‘91 Suburban A/C Cooling Help

Ok so I went for a ride, mostly 45-65 mph, few stops but not for long. Dash vents I saw a low of 45 and rear just above 50. Granted it’s night time, it’s raining, and ambient temp is about 78, it was getting cold inside. Parked and let the truck idle for a 15 minutes or so and crept up to the same as before, mid to upper 50s.

I swear I had a wiff of Freon after shut down by drivers side head light where condenser sits. I’m thinking condenser based on that and the fact that I got a solid drop while driving. I should have enough air flow with the electric fans to maintain temps at slower speeds/stopped. What say you? They will literally suck this piece of foam through the air, I’m holding it and the fan suction is keeping it suspended:

measure the ambient temp in front of the truck. in my limited AC experience on my burb, the engine really puts out a lot heat and the ambient temp around the engine bay might be 90-100 deg when it is 78 deg outside...

I didn’t measure temp at the front of the grill, but with the amount of air flowing in, it did not feel any warmer than ambient.

yevgenievich said:

I found parallel flow condenser along with red orifice tube to be helpful. Also seal sides of rad and condenser so air is pulled through and not around. Additional insulation on accumulator and cold lines.
Which sanden did you get?

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Do you remember the part number of the parallel flow condenser you used? I found AC Delco number 52484151, but they do not appear to be available other than Chinesium versions.

91burb2500 said:

Do you remember the part number of the parallel flow condenser you used? I found AC Delco number 52484151, but they do not appear to be available other than Chinesium versions.

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The one I used came from oreily back in 2015, but they appeared to have switched suppliers as the one currently shows up has reviews of being too narrow.

They all appear to be a little narrower, guess I’ll have to order one and see what comes. This one crosses to the ac delco one and appears to be a parallel by the photos: https://www.ebay.com/itm/1562063608...O6SYSwPTx2&var=&widget_ver=artemis&media=COPY

I did a little research on your issue and was looking at displacement on compressors. The 508 is an 8.4 cubic inch compressor. The R4 you took off comes in at slightly less than 10 cubic inches. You didn't say how good or bad the system worked before converting to the 508 so I'm going to guess it worked good. The 1.5 or so cubic inches you gave up in the swap is why the system now won't cool properly. When you drop cubic inches, the compressor is now undersized to the rest of the system or you can look at at it as the rest of the system is oversized for the compressor. Also, you didn't say if you were using reman R4's or new. Never use a reman R4, they don't last. If you didn't have the rear a/c the 508 would work fine. To make the system work right again, a compressor change is needed. I've worked on a/c systems since 1987 and spent 25 years at a school district as a mechanic which included a lot of a/c work on buses and support vehicles before retiring and I've seen a lot of weird issues with a/c systems.

Pressures look to be in the ball park for 134a, dumb question, do you know that your blend door actuator is fully closed when you select full cold? Those actuators go bad and may be hung up keeping hot air flowing in the cab. They are pretty easy and cheap to replace too. I just redid my AC under the hood on my 94 (without getting into the dash condenser and evap valve) and so far so good. Followed Suburban Ranch YouTube video.

When I was rummaging around under there (trying to get ECU part numbers) it appeared as though the blend door (at least on my 1989) is operated by cable - and the diverters that send the air either to the degoggers, chest-level vents or floor vents are vacuum operated. My blend door most certainly does not fully seal off - I get discernable heat in the winter while having the controls set to vent only and full cool. That does impact how cool the A/C can get in the summer...I've wondered if it would actually harm the engine to put a heater control valve in, or would just using a heater core bypass in the summer be better?

YakkoWarner said:

When I was rummaging around under there (trying to get ECU part numbers) it appeared as though the blend door (at least on my 1989) is operated by cable - and the diverters that send the air either to the degoggers, chest-level vents or floor vents are vacuum operated. My blend door most certainly does not fully seal off - I get discernable heat in the winter while having the controls set to vent only and full cool. That does impact how cool the A/C can get in the summer...I've wondered if it would actually harm the engine to put a heater control valve in, or would just using a heater core bypass in the summer be better?

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Even with the blend door all the way closed, there is still a lot of residual heat build up in the core and the hvac box. Vent setting cruising down the highway I see at least a 5 degree bump in temp from outside to vent. I've thought about installing a couple ball valves and a bypass, but was worries about the core sitting with the same coolant in it all summer and something corroding or otherwise creating a leak.

With real coolant I don't expect it would do any harm - I've found radiators in the scrapyard that were still clean inside after years as long as they had actual coolant (for corrosion inhibitition). I'd be worried about galvanic actions of using valves that may not be the right metallurgy - I knew someone when I lived in Virginia who dissolved a BMW engine from the inside out by using a hardware store coupling in one of the coolant lines...dissimilar metals can cause weird arcane actions explainable only by advances chemists and/or voodoo practioners. I was thinking about something like one of those plastic fluxh/fill fittings you see at the parts stores. I had to use one on an early 90's Ford that had a core failure, but in that case both heater hoses were the same size. GM used slightly different sizes which means a generic fitting like that will probably not work....

The R4 that came on the truck was a parts house turd, replaced with a new AC Delco as was the next one. System worked no better with the R4, possibly worse but that is speculation on my part as I never measured temps with that one.

Had a mechanical fan originally but it didn’t sit in the shroud right since it was a big block shroud. I wired up the pusher fan on the front to a relay triggered by the compressor instead of temp. That helped, so i ended up going full electric fans and that helped too, but just couldn’t get any really solid vent temps when not rolling down the highway. I checked again and for sure I smell Freon on the drivers side when I shut the truck down and the fans stop pulling air in, so either way that condenser has got to go. Hopefully that makes it happy, dropping it off Friday to get it vac’d, swapped and recharged.

The ball valve is a bronze valve with an isolated stainless ball, we use them in saltwater and they don’t seem to have any issues with galvanic corrosion. There is coolant in the system too, not just water. I have a loop fitting with the right 5/8 to 3/4 nipples on it I could throw in for ***** and giggles. My blend door is cable operated, I checked in when I replaced the core and it had good rubber and closed well.

SD7H15 is better match for the size of the system.
I believe 250cc oil for dual system it was. When I redid my system I flushed everything, replaced rear tx valve and filled fresh to be sure how much oil is in the system.

Edit:
Posted service guide here before.

Happy to report that the parallel flow condenser made a world of difference. The eBay link posted above was the unit that was installed. I got to the truck after the shop swapped it out and it was sitting in the sun. Within a couple of minutes of driving, my vent temps were in the upper 50s, stop and go traffic for about a 5 mile ride and it stayed consistent, would drop into the low 50s driving at 50-60 MPH for short bursts between lights. Currently 92 degrees outside with 60% humidity. Thank you to all who provided advice and direction, I would say it is safe to assume that the parallel flow condenser is a must with the R134a freon. Now I need to get my vac acutator working for the floor/dash blend so I'm not wasting so much air cooling the carpet.

91burb2500 said:

Happy to report that the parallel flow condenser made a world of difference. The eBay link posted above was the unit that was installed. I got to the truck after the shop swapped it out and it was sitting in the sun. Within a couple of minutes of driving, my vent temps were in the upper 50s, stop and go traffic for about a 5 mile ride and it stayed consistent, would drop into the low 50s driving at 50-60 MPH for short bursts between lights. Currently 92 degrees outside with 60% humidity. Thank you to all who provided advice and direction, I would say it is safe to assume that the parallel flow condenser is a must with the R134a freon. Now I need to get my vac acutator working for the floor/dash blend so I'm not wasting so much air cooling the carpet.

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I've messed with mine a bit, and i think the door is warped. So the vent settings are more like bilevel. Bilevel is like 75% floor. For AC, having a vent/floor split really is OK as it cools off high and low up front and the rear comes in high from the back. On heat, it seals up tight and only comes out the floor.