Wondering if anyone can offer help or ideas on what might cause an intermittent problem with the a/c and heater.

Problem started in the winter when the heater would suddenly cut out, but would eventually start again.

It has continued in the summer now with the a/c suddenly turning off (and eventually starting again).

When they are running, both are working fine. Hot air from heater when running seemed a little hotter than normal, after it ran for a while. A/C air temp seems about what it has been.

Trying to isolate what is going on operationally with the car at the time this odd on-off cycling occurs has been hard.

I thought it might be related to the heating control *****. Then, it seems it might be related to whether the car was in stop-and-go at lights versus running smoothly at speed for a while.

All I can say is that it does seem to be more of a problem during stop-and-go, for both heater and a/c, than for running, but they both have cut out intermittently on the highway too, so that might just be coincidence.



'04 Honda Civic, no work ever done on the HVAC on this car

 

Do you mean that the fan inside the car stops running, so little or no air comes out of the vents?

On models 1998 (I think, it may be 1996) and later, there is a component called the power transistor, which controls the fan, and they commonly go bad.

 

Thanks for reply. No, the blower is good/strong still. It runs strong, but the air temp changes.

New information: I noticed just today that the car temp sensor is going through what I consider wild swings, from "normal" while at 45-50 mph to "hot" when idling at a light (and just after, during acceleration). So, it may be that the car is overheating for some reason and causing the heating-a/c unit to cut off.

The overheating that occurred today was at one point severe (needle all the way to "H"!). This may be a new problem or it has just gotten worse. *sigh*

I'm going to look for a troubleshooting guide on overheating. Anyone who has any recommendations, I'd be grateful for the saved time.

I know the radiator fans are operable, because I had the car key just on 'power on' and they ran. However, I didn't hear them running when the engine was running; I observed them not click on during idle when the car overheats; and I wasn't able to get them to turn on a second time with the car key just in 'power on'.

I put some coolant in the reservoir while I was stopped to let the car cool. It needed some, but it was hardly desperately low or dry.

grrrr...wasn't expecting this!

 

recap: Air bled the cooling system and this seems to have helped so far.

Monitoring for further problems.

 

yeah i was going to say air bleed or water pump or even the radiator cap could cause this issue.

 

Okay, so no more engine overheat but the problem with the a/c reappeared yesterday.

It's hard to figure out what set of conditions is causing the a/c to cut out.

It was a hot day outside. That seems to be a co-factor.

Going to have to research a/c systems, which I don't know much about. Thought it might be low refrigerant, but that doesn't dovetail with the problem with the heater IF the two are linked.

Odds on guess now seems to be some kind of thermometer problem or some mechanical problem that is making it hard to the "system" to "start and stop" or whatever...

Is it easy to check the refrigerant levels/pressure/whatever yourself on this car, i.e. basic preliminary diagnostics?

 

The first step toward a preliminary diagnosis is to drive until it stops making cold air, then pull over (leaving engine and A/C on) and check under the hood.

1. Is the compressor engaged? (clutch plate spinning, not just the pulley).
2. Are the radiator / condenser fans running?
3. Is the line from the evaporator to the compressor cold? This is the line from the firewall that goes over the top of the engine and connects to the compressor.

If it gets cold once, you have enough refrigerant. The problem is something else.

 

maybe a clog in the system if you haven't been using the proper coolant then corrosion may have occurred in the system.