Attempted R-152a "Duster" A/C Conversion....some advice....

Bypassing it totally is better because you are sure no hot coolant goes inside.

The truck already has a coolant shut-off valve attached to one of the heater core pipes behind the dash.........circled in red is the lever that the temp. selector mechanism pulls via a cable.....



If your temp. selector mechanism is broken, it may not be pulling & pushing the heater coolant shut-off valve all the way through it's range of motion, thus leaving it opened some when you have the dash temp. selector turned all the way to the cold (blue) side. It is very common for the plastic housing on that selector mechanism to break, and therefore limit it's range of motion. To check it, just get down on the driver's side floor and look toward the passenger side and just above the gas pedal......you should see the area in the pic above and then locate the cable that connects to the shut-off lever......while watching the lever, turn the temp. selector knob on the dash.......does that cable pull & push the lever a fair amount? You can turn the selector knob all the way to the cold side, and then push or pull (can't remember which way, but you will know once you see it!) the lever near the gas pedal to see if it can be moved any more. If it can, then your temp. selector housing (behind the knob on the dash) is more than likely broken.

Don't let the "clicking" as you rotate the knob fool you! It will still "SOUND" as if it is doing it's job, but it won't push & pull the cable to the shut-off valve as it should!!

Here is one that I changed out of my 1991 B2600i.......looks good doesn't it?





Uh.....NO!



A close-up of the area where the lever is at by the gas pedal....

Here's a view of the heater core assembly as removed from a truck......with a little explaining added....



Somewhere I have a few pics of the valve itself, but can't find them right now....

You can run a test to establish whether any heat is being added from the heater core; if not, no need to bypass.

I'd say do this test after the sun goes down, after truck has been in a garage or in the shade for a few hours. Do not have the AC on. Measure the temperature from the vents after two minutes in the vent cycle, temperature knob rotated all the way to blue/cool. Then leave like that and drive the truck 15 minutes to get the engine fully warmed up (remember it's night, so no contribution from Tucson sun) and measure the temperature again at the vents. If the vent temperature rises significantly, then the heater core is contributing some heat.

One potential "bad" about bypassing the heater core is that then you couldn't turn the heat on full blast in summer and use as a second heat-shedding source in case of a radiator emergency. Like my trip to Pinetop one year in my B2200 before I replaced the original radiator with a 2-row....

Correct me if I'm wrong about this issue too, but with my experience doing heater core bypasses on other vehicles, isnt the heater core rusting out a serious possibility? Due to lack of running coolant thru it? I've had this happen on other cars in the past.

I think other than replacing the receiver dryer or expansion valve, biggest help I could give my interior temperatures at this juncture would be tinted windows. Shouldn't the tint drop interior temps by upwards of 20 degrees? And put far less of a load on the ac?

The heater core is brass with soldered tanks on it. It will not rust out. If you are worried about it just cap the tubes when you take the hoses off.

Yipes - I thought everyone here in Arizona already had tinted windows. I got mine tinted professionally soon after getting mine in 1994.

I also have tinted like two vehicles myself, actually tinted film. Gila is the largest manufacturer I believe. So if you clean the windows inside, and you're really careful, you can do the job yourself. I'll bet there are videos on YouTube too.

Yes, tint will help, so will parking in the shade (even if you need to walk further). That's what I do, and I park butt-end into the sun when I have to park without shade, the tint protects the dash, the seats, too.

Ok, so I ended up bypassing that de-icer switch and def helped with getting vent temps to their lower minimum levels. Been able to achieve mid to upper 30's when it's not 105 out...usually in mornings or evenings. Overall system seems to be ok, def would benefit from tint, as I can feel the improvement in temperatures as soon as I happen to be parked or drive under a shaded area like an overpass.

The only issue that seems to be happening is these compressor shut offs at the worst/hottest times. Seems like if ive been driving for more than 20 minutes or so during hottest time of day, after idling for more than 30 seconds or longer, the compressor will randomly shut off. I can hear the electric fan kick off too so I think it's something electrical doing it.

Only thing at this point I can fathom is perhaps somewhere along the line a high pressure cutoff switch was installed without my knowledge and somewhere not easily seen by me. I did remember from when I was doing the pressure testing and had the manifold gauges that the pressures did seem to go up significantly at idle. I assumed adding the electric fan on the condenser would help with this, and im sure it did, but what else could be triggering the compressor to shut off at these inopportune times?

Again, when it's working, its doing just fine now, but when compressor does shut off for those few seconds, it gets hot really fast. I should also mention that as soon as I start moving again faster than idle, it re-engages....again making me suspect some sort of pressure issue when its 105+ outside and ive been sitting too long.

Ideas? Suggestions? I supposed I could wire a toggle switch for the compressor.....or if anyone knows what a high pressure cut-off sensor would look like I could perhaps find it and at least know that's what's causing the issue.

Starting to wonder what I need to replace now....larger condenser? Add another e-fan? Perhaps expansion valve being clogged is causing this?

Just want the system to be working like it should and this doesnt seem normal.

Thanks again for any replies

Get tint. Welcome to Arizona summer.

No, my 1988 with R-12 and sock fan and fan clutch does not cut out at idle. ALL vehicles' AC performance will be less at idle: lower engine speeds and no ram air flow over the condenser. Sure, mine works better in shade as do all.

I would NOT bypass the circuit to the compressor with a dedicated bypass circuit. I think you'd really be playing with fire then; fire is hot too.

Hey Earl. Any idea where to score one of these? My broke the exact same way.
Thanks,
Steve