Better AC with different size pulley?

JohnZ71 · Jun 22, 2024

With the recent heat wave, the AC once again leaves a lot to desired once idling in the torturous midday sun.

Had my AC guy check the refrigerant, pressures, airflow, etc. All was good. The AC is great if it’s below 90 outside. Once it gets over 90 it starts struggling at idle.

I can elevate the rpm’s slightly and can immediately tell a difference. More air is pulling through the condenser, but also the compressor is spinning faster obviously. Which of the two makes the bigger difference?

It crossed my mind that I could install a smaller pulley on the AC compressor to make it spin a little faster at idle, has anyone done this with noticeable results?

Also all I’ve seen is underdrive crank pulleys. Do they make an overdrive one?

Just some ideas I’m tossing around. Maybe the heat is taking it’s toll on me.

I should also mention that I use a severe duty clutch with the 9(?) blade plastic fan, it engages constantly and stays locked in. Also have the factory auxiliary electric fan, it stays on with a manual switch.

Vikingdude · Jun 22, 2024

Some folks will wire in a relay to control an electric fan on the condenser. I think a few companies make a kit.

CumminsFever · Jun 22, 2024

My dad had a shop for 25 years. In years of working on the gmt400 platform, the a/c was a constant source of complaints. His "fix" was a severe duty fan clutch, variable orifice tube, and the suburban dual-air compressor clutch (or whole compressor if it needed one). That would be the smaller diameter pulley. This was as good as it got for stock parts.
A local radiator shop took that recipe a step farther and would install a universal high-efficency condenser.
I've not yet heard of a larger crankshaft pulley.
I most cases, we saw the most difference from the variable orifice tube.

95 Tahoe · Jun 22, 2024

I have a 95 Tahoe with mostly a stock AC system. I am using the Ford Red Orifice tube and an adjustable pressure switch. It takes a while for the large area to cool down. At idle in 95 degree heat it still climbs to the mid 50's. Driving it's about 42F. Also, the 11 blade fan helps GM 1580739. It was a direct drop in on my 95. I also have the electric condenser fan. It came on the Suburban's of the same year model. I do not think these will ever cool like a new truck.

L31MaxExpress · Jun 22, 2024

95 Tahoe said:
I have a 95 Tahoe with mostly a stock AC system. I am using the Ford Red Orifice tube and an adjustable pressure switch. It takes a while for the large area to cool down. At idle in 95 degree heat it still climbs to the mid 50's. Driving it's about 42F. Also, the 11 blade fan helps GM 1580739. It was a direct drop in on my 95. I also have the electric condenser fan. It came on the Suburban's of the same year model. I do not think these will ever cool like a new truck.

Both of mine cool better than most newer vehicles. I have seen mid 20s vent temps in the 97 van and 99 Tahoe before the compressor cycles in Texas heat. My 87 G20 will also get low 30s before the compressor cycles. The limitation I have found is the evaporator core freezing. I can easily turn them into a solid block of ice.

L31MaxExpress · Jun 22, 2024

JohnZ71 said:
With the recent heat wave, the AC once again leaves a lot to desired once idling in the torturous midday sun.

Had my AC guy check the refrigerant, pressures, airflow, etc. All was good. The AC is great if it’s below 90 outside. Once it gets over 90 it starts struggling at idle.

I can elevate the rpm’s slightly and can immediately tell a difference. More air is pulling through the condenser, but also the compressor is spinning faster obviously. Which of the two makes the bigger difference?

It crossed my mind that I could install a smaller pulley on the AC compressor to make it spin a little faster at idle, has anyone done this with noticeable results?

Also all I’ve seen is underdrive crank pulleys. Do they make an overdrive one?

Just some ideas I’m tossing around. Maybe the heat is taking it’s toll on me.

I should also mention that I use a severe duty clutch with the 9(?) blade plastic fan, it engages constantly and stays locked in. Also have the factory auxiliary electric fan, it stays on with a manual switch.

The compressor spinning slow is the bigger issue. Stay away from the Sanden replacement, even with the small pulley it is woefully inadequate at lower rpm. For a 96+ Vortec, the Four Seasons 10 cylinder HT6 upgrade moves a lot more refrigerant. Get one for an Express van as it has the smaller pulley on it. On the trucks, I use the larger Suburban/Tahoe dual air condenser. Have to move the mounts and get new GM cushions to fit the upgraded microtube parallel flow style condenser. On the Vortec era trucks the holes are typically already in the core support for the wider condenser. The difference is a ~27" wide condenser core vs ~34" wide core. The condenser cost about the same $ so it is a nearly free upgrade when the system is being renewed anyway. You cannot flush the condensers on these trucks as they have multiple flow paths.

L31MaxExpress · Jun 22, 2024

My 1997 Express last summer after I performed some a/c work and a ~20 minute test drive. It was holding low 30s at 2,000 rpm. It was over 100F outside at the time.

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L31MaxExpress · Jun 22, 2024

I also tested it with the ambient air coming across the condenser right at 115F and the ambient humidity was ~20%. It was 109F officially at that time, but in the all concrete area surrounding I tested it in, was a bit warmer. At idle it warmed up to low-mid 50s. Still plenty cool in the van though because both blower fans were on high speed and the dual air does a good job moving a ton of air through the cabin. This was after swapping the underperforming Sanden for a 10 cylinder HT6. 210cc compressor displacement vs 155cc of the Sanden. Clutch fan sounded like a dump truck in that heat, moving a ton of airflow as well.

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JohnZ71 · Jun 22, 2024

L31MaxExpress said:
The compressor spinning slow is the bigger issue. Stay away from the Sanden replacement, even with the small pulley it is woefully inadequate at lower rpm. For a 96+ Vortec, the Four Seasons 10 cylinder HT6 upgrade moves a lot more refrigerant. Get one for an Express van as it has the smaller pulley on it. On the trucks, I use the larger Suburban/Tahoe dual air condenser. Have to move the mounts and get new GM cushions to fit the upgraded microtube parallel flow style condenser. On the Vortec era trucks the holes are typically already in the core support for the wider condenser. The difference is a ~27" wide condenser core vs ~34" wide core. The condenser cost about the same $ so it is a nearly free upgrade when the system is being renewed anyway. You cannot flush the condensers on these trucks as they have multiple flow paths.

The compressor is new, but i'm not sure of the brand. I know it's not a Sanden. I would hate to buy another new one just for the pulley. Do you know the size difference between the two compressor pulleys? And can i just pull a pulley off an express van and install on mine?

JohnZ71 · Jun 22, 2024

Something else i need to do is add clear ceramic tint to the windshield to block a lot of the suns heat. I have ceramic on the other windows and it was a huge difference. The windshield and dash area stay so incredibly hot.

Better AC with different size pulley?

JohnZ71

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