HVAC issues - air isn't blowing from ANY location

[someotherguy]

Usually its the lack of airflow that leads to a frozen coil

You can see in that old pic of mine that sucker is almost completely obstructed with caked-on mud (dust from the air intake combined with the damp coils, it's a natural), and pine needles/leaf debris.

I took apart another when I was building my '94 3500HD project.. this core is from a '98 that had only around 100K or so on it, and the A/C worked seemingly fine. It was really dirty. Not as bad as the old pics from that '88 parts truck I posted earlier, but still surprisingly bad for the fact the A/C was still flowing air.

You must be registered for see images attach

It's worth noting you can do a *reasonable* job of cleaning this mess out without total disassembly of the air box, which requires pulling the dash and of course evacuating the A/C system of refrigerant. Big job. Pull the blower motor, *carefully* reach through with a small flexible vacuum hose to suck out loose debris. Then, cover your passenger carpet with trash bags or plastic sheeting and spray some evaporator core cleaning foam in there, then rinse it out thoroughly with water. You'll make a mess. It should get clean enough to hopefully not freeze up again, and should improve airflow noticeably.

Richard

 

[TexasAggie]

Right. I was thinking more along the lines of a way to literally see the evap and see if it was frozen. I'll test it this weekend though. I replaced the fan just a few thousand miles ago and cleaned out any debris that was in the housing (there wasn't much). I really don't want to have to pull the dash apart to get this issue figured out, but I can't imagine that the evap isn't clogged to some degree after 20 years. I'll give it a try as described above!!

 

[movietvet]

Right. I was thinking more along the lines of a way to literally see the evap and see if it was frozen. I'll test it this weekend though. I replaced the fan just a few thousand miles ago and cleaned out any debris that was in the housing (there wasn't much). I really don't want to have to pull the dash apart to get this issue figured out, but I can't imagine that the evap isn't clogged to some degree after 20 years. How big a job is it?

You are talking about dropping the HVAC unit out from under the dash and dismantling it to gain access. You will want to inspect everything while in there, not just the evaporator. Check blend doors and their movements, connections, heater core......etc.

 

[caw_86]

Right. I was thinking more along the lines of a way to literally see the evap and see if it was frozen. I'll test it this weekend though. I replaced the fan just a few thousand miles ago and cleaned out any debris that was in the housing (there wasn't much). I really don't want to have to pull the dash apart to get this issue figured out, but I can't imagine that the evap isn't clogged to some degree after 20 years. I'll give it a try as described above!!

if it were frozen you'd be able to stick you hand up there and feel it most likely.

evaporator shouldnt really clog, its just oil and gas in the system

 

[TexasAggie]

Where is the drain line located on these trucks?

 

[someotherguy]

Where is the drain line located on these trucks?

Plastic nipple with a rubber 90 elbow visible right next to the heater hose connections on the engine side of the firewall. Sometimes the elbow is missing.

Regarding literally seeing if the evap is frozen - you wouldn't see it without dismantling the hvac box. The suggestion I made will prove it is frozen. System working normally then airflow stops -> turn off A/C button -> airflow will return shortly and will be cold until it eventually warms back up after the ice melts. Trust me.. been there, done that, on several trucks, and suggested it to others that witnessed same results.

Pulling the dash out to get the hvac box out and then disassembled is a big job. I'd recommend cleaning it the "quick" way I mentioned earlier and see what your results are.

Richard

 

[TexasAggie]

Yep, the more I think about it, the more I'm convinced that you are right. The system was acting exactly as you described. Quick cleaning is on the agenda for this weekend. I did some more research and found a couple of other threads where folks used some kind of non-rinsing foam with pretty good results. Even if you do rinse, couldn't you take it fairly slow and let the water drain through the drain instead of getting it all inside the cab?

Evaporator Cleaner

 

[movietvet]

Yep, the more I think about it, the more I'm convinced that you are right. The system was acting exactly as you described. Quick cleaning is on the agenda for this weekend. I did some more research and found a couple of other threads where folks used some kind of non-rinsing foam with pretty good results. Even if you do rinse, couldn't you take it fairly slow and let the water drain through the drain instead of getting it all inside the cab?

Evaporator Cleaner

Isn't that foam for the times that mold builds up in the case and causes a smell?

 

[454cid]

Yep, the more I think about it, the more I'm convinced that you are right. The system was acting exactly as you described. Quick cleaning is on the agenda for this weekend. I did some more research and found a couple of other threads where folks used some kind of non-rinsing foam with pretty good results. Even if you do rinse, couldn't you take it fairly slow and let the water drain through the drain instead of getting it all inside the cab?

Evaporator Cleaner

Use a big sheet of plastic and you can direct the rinse water out the door. I dont have carpet or anything else on the floor so I didnt worry about it. I hosed it out from the heater core side, I think.

I dont think the box will hold enough to try to use the drain.

 

[jd33173]

@someotherguy gave you your answer on how to check if the evaporator is freezing over. When the problem starts, turn the a/c off and leave the air on and see if the flow gets back to normal, after the evaporator thaws. You can also attach gauges at the a/c and see where the pressures read and if you do that and post the pressures here, will need to know what the ambient temp is at that time of the pressures reading. BUT, if is clogged with lots of debris in front of it, that is a whole other can of worms.

If you do end up dropping the dash and going through the airbox, get some of the sticky backed foam insulation sold in rolls at the hw store so you can fix up the old stuff as it takes a beating over time. Once i got mine apart i was amazed any air had been able to flow through, it was pretty nasty.