AC repair/overview on a 30 year old truck

[SAATR]

@351FUN

If you intend to R&R all these components yourself, take note of this:

One of the functions of the receiver/drier is to remove moisture from the system, as the name implies. To do so, it has a bag of desiccant (think of the silica gel packets you find in certain food packaging) in its base that will filter small amounts of water from the refrigerant. This should be one of the last components you install on the system prior to sealing it, to prevent the desiccant absorbing large quantities of atmospheric moisture and becoming useless. This is doubly true when working with R134a systems, because of the use of PAG oil.

PAG oil is extremely hygroscopic, meaning it absorbs moisture from it's surroundings very quickly. Leaving an R134a system open for any length of time in a humid environment opens up the probability of the PAG absorbing water. So your best bet is to assemble the system as quickly as reasonably possible with a new receiver/drier and fresh oil, and then to pull a long, deep vacuum to vaporize and remove as much of the moisture in the system as possible. This means, ideally, a minimum of two hours at a 29inHg vacuum or more. Below 500 microns, if the machine has a micron gauge. This will remove as much moisture as possible and leave the drier desiccant with plenty of reactivity.

If you use double end capped PAG, it is far less hygroscopic and presents less of a concern for moisture absorbtion, but the concern over the drier remains.

 

[east302]

My advice would be to replace everything except the evap behind the dash. Get new pressure sensors w/ propper R134 calibrations, condenser, compressor, dryer, o-tube, lines and o-rings. Splurge and buy the AC-Delco o-rings for the back of the compressor. RockAuto has a great breakdown and choices for everything you need. You could even get everything purchased and installed DIY, but leave the evap open. take it to a shop and ask for an evap flush, evac/leak test and charge on the system. This way you dont have to buy any HVAC tools and you save the labor for part swapping.

Adding to the above and if you have the desire, the air box dampers are likely rotted along the edges, allowing air flow to pass by. I’d guess that the 88-94 is comparable if not identical, but pulling the dash and replacing the dampers in the box made a big difference on my 98s. There are three on the left, one at the heater and one for recirculation - those last two being “why not” kind of things since you have it apart.

Summer sucks in Mississippi when all of the cold air is leaking out into the floor vent instead of going to the dash vents. Something to keep in mind.

 

[1998_K1500_Sub]

... take note of this: PAG oil is extremely hygroscopic, meaning it absorbs moisture from it's surroundings very quickly. Leaving an R134a system open for any length of time in a humid environment opens up the probability of the PAG absorbing water.

Building on @SAATR's remarks, when you assemble the system use new, sealed bottle(s) of PAG.

I'm not sure how long PAG remains usable after it's been unsealed (but still "capped") in its bottle. In my particular case I don't use PAG often, so I toss whatever is left once the job is completed.

If you use double end capped PAG, it is far less hygroscopic and presents less of a concern for moisture absorbtion, but the concern over the drier remains.

I use the double end capped PAG whenever I'm re-building an entire system with all clean parts and new oil. It's a few dollars more expensive but insignificant in the total cost of parts (I last paid $10 for 8oz, but likely higher now).

But does it matter? Do the OEMs care? My Honda's Denso compressor specifies Denso ND-8, which Denso states is double end capped (attached). Ditto for my Toyota, which specifies ND-8 in the factory service manual. So I used ND-8 when I replaced the compressor on the Honda and the condenser on the Toyota.

So for a few dollars I'll gamble on double end capped PAG.

See the paper from Purdue University I uploaded earlier in this thread, which noted:

"Critical difference in respect to hygroscopicity, anti-corrosion
performance and lubrication was observed. The double end
capped PAG out performed the single end capped PAG
with respect to all differences."​

 

[GMCTRUCKS]

Truck as a 1992 Blazer. I'm looking to get my a/c working again and have had quotes from $750-1500, with my trusted shop saying to expect it to keep climbing as other parts fail. The previous owner told me the compressor needs to be replaced. The plug for the compressor is gone. There is a paper clip cheating the high pressure switch on. On top of that it's R12, so it needs to be converted. I don't have any of the tools for the pressure side of the system, but parts changing is cake. I do industrial mechanical/electrical/fabrication for a living and have done engine swaps, but I have zero HVAC experience. If I were to tackle this myself, what parts would I want to get and what needs to be changed? I could probabl save some money doing the mechanical bits and then bringing it to a shop, but I really don't know what's there past the compressor. Or even which compressor to get from Rock Auto.

I heard there is newer O-Rings or newer than what’s on it that are better I think they are green in color.

I’m needing to replace a O-Ring on my evaporator it’s leaking oh it’s on my 93 GMC truck. Good luck

 

[Eveready]

I have just been through this with my '93. I can certify 2 things. 1 is that you will get excellent info here. 2 The job is a monumental pain in the ass and likely to fail. The best bet is not to DIY it. Just budget a grand and take it to a reputable shop that will put up with you bringing it back a few times til they get it right and it quits leaking.

Been there, done that, and have a closet full of T shirts. Go spend your money. Having it done right is worth it. Face it, that '94 will haul anything a new one will haul, is as fast or faster and with the AC, just as comfortable on a 104 degree day. You just saved about 60 grand or more at today's prices. Spend the grand and enjoy the cool.

 

[1998_K1500_Sub]

I sure wish I could weld. I was just looking at the nice job @Erik the Awful did welding his own exhaust system. D@mn that looks pretty...

350 Vortec Headers and exhaust

I want to say “maybe no” on this. Someone here tried it the other way (putting a Vortec Y-pipe on a TBI) and it was off at the header flange though you wouldn’t think that it would be. @DerekTheGreat was the guy that did that, maybe he could chime in. Here’s his thread, maybe it will help...

www.gmt400.com

I had never worked on an AC system until maybe 15yrs ago, but I had wished I knew how. Eventually I got tired of working with service personnel and the way they wanted to service my system (and the prices they charged and the oil and equipment they selected) and I finally said F__k it! I started doing my own work.

I learned something. I wasted time and money along the way, but I learned something, and now... I fix my systems when and how I want them fixed.

The OP left me with the impression he's a capable guy, and evidently he's willing to shoulder a challenge.

I say "Go for it".... and @351FUN, if you ever need someone to be a sounding board for you in this project, drop me a PM and I'll give you my contact info.

And @Eveready, I'm not disagreeing with you although it may seem that I am. "Pain in the @$$"... yup. "Fail"... I think OP can get it done. I did.

Now.... maybe I should buy a welder

 

[Eveready]

I sure wish I could weld. I was just looking at the nice job @Erik the Awful did welding his own exhaust system. D@mn that looks pretty...

350 Vortec Headers and exhaust

I want to say “maybe no” on this. Someone here tried it the other way (putting a Vortec Y-pipe on a TBI) and it was off at the header flange though you wouldn’t think that it would be. @DerekTheGreat was the guy that did that, maybe he could chime in. Here’s his thread, maybe it will help...

www.gmt400.com

I had never worked on an AC system until maybe 15yrs ago, but I had wished I knew how. Eventually I got tired of working with service personnel and the way they wanted to service my system (and the prices they charged and the oil and equipment they selected) and I finally said F__k it! I started doing my own work.

I learned something. I wasted time and money along the way, but I learned something, and now... I fix my systems when and how I want them fixed.

The OP left me with the impression he's a capable guy, and evidently he's willing to shoulder a challenge.

I say "Go for it".... and @351FUN, if you ever need someone to be a sounding board for you in this project, drop me a PM and I'll give you my contact info.

And @Eveready, I'm not disagreeing with you although it may seem that I am. "Pain in the @$$"... yup. "Fail"... I think OP can get it done. I did.

Now.... maybe I should buy a welder

I understand and I sure learned a lot with my attempt. The problem was that mine was just too far gone and everything needed replaciing. I do have the knowledge and equipment to maintain it fairly well now that it is working and I can easily handle minor charging issues etc. without paying to get it done. It was an experience for sure but having the AC working is worth whatever hassle you encounter. Good luck!

 

[351FUN]

I think I'll need some donor parts, since this and the compressor plug are toast.

You must be registered for see images attach

 

[east302]

You can probably get a new connector for it if you can’t find one at a salvage yard. The factory service manual may have the information for identifying the connector part number; they do for a 98, at least. There should be a sticky here for PDFs of the manuals.

@AK49BWL may know off the top of his head, I think he has a TBI as well.

​

 

[1998_K1500_Sub]

@351FUN, does your Blazer have the coolant crossover valve discussed here:

97 Tahoe 2-door: who makes the best quality replacement AC compressor?

Time to figure out what the root cause is. While you're at it, make sure the vacuum-operated coolant crossover valve, and its associated solenoid-actuated vacuum valve, are functional. I think they're present on the Tahoe; I know they're on the Suburban. Their proper operation will aid the...

www.gmt400.com

The 1998 service manual shows it used on the "Suburban / Utility" models, which would seem to include the Blazer (Utility). Of course, yours is a 1992 and may be different.