88-94 5.7 Suburban A/C Diagnosis and Tuning

[L31MaxExpress]

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

It is just a slight mounting and wiring difference between the later model Tahoe or Express blower. The squirel cage size and foot print is basically the same.

 

[L31MaxExpress]

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[L31MaxExpress]

On the G20 van I had to trim down the flanges a bit, drill a couple new holes in the flange, pirate a connector from a van I parted out. But it went right in place of the blower on my 1983 G20 that was the same blower you have. A sharp pair of tin snips cut right through the metal flange. I made a template from poster board and cut it down to match the templete. I sealed it to the firewall with dum dum or butyl/tacky tape, whatever your prefered name for it is. The vents blew twice as hard, not even joking. Drastic improvement. The OE wiring on the Express is the same size too but they have a better resistor design. Most of the magic in the Express blower is the squirel cage. Could probably snag one from the wrecking yard, remove both and swap the wheel to your trucks blower.

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[L31MaxExpress]

Actually looking at the pictures on Rockauto the GM genuine blower has been re-designed with the newer style wheel anyway. If yours has the fat plastic, short vane, closed off wheel, this would be a big improvement in itself.

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[cjcb1100]

nice may get one soon mine is tired

 

[Wildblue19]

Great work on your system @L31MaxExpress ! I have been traveling for work last 10 days so unable to get data on my system. That will hopefully change this coming weekend.

Do you recall if the old air valve is metric or sae threaded? I may try that out. After swapping my rear valve pressures are only up on the low side for me. Rock auto lists the orifice as larger for the 134 valve as expected but i think i may be flowing too much now. I have yet to get hands on it to check superheat and subcool but it is not likely severely under or overcharged. Yet, idle vent temps are 70° in 106° ambient. Not good enough.

I agree a dual air truck should get as big a pump as possible. But thats why i got the biggest sanden I could find, at least on paper it would be on par with your four seasons or better....

Interestingly, the rear air on mine was now consistently 7-10° cooler than the front after the change. It was always a little better, but significantly so now.

 

[L31MaxExpress]

Great work on your system @L31MaxExpress ! I have been traveling for work last 10 days so unable to get data on my system. That will hopefully change this coming weekend.

Do you recall if the old air valve is metric or sae threaded? I may try that out. After swapping my rear valve pressures are only up on the low side for me. Rock auto lists the orifice as larger for the 134 valve as expected but i think i may be flowing too much now. I have yet to get hands on it to check superheat and subcool but it is not likely severely under or overcharged. Yet, idle vent temps are 70° in 106° ambient. Not good enough.

I agree a dual air truck should get as big a pump as possible. But thats why i got the biggest sanden I could find, at least on paper it would be on par with your four seasons or better....

Interestingly, the rear air on mine was now consistently 7-10° cooler than the front after the change. It was always a little better, but significantly so now.

The old air valve is SAE, a #6 feed line and #8 to the evaporator. That is why the first valve I purchased was wrong and I initially cross referenced the valve to the Four Seasons 38693.

It has cooled off dramatically here this evening, but the forcast shows it to be short lived.

I sealed up the air leaks in the front case under the hood with dum dum tape.

I also put foam insulation next to the condenser and between the radiator and fan shroud. I used the 1" square stuff you insulate window units with. I ended up discovering dum dum sticks to everything. I stuck them in place with some dum dum. I need to see if I can find some 2" square foam for the condenser side, the 1" stuff left a small gap, but better than nothing. I could have also filled that gap with some aluminum duct tape, but I did not have any at the shop


I drove it 100 miles tonight. It was not far down the road before I had shut the rear unit off, the front unit was on the lowest fan speed, and I had to knock the recirculate off. I stopped at a traffic light half way into the trip, turned on the dome light and the dash vents at that point were at 26°F. The setting I had previously adjusted the cycling switch to must work well. The evaporator never froze solid or enough to even notice a loss of airflow despite the massive humidity. The compressor was cycling approximately every minute. These large systems act like large accumulators. The compressor stays off as long as it stays on. I had a 2nd thermometer laying on top of my center console. It was reading 60°F.

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[L31MaxExpress]

Update on my repairs. While it is no longer 108°F, I have seen the AC temps drop down as low as 26°F out of the front vents driving around. The 2nd fan speed notch on the front unit is generally enough to stay plenty cool out on the highway. I use low fan speed on the rear unit and then turn it off after the interior cools down. While I had the engine cover off, I re-insulated it. Wish I could have purchased a new weatherstrip but it is long discontinued, may order one for a newer van at some point and cut it down to fit.

The GM weatherstrips for the front doors I ordered a while back finally arrived and took all of 10 minutes to install. The 27 year old OE GM ones were compressed flat and splitting in half. Doors shut solidly now and hopefully a bit less wind noise. Overall I am staying cool and that makes me happy.

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I may get more of the same material I insulated the engine cover with, pull the front seats out, lift up the carpet, and insulate both the firewall and front floor area a distance equal to the underfloor catalytic converter heat shields as another van guy on one of my groups has. What I used is an adhesive backed closed cell foam with an aluminum layer on the face. I held a torch to the foam side of a small sample piece and it will not burn. It adds an insulation value of around R13 to what is already there with the heatshield, floor, carpet padding and carpet. It is a dense, heavy material similar to Dynamat.

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[Wildblue19]

Nice work @L31MaxExpress. I redid all my weather stripping about 2 years ago and it made a big difference. When I was at SEMA last year, I talked with a sound deadening company, the name escapes me for now. They confirmed that for the automotive use case, the best thing you can do with regards to heat, vibration, and road noise is a combination of products. A quick recap;

Stick on kilmat or any other heavy tar mat alternative should be your base layer, which adds mass to the large flat panels to kill reverberation. When I laid mine down, I did it similar how you did and tried to get 100% coverage. This isn't required, since it adds minimal insulating value and the primary purpose is vibration damping. There are several interesting videos on the subject, and most suppliers recommend it only in 60-80% panel coverage, on the large, flat areas. Panel vibrations are complex, with lots of localized nodes - the heavy kilmat disrupts the nodes across the panel without needing to cover it entirely.

For heat, a closed cell foam should go on top of the kilmat, thicker is better and open cell should be avoided due to water absorption issues. Neither of these options will really kill road / wind noise that isn't caused by panel reverberation.

For noise damping, you really want a mass-loaded vinyl (MLV) of a minimum of 1lb/sqft, but 2lb/sqft is preferred. Mass that is decoupled from the vehicle body is what kills noise. The guys I was talking to at the show had a MLV-closed cell foam composite that looked promising. It is really important that the MLV is decoupled from the body, IE not connected via any adhesives - if it is attached in this manner, the noise will simply transmit through the material instead of being stopped by it.

So, the best stackup would be kilmat, closed cell foam, as thick as you can afford, and a MLV laid on top without an adhesive. The real downside is 1, cost, and 2, thickness of the material stackup, that can really make re-fitting the carpets and wires a pain. Plus, a 2lb/sqft MLV will add a couple hundred pounds to our already heavy vehicles. But, this is how serious car audio guys and the luxury cars get extremely quiet, insulated interiors.

 

[L31MaxExpress]

Nice work @L31MaxExpress. I redid all my weather stripping about 2 years ago and it made a big difference. When I was at SEMA last year, I talked with a sound deadening company, the name escapes me for now. They confirmed that for the automotive use case, the best thing you can do with regards to heat, vibration, and road noise is a combination of products. A quick recap;

Stick on kilmat or any other heavy tar mat alternative should be your base layer, which adds mass to the large flat panels to kill reverberation. When I laid mine down, I did it similar how you did and tried to get 100% coverage. This isn't required, since it adds minimal insulating value and the primary purpose is vibration damping. There are several interesting videos on the subject, and most suppliers recommend it only in 60-80% panel coverage, on the large, flat areas. Panel vibrations are complex, with lots of localized nodes - the heavy kilmat disrupts the nodes across the panel without needing to cover it entirely.

For heat, a closed cell foam should go on top of the kilmat, thicker is better and open cell should be avoided due to water absorption issues. Neither of these options will really kill road / wind noise that isn't caused by panel reverberation.

For noise damping, you really want a mass-loaded vinyl (MLV) of a minimum of 1lb/sqft, but 2lb/sqft is preferred. Mass that is decoupled from the vehicle body is what kills noise. The guys I was talking to at the show had a MLV-closed cell foam composite that looked promising. It is really important that the MLV is decoupled from the body, IE not connected via any adhesives - if it is attached in this manner, the noise will simply transmit through the material instead of being stopped by it.

So, the best stackup would be kilmat, closed cell foam, as thick as you can afford, and a MLV laid on top without an adhesive. The real downside is 1, cost, and 2, thickness of the material stackup, that can really make re-fitting the carpets and wires a pain. Plus, a 2lb/sqft MLV will add a couple hundred pounds to our already heavy vehicles. But, this is how serious car audio guys and the luxury cars get extremely quiet, insulated interiors.

To be fair, the thick sound deadener jute material and thick carpet the conversion company installed keeps a lot of the road noise down, compared to the base cargo and passenger vans. The interior of this van was probably a solid 5-7 decibels quiet that the same van as built by GM. I am probably just being picky. The weatherstriping I really need to find is what they use to seal the aftermarket sliding windows. Those windows are built like the sliding windows in campers and RVs, so probsbly not overly difficult to source. Those small windows occasionally whistle.