 oz. as well.

However, my Four Seasons capacity guide, and another source say 32 oz.

Unfortunately I don't have the factory service manual, and there's no decal on the truck.

How much would you put in??

1994 GMC K1500 extended cab Z-71 4x4

Thanks,
Vettepilot
Click to expand...
If it's a 2 door 32 oz. A 4 door takes 36 oz. Do you have air flow across the condenser? Will you post a pic of the new vs old condenser for me?
 
It is 36 oz. for the extended crew cab and 32 oz. for the standard cab per the Four Seasons guide:

1691192299867.jpg
 
The problem was the lines reversed at condensor. Old condensor disposed of and grill is re-installed, so sorry, no pics.

One note though. Many condensors have "O" tube in bottom line, but these have them in the top.

Vettepilot
 
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