Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Intermittent Honda Accord air conditioning - and engine overheating

My 2002 6 cylinder Accord has AC trouble. I noticed it a little last year, this year it’s serious.

When driving at low speeds, or stopped at a light, the AC often stops blowing cold air. In fact, the air becomes almost warm and feels a bit moist. I thought it might just be the compressor “getting a bit lazy” in its old age or perhaps a belt slipping.

But last week, while crawling home in Boston traffic, I noticed that when the cool air stopped the engine temperature gauge climbed fast, and high. Now that I’m looking for this I’ve seen it a couple times since.

Speeding up the engine (either putting it in neutral and giving it gas or by accelerating when the traffic starts moving again) starts the cooling again after a few seconds and the temp gauge drops.

Any ideas?

I don’t think your problem is with the AC. Honda controls the AC through the computer. When the engine temperature starts to rise, the computer is probably shutting down the AC to protect the engine.

Open the hood and see if both fans are running when the AC is on. If one is not, then you need to replace it.

There are two things to check.

First, make sure the cooling system is full. Check the radiator itself, not just the overflow reservoir.

Second, make sure the radiator cooling fans are working. The symptoms you describe are often caused by non-working cooling fans. If you start the engine and let it idle, the temperature gauge should come up to normal, and as it starts to climb the fans should come on to cool the radiator.

The cooling fans should both come on when you turn on the AC, too. The fans remove heat from both the radiator and the AC condenser, which is mounted directly in front of the radiator.

If the fans aren’t working correctly the engine will overheat at low speeds and the AC won’t cool correctly.

Thank you both for your inputs. The cooling fans are both working, they turn on as soon as the AC does, I’m going to let the car become good and hot then try to create the non-cooling problem and see if perhaps one of them stops working.

The cooling system is full, both the radiator and the overflow reservoir.

One thing I did notice just now - when the AC kicks in I can hear “a funny noise” from the serpentine belt area. As is often the case, such noises are hard to describe. This one sounds a little like grinding.

I wasn’t going to suggest this earlier because you car isn’t that old, but you may have a waterpump problem and this can get very serious very quickly. I’m not sure about the V6, but the waterpumps on the 4 cylinder engines are driven by the timing belt.

If the pump starts to leak or seizes up, it can cause the belt to break, and since it is an interference engine, that will result in more than a few bent valves. That will not be cheap to fix.

Yes, I once had a timing belt break on an Accord - a darned pricey repair!

You said I might have a water pump problem - how would that be evident? The car never overheats (other then recently due to this air conditioning thing). How can I tell if the pump is bad?

Is there any way to tell if the “funny noise” it the water pump? This car has 120,000 on it, a little overdue for the belt replacement. Should I just get the timing belt done and have the pump done at the same time anyway?

You should get the belt replaced immediately if you are at 120,000 miles and it has not been done. On Hondas one should always replace the water pump at the same time since it is driven by the timing belt and it is cheap to replace while you are in there but darned expensive to replace if you have to do it 25,000 miles after a timing belt.

I’d heard that same advice about doing the pump elsewhere, I definitely will do them both. I’m going to set an appointment for next Friday if I can.

However, I remain perplexed as to how a water pump problem can cause the air conditioning to stop blowing cold air when at Idle and the engine temp to skyrocket.

I don’t know if the tbelt and pump are your issue but they might be. if the water pump is dying then you will get less engine cooling. When things get hot the computer will shut off the A/C cooling to try to cool the engine down more. I am not convinced that this is your problem however if you do not replace the tbelt and water pump I am convinced that you will have many more problems.

Well, I’ll get those done next week and hope the water pump is somehow related.

The signal to the compressor clutch comes from the computer. Just turning on the AC switch does not automatically turn on the compressor. There are a bunch of signals the computer uses to determine when the compressor should run.

I don’t have the wiring diagram for your particular car, I do for my 97 Accord. Unfortunately I cannot find the diagram for the AC section of the computer other than the the wire to the AC compressor clutch comes from the computer. I do remember seeing it for out 93 Civic and it had about 10 signals that it processed before allowing the compressor to come on. I don’t remember what all of them were and don’t remember if engine temp was one of them, but I suspect that it was.

Since running the AC causes the heat load on an engine to go up, your Acura may be shutting off the compressor when it detects a higher engine coolant temperature in order to protect itself.

BTW, this next piece of info is not really recommended anymore for safety reasons, so be careful. When the engine is cool enough to rest your bare hand on the radiator cap, remove it. Then run the engine until it gets hot. You should be able to see some circulation of coolant in the upper tank at idle. I don’t know it this will help you because you would have had to see this when the pump was known to be working good to compare with now.

I have to say that I would be a little disappointed if the pump is bad. I have had waterpumps go 2-300k miles for me with out a hitch. But since you need the timing belt, definitely do the waterpump, it is recommended. You have been changing the coolant every 4-5 years haven’t you? You have not ever used a chemical flush in your coolant system have you?

What perplexes me is that the air goes from cool to warm/moist AND THEN the engine temp gauge climbs fast. In other words, it’s not the engine temp that is causing the computer to shut down the AC compressor. The cooling stops AND THEN the engine temp rises.

I do have the official Honda service manual for the car so I’ll check the wiring diagram to see what feeds the computer to tell it when to turn the compressor on/off, what overrides it, etc.

As for coolant flow in the radiator, if it were not flowing well at low RPM then I assume the engine would overheat, or at least show a considerable rise in temperature - even if the AC were not on. But, as mentioned above, the cooling stops AND THEN the engine temp rises. When I rev the engine or disengage the compressor the temp drops to normal fairly quickly.

I don’t have an answer for you on that. What I do know is that a worn out water pump can cause an engine to overheat at idle and revving the engine causes it to cool down.

The only other connection would be if the V6 water pump is driven by the serpentine belt instead of the timing belt. I am familiar with the Honda 4 cylinder engines, but not the V6. If the water pump is driven by the serpentine belt, then the belt could loose traction and allow the water pump and the compressor to slip.

One more very remote possibility is that the idle is too low. If it dropped to 500 rpm, it might do the things its doing.

This morning I picked up the car after having had the timing belt, serpentine, water pump, and thermostat replaced (the thermostat was a “just in case” item that didn’t cost much since they had the car apart anyway). They also found the AC system was down about half-a-pound out of, so they tell me, a prescribed level of about 1.5 pounds.

I’ll report back in a few days as to my success - or lack thereof.

It’s been two round-trip commutes, 42 miles each way, on the Mass Turnpike with no sign of overheating. I believe I can declare victory. I changed out both the water pump and thermostat so I’ll never know for sure which was the winner - but there was a winner.

Thanks to all for the advice.

A solid week of commuting - I declare victory! Thanks to Keith and Bloody-knuckles for your assistance.