88-94 5.7 Suburban A/C Diagnosis and Tuning

[L31MaxExpress]

For mockup work though, I would grab a junkyard V5 or V7 off a S10. Take note of the mounting orientation. The control valve ideally needs to be in the 6 o''clock position although 5-7 would still work well. Has to sit in that ball park for oil pickup. The ac ports stand vertically at that position, hence the need to make custom lines. The port spacing and sizing is typical GM so there are many options for adapter fittings. If you look on top of that HT6 I bought a set to convert the 87 G20 to the HT6. That particular setup was a Four Seasons part number with a thick aluminum hold down and individual lines that can swivel in whatever orientation is desired.

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[Wildblue19]

FWIW my 93 has no HPCO, only a burst disc on the compressor. 94+ have the cutoff valve in the condenser, but the fittings changed to metric.

I'll try and look around locally for one to mock up. Not afraid of some custom lines but easier saves me time and money, I'm sure there's a way to make it almost bolt in. For sure I will need a high pressure port spliced in somewhere.

Take a look at this article, I found it pretty interesting. I stumbled upon it while trying to figure out what the deal is with the 5 or 6 different control valve colors for the V5/7 series. I get that the valves determine when to destroke the compressor, but as for which to choose.... I don't have an educated guess on where to start.

 

[L31MaxExpress]

FWIW my 93 has no HPCO, only a burst disc on the compressor. 94+ have the cutoff valve in the condenser, but the fittings changed to metric.

I'll try and look around locally for one to mock up. Not afraid of some custom lines but easier saves me time and money, I'm sure there's a way to make it almost bolt in. For sure I will need a high pressure port spliced in somewhere.

Take a look at this article, I found it pretty interesting. I stumbled upon it while trying to figure out what the deal is with the 5 or 6 different control valve colors for the V5/7 series. I get that the valves determine when to destroke the compressor, but as for which to choose.... I don't have an educated guess on where to start.

If you are building hoses anyway, crimp a Trinary switch into the line coming off the compressor and wire it in-line with the clutch wiring. That would also give you a way to control your pusher fan only as needed.

I would start with the 37.5 psi valve. The pressure is always going to be a touch higher at the evaporator core than the compressor. 37.5 psi corresponds with 31°F with R152a on the P/T chart. IIRC correctly the available valves are 37.5, 40, 41, 42, 43, 44 and 45 psi. Then again the cheapest/easiest starting point is whatever valve is in the compressor to start with and adjust from there if needed. I was also digging around more on the subject, a 98-03 2.2L S10 V7 has a 6 groove pulley and 4 mounting ears. The stock S10 control valve may provide acceptable results as is. Even 45 psi is ~40°F. Nearest I can tell it looks like the aftermarket is using the 45 psi control valve nearly across the board. Not an ideal situation but they will not be freezing up evaporator cores.

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[L31MaxExpress]

I also found this chart from a company that builds the control valves. I have no way to verify it is completely accurate relative to the GM valves. It is what they sell as replacements for the GM valves though. The below 30 offering would basically convert the compressor to fixed displacement by my logic.

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[Wildblue19]

Saw those charts while digging around too. I probably will start with a factory valve and adjust if it needs it.

U-pull wants 60 bucks for a used compressor. I can get a new Chinese one for 80 bucks on ebay and return it when I'm done with mockup, so that’s probably going to be my plan.

 

[L31MaxExpress]

Saw those charts while digging around too. I probably will start with a factory valve and adjust if it needs it.

U-pull wants 60 bucks for a used compressor. I can get a new Chinese one for 80 bucks on ebay and return it when I'm done with mockup, so that’s probably going to be my plan.

Sounds like a good plan. If you get lucky the radial mounting on the V7 may come very close to matching either the stock R4 pattern or the Sanden pattern.

 

[L31MaxExpress]

I keep reading that infared thermometers are not accurate for ac work. Not sure why people are claiming that. I finally had a chance to grab mine from my mom's house. I used it to check all the ducts in her house a while back. Looks like it reads the same to me. I was questioning the accuracy of the thermometer I was using given the results I am seeing. Pretty close readings between the two. Still blowing very cold.

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[Schurkey]

Infrared thermometers don't measure temperature directly. They measure infrared radiation, and that varies with the surface you're pointed-at.

The amount of infrared given off by a surface is called it's "emissivity". A matte-black object radiates differently than a shiny "chrome" surface, for example.

Most infrared thermometers are "tuned" to a general, "universal" emissivity setting, some have adjustable emissivity--but then you have to know the emissivity of whatever you're testing.

 

[Wildblue19]

I've also noticed that the ambient air will affect my (cheap) infrared gun readings. If there is a cool breeze directly on the sensor, the readings will drop as the sensor itself cools.

I bought my IR camera to help combat this, where you can actually see that the shiny surfaces have a wacky pattern vs a matte area based on the emissivity. Mine also will auto scale the emissivity, and usually is within a couple degrees. For plastic, it is fairly consistent but on metals I almost always put matte painters tape on the surface to get repeatable measurements.

 

[L31MaxExpress]

I put 50 miles on the van each way going to Lowes for some materials for the bathroom remodel at my mom's house. It was 72° and 76% humidity. Tested the low pressure cutout setting. It never froze up the evaporator, but I know that I am on the ragged edge of the system doing that. This is where it cools to prior to cycling the compressor.

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