88-94 5.7 Suburban A/C Diagnosis and Tuning

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
5,892
Reaction score
7,543
Location
DFW, TX
Sorry if this is the wrong place/time to ask this question, but - do you guys think that those pusher fans hurt the engine cooling while driving at speed?

Thanks.
I think that one GM designed fan will not hurt a thing. My Tahoe has always run cool going doen the road. Since it was factory, the PCM controls it. I think it shuts off at 40 or 50 mph.
 

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
5,892
Reaction score
7,543
Location
DFW, TX
Weather has changed here a bit and it was threatening to rain and actually is now.

It was 89°F and 70% humidity so my pressures and temps are not what they were when it was hot and dry, but the system is under a very heavy cooling load.

I only tested idle at 750 rpm and as high as the engine would rev with the IAC wide open. Ended up being 1,150 rpm. I brought the engine up to 2,100 but it started cycling the compressor and the pressure readings were not consistent.

Has not run in a few days. I had yet to tie into the high side line. Temps are both showing 88.8
You must be registered for see images attach


Short time into the test.
You must be registered for see images attach


I had the high side temp probe on the compressor outlet an the low side on on the evaporator suction port ahead of the accumulator
xc_hide_links_from_guests_guests_error_hide_media

Engine had been running 15-20 minutes at this point.
You must be registered for see images attach

I then moved the high side probe to just ahead of the orifice tube, and waited for it to stabilize.
You must be registered for see images attach


At this point the inside of the van was an igloo inside and I had 2 decent sized puddles of water forming on the shop floor.
 
Last edited:

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
5,892
Reaction score
7,543
Location
DFW, TX
At that point I fired up HP Tuners and commanded 1,500 rpm. The IAC fully opened and the engine reved up to ~1,150 rpm. I waited about 10 minutes for the system to stabilize.
You must be registered for see images attach


You must be registered for see images attach


You must be registered for see images attach


xc_hide_links_from_guests_guests_error_hide_media

I finally moved the high side probe back to the compressor once again.
You must be registered for see images attach


I moved the cold side probe 4 times during each test and the values stayed within 1-2°F. I checked the evaporator inlet after the orifice, the suction outlet at both the evaporator and accumulator. The compressor manifold inlet was 4-5°F warmer.
 
Last edited:

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
5,892
Reaction score
7,543
Location
DFW, TX
Also feel this is worth mentioning, the rattle like sound is not the compressor, its nearly dead silent. Its the roller valvetrain in the 383.
 

Wildblue19

I'm Awesome
Joined
Jul 21, 2020
Messages
289
Reaction score
703
Location
Lone Star
Thanks for the really good info @L31MaxExpress. I haven't been able to touch the truck since Monday with work being busy but intend to compare results when I can.

I'm looking at methods of wiring in the pusher fan for the condenser. GM ran it off a relay from the compressor clutch for the 800's as you said in their service bulletin, however a fair number of third parties like Vintage air advocate for a trinary switch. I can evacuate the system and crimp in a fitting to mount a trinary, is it worth the trouble of plumbing in? I haven't found much documentation on doing that in a GMT400 in a brief search.
 

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
5,892
Reaction score
7,543
Location
DFW, TX
Thanks for the really good info @L31MaxExpress. I haven't been able to touch the truck since Monday with work being busy but intend to compare results when I can.

I'm looking at methods of wiring in the pusher fan for the condenser. GM ran it off a relay from the compressor clutch for the 800's as you said in their service bulletin, however a fair number of third parties like Vintage air advocate for a trinary switch. I can evacuate the system and crimp in a fitting to mount a trinary, is it worth the trouble of plumbing in? I haven't found much documentation on doing that in a GMT400 in a brief search.

I would just wire it to the clutch myself and be done with it. You could add a trinary but the single pusher fan is not going to really benifit too much from one. The pressures should stay lower if the fan runs when the ac is on, rather than waiting until pressure builds to enable. On LS setups I tune with electric fans, I bring low speed fans on with clutch engagement or around 140 psi if they have a sensor. That is far earlier than GM turns them on, but its better to get some airflow going across the condenser.

I had the relay on my auxiliary fan on my G20 van wired to the high blower relay turn on from the dash switch forever and a day on it. My normal move on a hot interior was to move the switch to high fan speed. Once I got rolling down the highway and the interior had cooled down, dropping the fan speed down a notch disabled the pusher fan. With less airflow across the evaporator and a cooler interior the pressures stayed low enough that the auxiliary fan was not needed anyway. Stuck in a traffic jam as the interior started warming up, flip the blower to high and the auxiliary fan came on. The relay kit I put on also had a temp switch I put into the passenger side head. Turned the pusher fan on at 195°F for added cooling. I had a 180°F thermostat. When I shut the van off heat soaked that 12" pusher would run for a while to cool the engine and engine compartment down. Really helped the hot restart when it was carbureted.
 
Last edited:

Wildblue19

I'm Awesome
Joined
Jul 21, 2020
Messages
289
Reaction score
703
Location
Lone Star
I've got the e fan parts in the mail.

Side note, if anyone happens to have an anemometer or knows what the approximate vent air speed should be drop a reply.

In my 93, on high, recirc off, the average across all front vents was right around 10mph with the vehicle static. Measured with the fan parallel to the vent face and flush against it Recirc on, it was about 11mph. Rear fan blew harder on high with the middle row vents averaging about 15mph.

You must be registered for see images attach
 

Wildblue19

I'm Awesome
Joined
Jul 21, 2020
Messages
289
Reaction score
703
Location
Lone Star
Decided to answer my own question, went and installed a new 4seasons blower the local store had for about 40 bucks. Gained me about 1.5mph vent speed up front, not much to write home about but still over 10% increase.

Condenser was clean, no debris. Recirc seals are still soft, but are permanently deformed from sitting I suppose. Leaves about a 1/4" air gap around one edge which explains the poor cooling difference between fresh air and recirc selected.
 

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
5,892
Reaction score
7,543
Location
DFW, TX
I've got the e fan parts in the mail.

Side note, if anyone happens to have an anemometer or knows what the approximate vent air speed should be drop a reply.

In my 93, on high, recirc off, the average across all front vents was right around 10mph with the vehicle static. Measured with the fan parallel to the vent face and flush against it Recirc on, it was about 11mph. Rear fan blew harder on high with the middle row vents averaging about 15mph.

You must be registered for see images attach
Decided to answer my own question, went and installed a new 4seasons blower the local store had for about 40 bucks. Gained me about 1.5mph vent speed up front, not much to write home about but still over 10% increase.

Condenser was clean, no debris. Recirc seals are still soft, but are permanently deformed from sitting I suppose. Leaves about a 1/4" air gap around one edge which explains the poor cooling difference between fresh air and recirc selected.

I resealed my evaporator case and put a new GM blower motor on mine. It literally feels like it blows 2x as hard. Mine had a substantial air leak underhood. I do not have an Anemometer but it would be skewed. I have 7 dash ac vents in the van and the Tahoe has 6 dash vents. 95+ got the ball chiller vents as well as larger dash vents. I think they have a more powerful blower as well.

My rear ac needs a new blower motor as the bushings are starting to make noise. I have a Spal replacement on the way for the aftermarket rear unit. I need to change the rear heater hoses and the rear expansion valve. Hoses are original to the van and I have HPS silicone bulk hose to replace them with. The rear expansion valve keeps sticking closed at times.
 
Top