1984 k20 A/C Help.
 

Hey guys. I got this truck back in February and decided to try my hand at making it blow cold. It had absolutely zero pressure on the system and I even found some hand tight connections. I removed the compressor and hoses, opened up every connection. Flushed the evaporator and condenser with a can of flush in each. Blew out with compressed air. Replaced all O rings, accumulator, orifice tube, hoses, and a brand new 4 seasons compressor. Also swapped out the cycle switch for a 134a rated one. I pulled a vacuum in the system for over an hour. It held 29 inches for 24 hours. Charged it up with 3 12oz cans of Freon.
I’m currently sitting at 60 degrees coming out of the vent. My accumulator is sweating. Condensation is dripping from my truck. When i put it on max AC it blows for a second, I hear a door flip open and the air out of my vents sounds “harder” and it starts getting colder. When I turn it off I can hear a spring returning a door. My hot and cold lever seems to work well as well.

I was just wondering if anybody had any experience, thoughts, or input to try and get me closer to the 30 degree range.

Thanks,
Ryan

Re: 1984 k20 A/C Help.
 

Your symptoms point to:
1. Charge is not full, but enough for some cooling.
2. Heater blend door not closing fully

Re: 1984 k20 A/C Help.
 

What do you recommend for r12 to 134? My system is 48 oz of r12. I’ve read 80%, 90% and 95%

Re: 1984 k20 A/C Help.
 

IMO...You will NEVER get it to 30 degrees.......The lowest I have ever seen is 45

Re: 1984 k20 A/C Help.
 

Never gonna get 30 degreens, but I've got to get my 83's AC straightened out so I'm interested in what all you did.

Have a link to the compressor and hoses you used?

My system blows cold when charged, but I have a leak that appears to be in the compressor. It's an R4 and from what I've read they're almost not worth replacing they're so failure prone.

How many orings were there in the system? What kind of flush did you use?

I haven't worked on GM A/C before. My old Jeeps all used flanged fittings with no orings.

Re: 1984 k20 A/C Help.
 

I got everything at Oreilly’s. Prices were comparable to rock auto and I didn’t have to pay shipping.

New Murray R4 compressor
AC line (both hoses are made together on the compressor side)
Murray accumulator.

The old accumulator had a J tube built in that I had to buy a separate piece for, but from what I understand there are different styles.
R134A cycle switch.
Murray orifice tube
Pag150 oil

I would recommend replacing the high side schrader valve before you start, mine leaked after I got it charged the first time.

There’s an O ring on the top side of the accumulator, bottom side, J tube to low side hose. At the compressor, o ring for the high side at the compressor, o ring at the condensor, o ring out of the condensor, o ring at the orifice tube.

The flush I used was in an aerosol can, it’s nasty stuff. Spray it into the top of the evaporator and drain into a container at the bottom and push the test out with compressed air, same for condensor. That flushes and removes old oil.

I hope I’ve answered all of your questions adequately.

Re: 1984 k20 A/C Help.
 

I would bet your evaporator is dirty (Filthy!) pull your blower motor out & you should be able to reach it & clean it with a toothbrush & a garden hose.
If your psi is right, the discharge line is hot, the intermediate line is warm & that accumulator & suction line is cold then it has to be a dirty evaporator or the blend air door.
PS- you can check to see if the blend air door is the problem by putting your pinch off plyers onto the hot hose coming from the engine to stop the hot coolant from reaching the HVAC box. If it starts blowing colder then the door adjustment may be all or part of your problem.

Re: 1984 k20 A/C Help.
 

I installed a manual heater flow valve in the heater inlet hose keep it closed during the summer my vent temps went from 45 to 41 to 40 blend door is closed no need to circulate hot water thru the cab if not needed...........try it

Re: 1984 k20 A/C Help.
 

That's very helpful. Thank you for taking the time to respond.

Re: 1984 k20 A/C Help.
 

I believe ya bro! I did the same on my junky s10 I drive to work! But now the engine temp is a tad hotter!:waah:
But them 4.3s are tough, right?:lol:

Re: 1984 k20 A/C Help.
 

If the return from the heater runs to the radiator you can get away with bypassing the heater core directly to the return using a second valve... close the heater off and open the bypass valve. Since the heater isn't a radiator with the airflow bypassed you should gain back the summer engine cooling you're missing from completely shutting off that coolant flow.
Honestly if you're not overheating by blocking the coolant flow you should be able to install a bypass valve no matter where the return hose runs.

Re: 1984 k20 A/C Help.
 

I bought a cable operated heater control valve that I plan to have completely close off inlet flow to the heater core when the temp control is at full cold. My heater core returns to the "Cold"(passenger side) of the radiator, and it is my belief that this is what causes my 8.1 to slowly approach getting too hot when idling in the summer. I am hoping it will also help with the A/C vent temps. I am hoping I can connect the cable valve to the temperature blend door cable. the PN valve that I have bought to try out is Four Seaons 74828