1991 Suburban HVAC Questions

[busterswt]

Hello all,

AC compressor recently started making some noise which quickly pivoted to locking up when turned on. The pulley still turns freely otherwise. The clutch looks toasted (see pics). Given the compressor looks to be the original and has had some green dye or stop leak through it already, I decided it's probably more cost effective to replace the compressor and associated parts than to try and replace the clutch and bearing, only to then have to replace everything, anyway. This system had been converted to R134a at some point in its life.

That said, folks seem to be split on an R4 versus Sanden replacement. Would rather keep it close to factory, if possible, so I'm looking at the following:

AC Delco R4 (NEW) 15-20185:- R4 w/ Clutch R134A Retrofit; Air Conditioning; Manual Controls(C60)

I'll be replacing the condenser, too, but am split between the Spectre 7-3642 and AC Delco 15-6960. I understand either will require some slight modifications to get mounted. Can I go wrong with either one?

Lastly, I wondering if mounting the pusher fan from a 454 would provide any additional benefits. Not sure if the core support has any provisions for that, but it looks fairly straightforward nonetheless. That part is Four Seasons 75751. Has anyone done that mod?

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1991 Chevrolet Suburban V2500 4x4 5.7L TBI

 

[quaddriver]

i just did mine, only diffs where mine is a 90 and my engine is a 454 - the hoses appear to be different. OTHERWISE, they are being made new, but not GM (specifically harrison) any longer and you want it as NEW as in modern as possible to get the right seals.

if your condenser is not holed, buy a wash kit or borrow one and flush it well and blow it with air a LOT. Since it is (should be) a series tube cooler, this will work. IF you buy a new parallel condenser it can never be cleaned out.

At this point in your game the most important thing is getting rid of any debris and all 'goo', change the receiver dryer and orifice. buy the GM numbered seal kit and use THAT, it has been my experience the seals are slightly superior. if it makes you feel better, for $10 buy the UV dye from harbor freight and dump a wee bit into the condenser before you pull a vacuum.

Note: unless you have rear AC, you do NOT have a thermal expansion valve so avoid the kit that contains one for unnecessary cost (if you can - some just toss it in). The UAC, GPD and or four seasons products dont suck. You CAN rebuild the old compressor, BUT if its locked it might have a mechanical jam in there and it really cannot be re-machined.

additional concerns: if you are changing from one technology to another, i.e. series vs parallel evap or condenser, you really need to change BOTH. they have to be sized to each other (has to do with the ideal gas law - its technical) and if not the volume ratios change and ergo the temp ratios change and it might not cool as well. (consider your HS physics lessons on 'PV=nRT'.) You WILL note a change in efficiency going R12 to R134a. If yours truly is a virgin, the R134a is not as efficient as the R12 in the FACTORY sized stuff, to overcome R134 not being as 'nice' as 12, they just increased the cooling area in later years. For our squares, its not as ice as ice so to speak. but its ok. my square is mostly a show truck, not a grocery/plywood getter so hot summer lowes parking lots dont worry me.

follow the instructions (just ask) INCLUDING dumping out the shipping oil and refilling with NEW PAG. you can re-use the shipping plug to hold it all in one place while you fiddle. just be sure you use the correct compressor seal set depending on actual stuff in place, i.e. do you use the stepped red/green vs gold or silver seals? most kits ship em all.

ps: the spectra premium stuff does not suck at all. good canadian company and I have been using their replacement metal (coolers, tanks etc) for decades with good results'

 

[Finkaire]

Refill with “Ester oil” for a retrofit system. PAG oil is a corrosive and may take out your factory evaporator. Also the orifice tube may be located in the condenser if a single system.

 

[busterswt]

if your condenser is not holed, buy a wash kit or borrow one and flush it well and blow it with air a LOT. Since it is (should be) a series tube cooler, this will work. IF you buy a new parallel condenser it can never be cleaned out.

The original finned tube condenser is still installed. I don't think its damaged or leaking, and I'm happy to continue using it as long as a flush is effective. I keep hearing the parallel flow is better suited to R134a, but if we're only talking about a few degrees difference in temperature after all said and done, I'd rather save that job for another time. Anyone able to quantify the difference between the two?

At this point in your game the most important thing is getting rid of any debris and all 'goo', change the receiver dryer and orifice. buy the GM numbered seal kit and use THAT, it has been my experience the seals are slightly superior. if it makes you feel better, for $10 buy the UV dye from harbor freight and dump a wee bit into the condenser before you pull a vacuum.

Note: unless you have rear AC, you do NOT have a thermal expansion valve so avoid the kit that contains one for unnecessary cost (if you can - some just toss it in). The UAC, GPD and or four seasons products dont suck. You CAN rebuild the old compressor, BUT if its locked it might have a mechanical jam in there and it really cannot be re-machined.

I do have rear A/C in this Suburban and plan to replace the expansion valve at the same time.

additional concerns: if you are changing from one technology to another, i.e. series vs parallel evap or condenser, you really need to change BOTH. they have to be sized to each other (has to do with the ideal gas law - its technical) and if not the volume ratios change and ergo the temp ratios change and it might not cool as well. (consider your HS physics lessons on 'PV=nRT'.) You WILL note a change in efficiency going R12 to R134a. If yours truly is a virgin, the R134a is not as efficient as the R12 in the FACTORY sized stuff, to overcome R134 not being as 'nice' as 12, they just increased the cooling area in later years. For our squares, its not as ice as ice so to speak. but its ok. my square is mostly a show truck, not a grocery/plywood getter so hot summer lowes parking lots dont worry me.

Good to know. Hadn't really seen anyone mention changing the evaporator(s) style along with the condenser. This 'burb had been converted by the previous owner at some point in time, but I have no idea what was changed or if it had been done correctly. It does appear to be the original compressor (if labels are anything to go by). There was definitely evidence of UV dye having leaked out around the compressor, but it looked like it had been there a while. When I bought the truck there was no charge and the rear A/C fan motors were non functional. Replaced front and rear fan motors along with some resistors, vacuumed and charged, and we were good to go for nearly a year.

follow the instructions (just ask) INCLUDING dumping out the shipping oil and refilling with NEW PAG. you can re-use the shipping plug to hold it all in one place while you fiddle. just be sure you use the correct compressor seal set depending on actual stuff in place, i.e. do you use the stepped red/green vs gold or silver seals? most kits ship em all.

Good call. Will pay close attention to this.

ps: the spectra premium stuff does not suck at all. good canadian company and I have been using their replacement metal (coolers, tanks etc) for decades with good results'

Have used Spectra in the past with good success. If folks are upgrading to a parallel flow condenser, I'm curious if there's a preference for Spectra 7-3642 or AC Delco 15-6960.

 

[busterswt]

Flushed the evaporators and am looking to button things up, but before I do I need to replace the oil in the system. The service manual has the following:

- Oil -

Rear Interior (C69) System
R/V (with R4) ......... 9 ozs.

That should be the same for mineral oil or pag, right?

It mentions the following for refrigerant:

- R-12 -

Rear Interior (C69) System
R/V (with R4) .... 4 lbs, 8 ozs. (72 ozs.)

I've seen mention of 75-80% R134a to 100% R-12, so does a good starting point of ~ 3 lbs, 6 ozs (54 ozs) sound reasonable?