88-94 5.7 Suburban A/C Diagnosis and Tuning

[L31MaxExpress]

Front vents dropped to roughly 30-32°F (measuring driver center vent so I could keep an eye on it) and stayed relatively close on the test drive. I could feel the compressor cycling, but nowhere near as noticable in warmer temperature output as it had been. It is back to cooling the way it should be and did when it was newer on highway trips. It is COLD, finger numbing COLD and it stays cold at all speeds and on both units. I can already tell it will cool well when I take it out tomorrow afternoon, much better than it has been. Also FYI, I think this van just likes the Red Ford 0.062" tube. It has always had great performance with one and noticeably better performance than the White GM 0.072" tube or Ford Blue 0.067". With the Red tube the system pulls down the low side pressure more quickly especially with a heat soaked interior and the air coming out of the vents gets colder sooner. I also believe the Orange 0.057" is just a touch too restrictive which reduces cooling on the highway by causing more frequent compressor cycling.

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[L31MaxExpress]

I think this project is wrapped up for me. I have a couple of things I have to go do later this afternoon and it is forcasted at 108°F later. But I was just out and about in 100°F and 28% RH and I was nice and cool. Not sure which made the bigger impact, my vote is on the expansion valve. The 88947 compressor also surely helped if it is larger displacement than the Sanden which I believe it is. About to put the rear unit all the way back together, put the dash back together and clean the tools I left behind out of the van because it seems good to go. SES light is only on because I have been tuning the VE table and have the MAF disabled.

Practically idling along at 40 mph (engine spinning about 1,200 rpm), got even colder at 70 mph.

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[cjcb1100]

So I have the Old Air expansion valve, 88947 (I went ahead and bought the $50 AC kit to get a lifetime warranty on the compressor) and a Red Ford Orifice tube in my hands. I blew into both the Old Air and wrong chinese valve I returned (Allegidly an OE spec replacement R134a valve with a 2 ton capacity for a 1997 Express with OE rear air). The flow volume on the Old Air valve is easily half. Hopefully that is indicitve that the expansion valve change will fix my unit and I am sure added compressor capacity will not be a bad thing. I mean 10 cylinders instead of 6 should in theory have a bit more capacity. Now I am waiting on my recovery pump and the engine to cool down with a fan on it. First step, get the valve changed and then maybe the compressor will be cool enough to remove.

i have the tbi brakets so thats why i went the sanden sd7h15

 

[cjcb1100]

i think alot of my problem is the slow airflow the early dashes have but atleast its cool enough to make it when its hot will work on it more in the spring just gotta get me through the rest of the summer

 

[L31MaxExpress]

i think alot of my problem is the slow airflow the early dashes have but atleast its cool enough to make it when its hot will work on it more in the spring just gotta get me through the rest of the summer

I felt around under the dash of a friend of mines later dash truck today that has weak vents. He has air leaks in multiple places. Pretty easy problem to correct though. When the foam seals leave the air is free to escape everywhere except the dash vents where you want it. My uncles 94 he had blew like a hurricane even when it was 10 years old with 300K on the clock. I get that it is not fun to pull a dash that might crumble and tear open the heater box. I like using the aluminum duct tape after resealing the ducts with adhesive foam insulation. It helps prevent from having future air leaks.

 

[L31MaxExpress]

i have the tbi brakets so thats why i went the sanden sd7h15

I went with the Sanden too initially. It had a good reputation, however I did not realize it was weaker than the GM HT6 and other options at the time I bought it. The Sanden moves less BTU than the R4 or HT6. That is not as big of an issue in a truck with a smaller cab and front only ac. In my Vortec application, if the 88947 holds up I will be happy with it, I am extremely pleased with how it cools.

 

[L31MaxExpress]

Well I think this newest round of changes has this as good as it will get minus maybe sealing the condenser to the radiator and the radiator to the fan shroud with some adhesive foam weatherstrip.

It warmed up to 109°F and it was ~115°F ambient and a measured 20% RH earlier. I had been on a drive across town and the interior was pre-cooled. The FSM chart stops at 100°F at 20% RH. With R134a GM would not consider the AC broken if it cooled to atleast 54°F at 2,000 rpm while stationary. The Van was rocking 42°F air.

I do plan to have the thing tinted with ATC ceramic heat rejecting limo tint including a shade above my line of vision, no AS1 line on a 97 van and that windshield is tall and very sloped. I also have some door and window weatherstips I need to source and replace, which is not a huge ordeal since GM still builds them. There is some wind noise and air leakage in the 26 year old weatherstripping. I am also thinking of dynamating the engine cover exterior. A lot of heat and noise finds its way through the OE insualtion. The OE insulation is basically like the heat insulation on a hood that has been covered in heavy baking aluminum foil, thin, crumbling and basically useless.

That being said AC system wise, I do not see being able to get anything more from it, save adding some tacky tape to the case around the evaporator core lines that are still leaking air under the hood even after I replaced the OE foam weatherstrip and taping up some leaking joints under the dash. There is a substantial volume of cold air still blowing out under the hood and behind the dash. It is still blowing great, but I want all the airflow in my face lol. The blower motors do run a bit slower now with the PCM regulated alternators 12.8-12.9 volts output. I really need to upgrade the wiring from the alternator to the battery and the battery to the fuse block and perhaps add the remote sense wire from the alternator to the fuse block that the 8.1L vans used. I think that remote sense wire might kick up the system voltage when there is a heavy electrical demand. Never understood why the 8.1Ls got that wire but the normal 4.3L, SBC and LS powered vans did not. All 01+ were PCM controlled but only the 8.1Ls got that additional circuit and voltage referenced feature.

I can get the ac cold, now I just need to keep the heat out.

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[cjcb1100]

my blower sucks they all do does the van have the same blower motor?

 

[L31MaxExpress]

my blower sucks they all do does the van have the same blower motor?

They do not and my 99 Tahoe has a revised blower as well. The Genuine GM blowers are better than the cheap parts store garbage in regards to airflow as well. The squirel cage is more open and they have longer vanes that grab more air. The GM blower also has a ring that goes deeper into the air inlet that helps prevent airflow from bypassing back into the squirel cage. I discovered this a while back, changed the blower motor out and had 2x the airflow.

I retrofitted an Express blower and resistor to my 1983 G20 van and will be adding the same to the 87 van. I am also upsizing the power and ground wires on the 87s blower for the High blower function. It is like 12 or 14ga from GM and it will get 10ga. It will also no longer receive power from the overloaded bus terminal that likes to overload, melt and catch fire on these vans. I have seen more than one melt parts of the harness and start to catch fire because of the shoddy GM engineering on that connection. The C10s have almost the same connection and problem as well.

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[cjcb1100]

as far as i researched the trucks dont have anything as far as upgrades or mods kinda stuck with what we can get