Turn on a/c on = over heats....1999 Honda Accord LX
 

Last summer the car started to over heat out of no where. First I jumped the fans made sure they worked and replaced the relays and that did not work. I replaced the thermostat and that did not fix the problem. So then I replaced the temperature sensor and switch and that did not fix the problem. Then I replaced the water pump and that did not fix the problem. I replaced the radiator and that did not fix the problem. Couldnt think of anything else to replace so I tore the head off and replaced the head gasket and that did not work. Then one day I was driving and I blew a hole in the top radiator hose and replaced it. I also added an after market fan sensor that turns the fans on when it reaches a certain temperature. It never went passed 1/2 since that mod and worked fine all winter. Summer is just starting, so I am using the a/c and when I do the car goes 3/4. Can any Honda folks help me out here? I dont want to take it to the shop.

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

looks like u replaced most the stuff that could cause the problem. are you using a 50/50 water antifreeze mixture for your coolant? do you have enough coolant in the radiator? ide check for any coolant hose leaks

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

Are the fans turning the right direction?

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

Yes I am using 50/50 water and there is enough coolant in the radiator and there are no leaks. Where I park the car there are no spots on the ground. The fans are also running in the right direction. The only problem is when the a/c is turned on. Once a/c is turned off it cools down. My wife is pregnant and will be needing the a/c this summer.

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

this is a complete noob guess but is it possible the ac-alternator belt is too tight and putting a lot of stress on the engine?

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

that might be a good guess. I will check it out. Does anyone else think that is a valid reason? Can anybody else think of any other reason?

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

I dont see a mention of replacing the Radiator Cap?

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

No that is the only thing I have not replaced. I did not even think about replacing that. I will swap it with my other honda and if that doesnt do the trick I guess I wont go buy one.

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

Please post back with results, I am very interested...

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

I found this info here http://www.tegger.com/hondafaq/overheating/index.html




Bad radiator cap

The radiator cap does several things. It

* seals the system against the outside world (main seal function)
* keeps the system pressurized when needed, so as to raise the boiling point of the coolant
* allows excess pressure and coolant expansion to vent to the expansion reservoir (pressure seal function)
* allows coolant to return to the radiator when the engine cools down (return seal function)

As you may have gathered from the above section, the radiator cap has three seals, any of which may fail independently of the others:

1. The main seal is the one that seals the cap against the top of the filler neck. Just a rubber gasket that operates just like one on the lid of a pickle jar. Simple and reliable.
2. A failed pressure seal will allow the coolant to boil at a lower temperature, and coolant will be able to travel freely and foamily to the expansion reservoir. This will cause localized hot-spots inside the engine, which can lead to premature head warpage, and may hasten head gasket failure. It will also cause the rad coolant level to be low, just like a failed head gasket.
3. A failed return seal will prevent the coolant from returning to the radiator as the rad cools off, causing a vacuum that can collapse the radiator's hoses. This will prevent the coolant from circulating if the hoses don't re-expand as the engine warms up.

A bad rad cap can cause similar symptoms to a failed head gasket, so it's a cheap first step to try before bringing it in. If you replace the rad cap and you still have bubbles in the coolant (or foam in the reservoir), then suspect the head gasket.
If the engine starts to overheat at idle, or in heavy traffic, and the gauge goes down when you rev it, the coolant is probably low.

Moreover, a neglected cooling system can load up the cap with crud and corrosion, preventing proper coolant flow in and out through it. Peel the seals back with your fingernail to check for goop. If you find any, a blast with a garden hose and probing with a toothpick should clear most of it out.

But anyway, a new rad cap is less than $20. Make a habit to change it every 5 years, just in case. It's pretty important.

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

Did you have the head resurfaced when you replaced the head gasket? Have you done a leakdown test?

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

results?

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

sorry guys. I have been a little bit busy with college finals. I attend University of California, Santa Cruz. I have not noticed a difference when I switch radiator caps. I still want to do a leak down test though. I did not have enough funds to resurface the head when I replaced the head gasket.

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

I have the same problem with my 97 Accord. I changed the water pump while changing the timing belt and I had high hopes that the overheating would go away but no such luck. So far I changed the thermostat, water pump and ratiator cap. I'm currently deliberating on replacing the radiator and flashing the cooling system.
Please keep your findings here I'm very curious if you find the solution.

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

Air bubbles in the coolant? Did you bleed the system properly?

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

Well as the post said, I basically replaced the whole cooling system. I need to do a leak down test but I have not had the extra money to go pay a shop to do it. If I had a air compressor, I would buy the tools to do it. However, I do not have one, so I have to go pay a shop to do it. We went camping the other weekend and when it climbed the hill, it also started to over heat. This is a new symptom. The car before did not over heat going up hills.

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

When the car is warmed up did you check the radiator hoses ? Is one hot and the other cold or are they both warm ? Might want to test your thermostat:

Step 1
Follow your car's manual, or instructions on E-How, for removing the thermostat from your car.

Step 2
Check the thermostat for the rated temperature. It should be on the top.

Step 3
thermostat in cool water...closed

Rinse it well. Place in a pan full of water. Put the thermometer in with it. Start heating.

Step 4
As the temperature gets close to the rating you are looking for, watch the thermostat closely. If the lighting over the stove isn't the best, use a flashlight.

Step 5
It should start to open at the rated temperature, and be fully open as the heat increases. If it does not open, you may have found your problem, and can replace the thermostat with a new one.

Step 6
If the thermostat works correctly, let it sit in the pan to cool slowly as it would in the engine.

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

I replaced the thermostat with a new one. After it still over heated I did put it in hot water and it opened and closed correctly. However, both hoses are hot. Well actually the top one is way hot almost burning hot and the bottom one is very warm.

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

You need to make sure that when the A/C is turned on that the secondary fan is spinning. If not it will cause the car to overheat. Yes you can check the fans to see if they work but you need to physically see the second fan turn on.

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

Yes the secondary fan comes on. When the over heating issue first started, before replacing anything, turning on the a/c actually cooled down the car.

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

Were you able to bleed the system yet or change the cap ? not sure if anyone asked yet but do you have any coolant in your oil looks milky or white smoke coming out your exhaust ...

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

THERE IS YOUR PROBLEM! Resurface the head.

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

Damn, I have the same problem on my H22 too.

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

To be clear, when using the A/C do both the A/C condensor fan and the rad fan turn on?

Both the condensor and rad fans must be on anytime the A/C is on or overheating will occur. 94

Re: Turn on a/c on = over heats....1999 Honda Accord LX
 

Please tell me you used an OEM thermostat, dont use aftermarket on that, my personal experience.