Automotive Air Conditioning Information Forum

Hello,

Long time lurker and hoping I can find some information. Looking for a performance chart for the GM 10S20F compressor used on the trucks and vans. I have a friends 2012 Express Explorer conversion van that I am working on that has had 65-70°F vent temps at idle and only modest improvements in cooling at 70 mph on the highway since it was new. He recently asked me for help with it after having a GM dealership insist that it had a failing compressor and charged him nearly 3K in parts and labor only to end up with the same poor cooling. After performing the work they now claim it has acceptable cooling for the ambient conditions.

I own a 97 Express conversion that cools much better with a HT6 and now a Four Seasons 88947 HT6 replacement. You could hang meat in the 97 on 110°F Texas summer day. Same for my 83 conversion that used the old A6. With the A6 and the largest parallel flow I could fit in the grille opening on the 83, it blew ice crystals out of the vents at idle. That 83 still cools well with the Valeo HT6 replacement when I put an 8.1L into it.

I have checked the common stuff on the 2012. The low side pressures are high especially at idle. Fan clutch has been replaced with the OE towing unit, the condenser is a new GM and clean. The compressor was replaced 6 months ago with a new GM compressor. The system was flushed, both the expansion valve and orifice tube were replaced. The condenser and accumulator were also replaced. The dealership added a GMT400 pusher fan in the same manner as the GMT800 poor idle cooling TSB. I checked the pressures and temperatures and even misted the condenser with minimal improvements. I evacuated the system, installed a Red Ford 0.062" front orifice (which I have used for years in both my G20 and Express vans with rear ac) which provided a 3-5°F temperature reduction. However the suction side is still around 60-65 psi idle and 50 psi at 2,000 rpm. The high side never breaks 275 psi and dropped under 200 psi misting the condenser which only reduced the low side pressure an additional 5-10 psi. Long story short I believe the 10S20F is simply not keeping up with the evaporator load. I am considering replacing the 10S20F with a V7 for a LS1 Camaro and building lines for the setup. I have the chart for a V7 and before I attempt the V7 swap was hoping to find the 10S20F chart for a sanity check to see if the V7 would be an improvement. I know these vans can cool exceptionally well with dual air and all indications point to the compressor being the weak link but I want to confirm that diagnosis. I know the V7s can move some serious BTUs and the fact they do not have to cycle makes them cool very well. I have swapped the older S10 V7s into a couple of dual air R4 systems with great results.

70 f and no better? With a wet condenser?

Have you checked for reheating? Your pressures indicate it is moving some heat - 275psi @ 110f ambient is what I piece together from your post.

Start with a full load test. Cabin fan on highest speed. Front doors open. Engine RPM above 1800 rpm for at least 90 seconds to stabilize.

Record the high and low side while above 1800 rpm. Record the ambient temperature and vent temperature, humidity too.

Post them up

70°F dry with the 0.072 orifice, dropped to 65°F with the Red Ford orifice tube. Got down to ~60°F misting the condenser pretty heavily.

No reheating going on. I pinched the heater supply hose off at the water pump heater outlet prior to starting the engine. Recirculation door closes minus the 1" wide strip GM left open to outside air.

Already did the full load test prior to touching anything. It was 108°F and 18% RH. Engine at 2,000 rpm via bidirectional control on a scan tool, best it had was 70°F. Fan clutch was engaged and moving a massive amount of air. Pressures were 275/65. Misted the condenser, 200/50 and about 60-62°F. After 30 minutes of open highway driving at 70-80 mph it struggles to get to 55°F.

Charge is correct per the label added for the rear ac system.

The FSM will have a chart with some wide ranges based on ambient temperature and humidity. Probably why the dealer says it is good enough.

It does sound like the system is short on capacity. Does it do any better from the dash vents with the rear system shut down?

I am puzzled by the relatively low High side pressure under a full load test at those temps. I would have expected around 300 psi. Since the problem persists with a new compressor, we can rule out a weak compressor. And this is not a common complaint with that vehicle here in Las Vegas

I think I would take the Plateau approach and cautiously add some refrigerant. Monitor the pressures and vent temps with a 1500+ rpm engine speed. Add small quantities of refrigerant and wait 30 seconds to stabilize. Watch the high side pressure, and make sure you don't go past 3x the ambient temperature
For example 3x 108f = 324 psi

bohica2xo wrote: ↑Mon Sep 11, 2023 7:46 pm The FSM will have a chart with some wide ranges based on ambient temperature and humidity. Probably why the dealer says it is good enough.

It does sound like the system is short on capacity. Does it do any better from the dash vents with the rear system shut down?

I am puzzled by the relatively low High side pressure under a full load test at those temps. I would have expected around 300 psi. Since the problem persists with a new compressor, we can rule out a weak compressor. And this is not a common complaint with that vehicle here in Las Vegas

I think I would take the Plateau approach and cautiously add some refrigerant. Monitor the pressures and vent temps with a 1500+ rpm engine speed. Add small quantities of refrigerant and wait 30 seconds to stabilize. Watch the high side pressure, and make sure you don't go past 3x the ambient temperature
For example 3x 108f = 324 psi

It has a 3° of so difference turning the rear blower off. I pinched off the small rubber section of the high side liquid line to the rear unit and saw about the same change as turning off the blower.

I have played with the charge 8 oz in both directions with the specified amount giving the best results. The low side pressure increases if I add or remove more than about 2 oz.

The 300+ high side pressure does not seem typical. I have an 97 Express and it does not run over 280 psi on the hottest days.

Interesting.

How does the rear evaporator perform? Vent temps?

300 psi on the high side is common here on a 10 year old vehicle at 108 - 110 f.

We call 108f "9am in Havasu". Our goal is to keep the high side under 400 psi in Death Valley.

.

Some additional thoughts...

A low-side pressure of around 50 PSI at 2,000 RPM correlates to an evaporator temperature of ~55°F, much too warm for a comfortable cabin, especially at 100°F-plus ambient temperatures. The elevated low-side pressures you're seeing seem to suggest an OT problem—an orifice that's too big, a missing internal brass tube, or leakage around the body of the OT. I'm presuming that this is not a variable OT.

A few questions: Is the OT installed in the right direction? Does it have all its o-rings in place? Is the metal tube into which the OT fits bent, crimped, or otherwise deformed? Did you examine the existing OT closely to ensure that the internal brass tube is present? Have you tried another OT of the same design and color? New doesn't always mean that a part is any good.

bohica2xo wrote: ↑Tue Sep 12, 2023 7:16 am Interesting.

How does the rear evaporator perform? Vent temps?

300 psi on the high side is common here on a 10 year old vehicle at 108 - 110 f.

We call 108f "9am in Havasu". Our goal is to keep the high side under 400 psi in Death Valley.

.

Rear unit cools close to the front, maybe 2-3°F cooler.

10 year old vehicle but one that has a massive new condenser and clutch fan on it. I should also add that I added strips of closed cell foam insulation between the radiator and condenser and the shroud and radiator. It is a 10 minute job that tends to help idle cooling.

I know the feeling on the temps. It was 100F by 8am here multiple times and we had a few days top 115F.

JohnHere wrote: ↑Tue Sep 12, 2023 9:01 am Some additional thoughts...

A low-side pressure of around 50 PSI at 2,000 RPM correlates to an evaporator temperature of ~55°F, much too warm for a comfortable cabin, especially at 100°F-plus ambient temperatures. The elevated low-side pressures you're seeing seem to suggest an OT problem—an orifice that's too big, a missing internal brass tube, or leakage around the body of the OT. I'm presuming that this is not a variable OT.

A few questions: Is the OT installed in the right direction? Does it have all its o-rings in place? Is the metal tube into which the OT fits bent, crimped, or otherwise deformed? Did you examine the existing OT closely to ensure that the internal brass tube is present? Have you tried another OT of the same design and color? New doesn't always mean that a part is any good.

I know what I would do if it were my van and I were the only one that would ever work on.

The GM White tube had the oring and brass tube in place and it is in the correct orientation. I have never had great cooling with that tube in Texas heat and humidity. GM definitely missed the OE orifice tube sizing here.

I replaced the GM White 0.072" tube with a Ford Red 0.062". Both orings were on it and it had the brass tube in place. Cooling is a bit better with the Red tube. I would love to mess around more with it, but it is 76F now and will be for atleast a week.

My next step was going to be to verify the compressor clutch/belt is not slipping using a non contact tachometer on the clutch hub. I noticed in my temperature measurements the clutch pulley was much hotter than the compressor. No odd noises to make me believe it was slipping, but it was odd that the hub was 50°F hotter than the compressor body.

In that case measure the clutch air gap with a feeler gauge. Should be about .020