High AC pressure

[Mr.Tarver]

I apologize ahead of time because this will be a little long, but I want to try to tell the whole story. I am having some odd AC issues lately. I need to give a little back story and information first. My truck is a 1984 K5 blazer I purchased last fall. When I got it, it had very tired 350/350 combo, and I purchased it with the intent on swapping in an lq4/4l80e that I already had. Before I got it someone had recently done some AC work. It had a sanden 508 swapped on it, a new evaporator, new dryer, and a new parallel flow condenser. I never really was able to use the AC since I bought it later in the year and the weather was cool. Well fast forward to my LS swap, I ended up needing to put another compressor on it because the one that was on it was a V belt and I needed a serpentine setup. I looked at buying a new pulley/clutch for it but it was the same price more or less to buy another compressor, so that's what I did. Now I have the truck running, but it runs very poor, it's extremely rich and will fuel smoke bad for a bit. It's not completely stock and it doesn't have O2 sensors on it yet, it needs a tune. However, before I can get the truck tuned, I needed new exhaust ran. So, while I'm waiting on my appointment for the exhaust shop to get here, I'm buttoning up loose ends and trying to make use of the down time. So, I decided to charge the AC system. I'm able to pump the system down good and get it to hold a good vacuum, so I begin to charge the system. I get one can into it and the compressor is starting to kick on and off. I begin to put a second can in and my low side pressure starts to rise pretty high. I shut the valve on the gauge and just watch it. The pressure with the compressor running is 100 on the low side, and about that on the high side. So, I stop, I purge the system until the pressure looks normal and the compressor stops running constantly. Everything looks good, so I begin to put the second can in and everything looks great. I finish with a third can and I'm able to get the pressure to about 35 on the low and 200 on the high side. The next day I go to move the blazer out of my garage, again it runs very poorly and the transmission is defaulted to starting in 2nd gear due to the lack of a segment swap in the ecu. So, it's kind of a task just to get it to move under its own power without dying, I eventually get it out to the yard and just let it sit and idle for minute. Then there's a huge pop and I can see vapor everywhere under the hood. I go look and see that it's blown a high side line apart. The only thing I can figure is that there must be some sort of a restriction in the system to make the pressure get high enough to do that. So I pulled the orifice tube and found a small bit of metal and a little grit, but honestly nothing too concerning to me. I order a new orifice tube and dryer. Finally last night I get everything on and get the system pumped down and ready to charge again. I begin to charge the system and I get the exact same thing happening as last time, low side pressure is over 100 and the high side is bouncing between 350 and 400! Again, I stop and purge the system, pressures drop to normal and I finish charging. Low side is 45, high side is 250. Vent temps are cold and it appears to be working fine. So now I'm very puzzled as to what caused those crazy pressures. What makes the whole thing very odd to me is that when the pressures were crazy high the engine was running awful, the idle was surging bad. Then when everything evened out it idled pretty smooth. So, I'm trying to determine which is the cause/effect. Was the idle changed because the load dropped with the lower pressure? Was it a coincidence? Because the idle changing also happened to be the same time the fans kicked on and everything was at operating temp. It's just strange to me that everything seemed to fall into place at the same time like that. Is it possible there's a restriction in the system? If so, then why would the pressures return to normal? Could it be an issue with the compressor itself? Any help is greatly appreciated.

[Shifty One]

If there is metal in the orifice, there will be in the condenser as well. The tubes are itty-bitty on them compared to the gool old r12. There may be other things going on, but that is a most likely thing....and no amount of flushing will get it all out either.

[Rich84]

First i am no expert..Having said that, I remember how my LQ4 ran without O2 sensors. I don't think that is the best way to get an ac system's initial charge. It ran like Poo and the ac does put a load on it.

[Jeepwm69]

Originally Posted by Mr.Tarver

I apologize ahead of time because this will be a little long, but I want to try to tell the whole story. I am having some odd AC issues lately. I need to give a little back story and information first. My truck is a 1984 K5 blazer I purchased last fall. When I got it, it had very tired 350/350 combo, and I purchased it with the intent on swapping in an lq4/4l80e that I already had. Before I got it someone had recently done some AC work. It had a sanden 508 swapped on it, a new evaporator, new dryer, and a new parallel flow condenser. I never really was able to use the AC since I bought it later in the year and the weather was cool. Well fast forward to my LS swap, I ended up needing to put another compressor on it because the one that was on it was a V belt and I needed a serpentine setup. I looked at buying a new pulley/clutch for it but it was the same price more or less to buy another compressor, so that's what I did. Now I have the truck running, but it runs very poor, it's extremely rich and will fuel smoke bad for a bit. It's not completely stock and it doesn't have O2 sensors on it yet, it needs a tune. However, before I can get the truck tuned, I needed new exhaust ran. So, while I'm waiting on my appointment for the exhaust shop to get here, I'm buttoning up loose ends and trying to make use of the down time. So, I decided to charge the AC system. I'm able to pump the system down good and get it to hold a good vacuum, so I begin to charge the system. I get one can into it and the compressor is starting to kick on and off. I begin to put a second can in and my low side pressure starts to rise pretty high. I shut the valve on the gauge and just watch it. The pressure with the compressor running is 100 on the low side, and about that on the high side. So, I stop, I purge the system until the pressure looks normal and the compressor stops running constantly. Everything looks good, so I begin to put the second can in and everything looks great. I finish with a third can and I'm able to get the pressure to about 35 on the low and 200 on the high side. The next day I go to move the blazer out of my garage, again it runs very poorly and the transmission is defaulted to starting in 2nd gear due to the lack of a segment swap in the ecu. So, it's kind of a task just to get it to move under its own power without dying, I eventually get it out to the yard and just let it sit and idle for minute. Then there's a huge pop and I can see vapor everywhere under the hood. I go look and see that it's blown a high side line apart. The only thing I can figure is that there must be some sort of a restriction in the system to make the pressure get high enough to do that. So I pulled the orifice tube and found a small bit of metal and a little grit, but honestly nothing too concerning to me. I order a new orifice tube and dryer. Finally last night I get everything on and get the system pumped down and ready to charge again. I begin to charge the system and I get the exact same thing happening as last time, low side pressure is over 100 and the high side is bouncing between 350 and 400! Again, I stop and purge the system, pressures drop to normal and I finish charging. Low side is 45, high side is 250. Vent temps are cold and it appears to be working fine. So now I'm very puzzled as to what caused those crazy pressures. What makes the whole thing very odd to me is that when the pressures were crazy high the engine was running awful, the idle was surging bad. Then when everything evened out it idled pretty smooth. So, I'm trying to determine which is the cause/effect. Was the idle changed because the load dropped with the lower pressure? Was it a coincidence? Because the idle changing also happened to be the same time the fans kicked on and everything was at operating temp. It's just strange to me that everything seemed to fall into place at the same time like that. Is it possible there's a restriction in the system? If so, then why would the pressures return to normal? Could it be an issue with the compressor itself? Any help is greatly appreciated.

I ran into a similar situation not too long ago on my 1994 Honda Accord. I had to replace the evaporator core (leak) and put it all together, vacuumed it down, and added 2 cans of freon. What I neglected to do is plug the fan timer (kicks fans off with car shut off to cool down system) back in, so the fans didn't kick on at all with that timer unplugged.

What I think happened is, without fans pulling air across the condenser, the coolant wasn't being sufficiently cooled, which made the compressor really struggle to flip on and off. When the compressor would kick on, it would almost stall the engine. High side pressure was WAY up, and while it was blowing cold air, I could tell something wasn't right. I drained system, removed evap core to make sure I didn't have a blockage there in the new evap core. It was fine, so reinstalled, vacuumed, and THIS time I remembered to plug in the fan timer. Charged it up and it's been working great for a couple of months.

Hard wire your fans on and see if the thing works like it should. Given that you have a cobbled together system that was not as it was originally designed, that would be my guess at your problem.

I'd love to see pics of the Sanden on an 84 350. I have an 83 GMC with 305 and would like to swap a Sanden in, but the brackets etc that I see are all for serp setups, not v belts. I bought a Dirty Dingo bracket set and compressor to swap a Sanden onto Dad's 95 GMC, replacing the R4. Would really like to do the same on my 83, and would like to see your setup for reference.

[Shifty One]

FWIW, Alan Grove makes your v-belt brackets....Mine is up and running fine with the Sanden.