AMS_

So I've failed smog magnificently, and have a thread here about it. About three times the HC or something, over CO a little, and over 3,000ppm NOx. I've read that a defective thermostat can cause emissions failure, and I've already replaced that. So I think the heating/cooling/radiator system might have something to do failing smog, but again it's just a hunch, and might just be another wild goose chase.

Now all settings, 1 2 3 4 work, but high does seem a bit weak, maybe it's not. I think air doesn't blow out of at least one air vent. And of course, doesn't get warm enough, just lukewarm. My other car 1 2 and 3 doesn't work, and it only works on high, and I've read that it's probably some resistor or some simple fix.

Car does not overheat, and warms up normally. Not overheating or overcooling. Both radiator fan and the other fan in front of the exhaust work fine.

I've replaced the thermostat, flushed the system and so much dirt came out, though maybe my drain pan was already dirty I don't remember for sure. I've sprayed a garden hose through both the inlet and outlet that goes to the heater core on the firewall. It's a 1992 Civic DX 1.5L 4-door D16B7. Still no luck. Tomorrow I'm going to add some radiator flush solution and hoping it's just a blocked passage, but that's a pure shot in the dark. It's running pure distilled for now because I might have to drain and fill a lot while diagnosing and replacing and repairing things for now.

I suspect that one hose that is connected to the radiator isn't getting coolant through it. When the car is warmed up, one large hose is pressurized and hot, while the other large hose, to the left and lower, right beneath the radiator, seems flaccid and cold. I'll check that hose again tomorrow but what does someone think it might be?

I'm also probably going to throw another part at it, a universal vacuum check valve, because it's $4. And if I need a more expensive part, it's a trip to the junkyard for me.

What kind of tests can I do or other things I should check for? I will also properly bleed the system tomorrow. So many problems can result from air in the cooling system I'm just finding out, I never knew. Strange.

strategy400

You should run 50/50 antifreeze mix, just drain to a clean container and pour it back in if you need to.
I'm tempted to say your radiator is clogged but as its not overheating we will not go there.
Is the heater coolant valve by the firewall opening properly? See that the valve operates when adjustment is made from the inside console (you'll need an assistant). If it doesn't move there is a pushrod under the dash just to the right of the radio that sometimes gets knocked loose by a passenger's foot. Make sure its connected. You can see it easily if you look under there with a mirror. Mine came loose once and I could see my breath in the car for a week before I discovered this.
I'd say if the car warms up normally you should look elsewhere for your smog failure (cat maybe?)
If you are considering replacing any coolant hoses get them from the Honda dealer. They are surprisingly cheaper and better than your local autoparts.
If you try to get the hoses off the heater core be careful the metal pipes coming out of the firewall are thin as tin foil and will bend/collapse/crack/tear if you look at them sideways. I always cut the hoses off and replace if they are stubborn. If you do accidentally crush/twist them with pliers you can round them out again by working them from the inside with a small deep socket. I bought some screwdriver like tools with hooks to work stubborn stuck hoses loose with.