AC overhaul - Compressor upgrade? Condensor?

[L31MaxExpress]

That is the R134a thread 36496 and 37219 installed on my 97 Express. Wiring and splices split loomed. At the time I used solder sleeves and wrapped those in Tartan tape to further protect the splices.

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[PlayingWithTBI]

That is the R134a thread 36496 and 37219 installed on my 97 Express. Wiring and splices split loomed. At the time I used solder sleeves and wrapped those in Tartan tape to further protect the splices.

So, the original connector won't work? I need to replace it?

 

[L31MaxExpress]

So, the original connector won't work? I need to replace it?

Looks like 88 used the older style switch and 89+ the newer style if RockAutos catalog can be trusted. So you may very well be able to use your stock connector. If your 88 has the larger footprint adjustable switch the replacement switch will plug right in.

 

[L31MaxExpress]

So, the original connector won't work? I need to replace it?

This is the style switch I have seen on every GMT400 I have worked on. However I do not remember ever having worked on a 1988 with AC. The one I worked on years ago was a non AC truck. I remember that one because it had a real oddball of a 4 rib serpentine belt and a 3 bladed engine fan on its 305. I had to swap the alternator pulley on the alternator I installed on it because nobody had a 4 rib pulley on the replacement unit.

My 97 Express and 99 Tahoe both had this garbage, failure prone switch on it from the factory and so did my buddies 2003 GMT800 1500 HD. His was cycling at 60 psi and would not get below 60F or so at the vents before cutting the compressor. Swapped to the adjustable switch and he was in the low 40s, upper 30s driving around on a 105F day.

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[PlayingWithTBI]

Looks like 88 used the older style switch and 89+ the newer style if RockAutos catalog can be trusted. So you may very well be able to use your stock connector. If your 88 has the larger footprint adjustable switch the replacement switch will plug right in.

Yeah, I seem to remember seeing a screw head in between the connector lugs. I may need to play with it and see if I can get lower pressure shutoff. Right now, when it's ~120° ambient, I'm getting ~44 - 46° with the 11 blade fan, parallel flow condenser, and the pusher fan I recently installed. I mean it's adequate in my Regular Cab but, I WANT MORE!

 

[yevgenievich]

Sounds like the cycling switch may be cutting out too early. I have seen numerous examples of the stock switch start cutting out the compressor as early as 60 psi and cooling drastically suffers. Change the switch and the systems will go right back to cooling correctly. I carried a spare stock switch in the glovebox of my Express van for years as it failed more than once. Then I found the R134a thread older style adjustable switch. That switch is still living over 10 years later. I would fit it with an adjustable switch myself and dial it in to cutout just before the evaporator core freezes into a solid block of ice. I checked the 87 G20 van the other day and the cycling switch is cutting the compressor at 18 psi on it. 18 psi is equivalent to the refrigerant boiling at 25F. R134a would need to cutout at 21 psi in theory. R152a has nearly 2x the latent heat of evaporation of R134a requiring substantially less refrigerant to do the same work in the evaporator core.

Four Seasons 36496 is the R134a thread adjustable switch and it is calibrated at 22 psi out of the box. OE application includes a 1994 G10/20/30 van. 37219 is the connector replacement for that switch.

I need to change my switch out to adjustable for sure, lately I have it bypassed as it was acting up. Will run more tests at a later time to pin point where my issue is. But compressor change it self was a win.

 

[L31MaxExpress]

Yeah, I seem to remember seeing a screw head in between the connector lugs. I may need to play with it and see if I can get lower pressure shutoff. Right now, when it's ~120° ambient, I'm getting ~44 - 46° with the 11 blade fan, parallel flow condenser, and the pusher fan I recently installed. I mean it's adequate in my Regular Cab but, I WANT MORE!

Lowering the cutout only results in cooler air if the system is capable of reaching the current cutout resulting in earlier than necessary cycling of the clutch. If it still has the R12 cutout pressure around 28-30 psi it is likely that it does cycle out earlier than it could. I have killed a couple of those older switches adjusting them with R134a conversion, the 87 G20 was no exception. Thought the old one might survive but it did not. Honestly cannot explain why turning the set screw on an older factory switch that is working kills it.

 

[L31MaxExpress]

I need to change my switch out to adjustable for sure, lately I have it bypassed as it was acting up. Will run more tests at a later time to pin point where my issue is. But compressor change it self was a win.

Well if it is bypassed the cutout pressure should be irrelevant. It is possible however with the switch bypassed you are freezing the evaporator core and losing airflow through it and heat transfer. Then when you slow down the low side pressure rises enough to allow the ice to melt restoring cooling. When the stock front evaporator core in my 97 plugged up with organic material, the blower forcing air into the cores restriction actually blew out the aging/crumbling foam sealing strips between the core and housing and airflow was bypassing around the core rather than going through it. Resulted in a dramatic loss of cooling although the vents still blew decently just not cold. When I put the new core in it with new sealing strips ot started cooling like it should have.

This is what the 97s core looked like in 2011. I fixed the AC in it in summer of 2011 because my dad dying of pancreatic cancer was more comfortable riding around in the van than the other vehicles and was not able to handle the summer heat well at all with the illness, chemo and pain meds they had him on. The van only had a little over 65,000 miles at the time.

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Most of the debris in that core can be blamed on parking in the driveway in the shadow of this huge Sycamore tree in my parents backyard. The stuff fell everywhere including down the cowl vent air intake. The 1983 G20 had the same issue too. The fuzzy looking stuff and those little spear looking things come off the seed pods. They explode when they hit the ground. The spears are the perfect size to get stuck in between the fins of the evaporator core. Then they get wet and swell and there is no getting them out.

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[L31MaxExpress]

The 87 G20 had the same problem. Parked under trees for years. Not the same type of trees but the same result. Explained why I was not able get good results when I attempted to charge the untouched system a few years prior when the 305 was still running in it. I have since learned to check the evaporator core or cabin filter if equipped first. That collection of debris was covering a solid 1/2 of the evaporator core.

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Neither my brother or sister ever have cabin filters replaced. My sister was here last summer and my poor nephew was about to fry in her 2014 Silverado crew cab that is black on black leather. I pulled the nastiest cabin filter out of it that had to have been 140K mile OEM. It also had never had the refrigerant level even checked in it. Ended up putting a whole can of R134a into it to get the system cooling well again and the pressure where they needed to be. Needless to say little fellow did not bake in his car seat on the way home. My sister said she would have had both done had anyone suggested it and and had actually had the ac system "checked". Apparantly the shop jammed a thermometer in the center vent saw it was cooling 60F on 110F day and said it was all it would cool. When she drove away after I worked on it, it was in the low 40s and blowing twice as hard out of the vents. At 60F it was not even cold enough to drip moisture out of the HVAC case. When I finished charging it, it was pouring water on the ground. Even a system that is not technically leaking will lose a good 1/4 lbs a year out of the compressor shaft seal if not more. In 4 years that system has lost 1 lbs. My local Oreilly luckily had a brand new gauge set still wrapped in plastic as one of their rental tools that they let me borrow to charge the system up in their parking lot when I bought the R134a. I knew the manager from managing a store in the same district prior so that helped.

This was a 100K or more cabin filter. Ford came out with a cabin filter in 1985 in the Taurus. It is absolutely stupid that penny pinching bean counters at GM rarely use them. Even many brand new GMs do not have them. All this trash goes right into the HVAC case as a result.

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[BowhunterBrown]

Great stuff L31ME!

I had a little time yesterday and today to work on the AC. I had my neighbor with the machine pull the refrigerant yesterday. He recovered roughly 64 oz which is spec for this suburban, so that was good. I still replaced the high pressure valve.

1) I slapped on the four seasons compressor 88947 with the smaller pulley. Luckily happened to have a slightly shorter belt that fit perfect. The compressor case looks same size as the Delphi I pulled. But it is larger 210cc capacity?

2) I swapped in the Boxi parallel flow condenser (Part number in my last post) It was a good stock fit.

3) I swapped in a fixed 0.062 orifice tube.
The one it replaced was preinstalled in the new UAC refrigerant y-line I installed with winter overhaul. It appeared to be slightly smaller orifice than the 0.062" fixed that is now installed.

Pulled a vacuum for over an hour to draw out any moisture. Held vacuum perfectly for over an hour. Looking to recharge tomorrow. Just need to decide on putting r134 back in or giving the r152 a shot. I will probably just have r134 put in for now just to limit the variables. I should have case of r152a, side canister tap arriving in next day or two. So if the system is still not up to *****, I will consider trying r152a.

I haven't installed the pusher fan. Looks like I will have to relocate the trans cooler or the engine oil cooler to make the aux fan fit. That will have to wait until winter.

I do have that adjustable low side cutout switch on hand (and connector), and have not installed that yet. What's a good way to determine what pressure current stock switch is cutting out at? Same question for high side cutoff switch? Is there a test with gauges or ??

AGILITY​

7010190

Lastly, the Agility 7010190 condensor arrived today. It is the late model Tahoe one L31ME recommended. It is a little big. At 18" tall some modification of the rad support would have to be done. The generic line fitting adapters did not fit so I settled on the stock size Boxi condenser. The Agility 7010190 looks like it would definitely perform well with its large size and subcooler, but it looks to require 1) rad support modification, 2) possible hard to find adapter fittings 3) custom lines to and from condenser as the width puts the fittings past stock location up tight to the passage hole on the rad support. It could be done, but if there was a similar condenser out there 10% smaller in width and height.