Automotive Air Conditioning Information Forum

Background. 90 K5 converted to r143. New condenser parallel flow, new evaporator, new accumulator, tried white and red orffice tubes, both new. Sanden compressor not new but maybe only used a year or two before sitting on a shelf for a year or two. Low pressure switch not changed, no high pressure switch.

system is supposed to hold 44 to 48oz r12, so started with 36oz r143. Drained oil from compressor, flushed system, added 6oz oil, that is what the Sanden calls for.

Can only get it down to about 70 degrees. Switched to red orffice tube and could only get it down to about 73 degrees. Yes, it got worse, not better. Granted, it is Texas and 97 degrees out when it was done.

What am i missing? Held vacuum fine at 29lbs. both times. Flushed out system first time, just added about 1oz of oil second time because lost that evacuating the system but did not flush. First replaced white orffice tube when pulled out had some minor metal shavings and the tube had discolored a bit meaning some degradation of the oil? Original tube was almost black but no telling how long it had been in there before i started swapping parts and it was in there with another compressor.

No leaks. But can not get the evaporator car side temp below 70 degrees. Compressor seems to be working. At idle with 36oz of 134a the low is just under 60 and the high is close to 300. But spraying water on it drops the low to under 50 and the high under 250 so thinking that is just the 97 degrees ambient temp.

I thought about scrapping the factory evaporator and installing the under dash vintage air system, but i do not see how that is going to help other than giving my defrost and feet air back. Currently have the factory system forced to all dash. Vacuum actuators are bad and can not find parts to replace. Really do not want to spend 1k for the vents when all i really want is the AC. But i will if someone can convince me the after market evaporator will solve my temp problem.

Any help is appreciated. I am at a loss other than throwing another 300 bucks at it for another compressor and more r134. It is the only part i have not replaced but it acts like it is working and does not seem to be having any issues, noises, low pressure on the high side or any other problem.

There are others here waay better with conversions.
But I will introduce a few comments to get you started.

" But spraying water on it drops the low to under 50 and the high under 250 so thinking that is just the 97 degrees ambient temp."
No, that means your condenser is not doing its job.
Condenser should be mounted as close to the rad as possible, like no more than 1/2". There should be air dams all around to make sure the air goes thru the cond and not around it.
Your clutch fan is likely weak. For AC purposes, they only last 2-3 years. The fan clutch must be in top notch shape, else it will not pull enough air. This is a performance range where the engine will not overheat, but the AC will be horrible. On this board it is advised to replace every 2-3 yrs.
I do not like the sounds of the colors and metal bits on the OT
What kind of oil did you use?
How long did you pull a vacuum?
Is your vac pump run by an electric motor?
Not sure why you would choose a used unknown comp when all else is new, especially with all that work.
Have you ever charged a system before? It is easy to introduce air if you are not careful. Some skill is required, not meaning to insult you, just stating facts, and I wasn't there to watch you

We need pressures not at idle, but under these conditions: (full load)
1500-1800 RPM
max fan
max cool
recirc
doors open
center vent temp taken with a dial probe such as found on the internet.
such as https://www.amazon.com/UEi-Test-Instrum ... 129&sr=8-2
IR temp guns are not accurate for this
report back.

JohnHere and others will be along soon to jump in.
If you are willing to work with the experts here, they can get you better center temps. These guys are top notch

IS the inlet and outlet on the evap tubes the same temp?

Ok, at 2k rpm outside temp 93 degrees.
high side - just under 300
low side - just under 40

evaporator temp taken at the tubes going into and out of evaporator.
inlet temp - 75
outlet temp - 64

All those new parts.

As cars get older, and 3rd party aftermarket parts are the only choice - questions like this get tricky.

1990 may have been a PF core to start with, and about 28" x 16". Plenty of condenser. IF it is all working. Several of us here have found offshore parts with manufacturing issues leaving blocked tubes.

New evaporator. Same issues are a possibility. We had a poster here last year with an expensive custom built evaporator that we presumed to be a good part. After a lot of tail chasing it turned out to have blocked passages.

Having said that, let's work through all of the basic stuff first, presuming your heat exchangers are ok.

Charge level. The system should hold the same quantity of 134a or R12. The 80% rumor goes back to conversions where the plan was to leave the old oil in place and add ester oil as well. The old oil took up volume in the system, and so the charge was reduced.

With the full 44 ounces of 134a in the system, evaluate the performance with the cabin fan on highest speed and both doors open. Engine rpm above 1500, and hold for 90 seconds to stabilize the system. Take your high side, low side and vent temp readings while the engine is above 1500 rpm.

As for the evaporator box being a mess, as long as all of the air goes through the evaporator, and in to the cabin - all is well. If it is somehow reheating the air with the heater core, that can be a problem.

I doubt an aftermarket evaporator only assembly would be an improvement. If you truly don't care about heat or defrost your OEM parts could be made to work.

Let's start with a full charge and a full load test, and go from there

ok, i will add another 12 oz and get back to you.

A couple of questions: If everything is new except the compressor, what did you flush? And if you flushed the Sanden compressor, did you do so only with PAG oil, or did you solvent-flush it?

Just reread the Original Post.

SANDEN compressor?

OEM was an R4 compressor. Is this an engine swap truck?

rosco11 wrote: ↑Mon Jun 27, 2022 12:29 pm system is supposed to hold 44 to 48oz r12, so started with 36oz r143. Drained oil from compressor, flushed system, added 6oz oil, that is what the Sanden calls for.

By way of comparison, and according to the specs that I have, the 1990 and 1991 C and K series Blazers (with the R4 compressor) take 44 ounces net weight of R-12 and 8.0 fluid ounces of Mineral Oil.

it is a LS swap with a sanden compressor. Specs for the compressor say 6oz of PAG. The C series and the K series actually have different AC systems in 1990-91. The K5s still used the same carry over system from the 85s. While the C went with a newer system along with the surburbans. For instance, the K in 1990 still have the evaporator in the engine compartment where the Cs and suburbans moved under the dash inside of the vehicle. The info i have says 44 to 48oz of R12.

The only part of the system not original is the compressor, modified hoses and the new parallel flow condenser. Everything else is 1990 K5. For now. Trying to make it simple so next owner does not have a WTF is this moment when buying parts.

The compressor that came with it, along with the engine and transmission is at the scrap metal place. And 8 bucks was a bargain IMO.