Air con blows cold only on freeway.

[BennyM]

Last summer, I put a new Aux fan in my car and had my mechanic recharge the AC. Everything checked out. Pressure good, no leaks. But, the mechanic told me the air coming though the vents never got as cold as it should. Sure enough, it only gets slightly cool when running below freeway speeds (about 50mph). If I take an extended freeway trip, it's gets much colder, more like how it did when I first bought the car.

He suggested the heater core area might be clogged and wanted to rip into the dash to find the problem. I said "no." Another mechanic friend suggested that the radiator might be really dirty/clogged, but wouldn't the engine be overheating if that were the case? Any other suggestions as to what I should look for. Or how best to tell if that mysterious area between the blower motor, the pollen filter, and the heater core is the culprit?

thanks in advance!

[bsell]

Last summer, I put a new Aux fan in my car and had my mechanic recharge the AC. Everything checked out. Pressure good, no leaks. But, the mechanic told me the air coming though the vents never got as cold as it should. Sure enough, it only gets slightly cool when running below freeway speeds (about 50mph). If I take an extended freeway trip, it's gets much colder, more like how it did when I first bought the car.

He suggested the heater core area might be clogged and wanted to rip into the dash to find the problem. I said "no." Another mechanic friend suggested that the radiator might be really dirty/clogged, but wouldn't the engine be overheating if that were the case? Any other suggestions as to what I should look for. Or how best to tell if that mysterious area between the blower motor, the pollen filter, and the heater core is the culprit?

thanks in advance!

Pressures were good and no leaks but the system needed recharging?? I wonder if the freon dissapeared just like last time?;)

Your symptoms sound like a lack of capacity problem or hot water getting into the air box through the heater system.

Things that can stop up the flow of freon are your receiver/drier (clogged filter), junk in the expansion valve/orifice tube (don't know which one you have) from a receiver/drier falling apart, or a weak compressor that doesn't have the flow no mo'.

Do you have the auto climate jobbie or is a manual rig? Either way, check that the heater valves are not stuck open allowing hot water into the heater core (and the air box) when you want cold air. If the heater valves are behaving, then maybe your air temp doors in the air box are not behaving and allowing warmish air to mix with your cold air.

I agree that if you had a clogged radiator, you would know that by now.

Brian

[Tiger]

All you need is a good set of manifold to find out what is the problem... like for example... on R134a system... with AC compressor running and aux fan running,.. low pressure is about 25 to 30 PSI...and high side should be around 240 PSI...

If the High side pressure is above 300, then your aux fan is not running...

If the high side pressure is below 200, then your expansion valve is bad.

You need to check if your heater monovalve is working too... because the heat it put out... will overcome the AC that it will never cool down the car.

[mikell]

Good advice - sounds like a heater valve could be the culprit - and, be sure that the heat thumbwheel in the center of the dash vents is on full cold.

[BennyM]

My aux fan does run when necessary. The expansion valve is the newest component and has lived a pretty low key life as I hardly ran the AC for a couple years. I really don't think it's bad.

Also, if the heater were interfering, wouldn't that mean that the system would never blow cold?....even on the freeway where it presently still gets cold?

What's the easiest way to check the heater valve?

Thanks.

[BennyM]

Thanks for your insight. I have a few thoughts for you in response.

I should have given you more back story. A few years ago, the aux fan seized, causing the AC system to over-pressurize and blow the expansion valve. All the refrigerant (R-134) leaked out then. I had the valve replaced, and didn't get it fully recharged until I could put an aux fan in.

Interesting...I never thought of the heater system interfering. How does this all work with the higher speed correlating with colder temp?

I believe all of these primary AC components are 5 years old at most. For the sake of my wallet and experience level, I'm going to assume that the receiver/dryer, compressor, and expansion valve are all still good and I'm going to look for causes elsewhere.

I have the manual rig and yes I have the thumb wheel at cold. I'm up for checking the heater valves and temp doors. I wouldn't be surprised if it was a stuck door. Any suggestions on checking these would be much appreciated. I assume I'd have to take apart most of the upper center console?

[bsell]

My aux fan does run when necessary. The expansion valve is the newest component and has lived a pretty low key life as I hardly ran the AC for a couple years. I really don't think it's bad.

Also, if the heater were interfering, wouldn't that mean that the system would never blow cold?....even on the freeway where it presently still gets cold?

What's the easiest way to check the heater valve?

Thanks.

Please define 'cold' for us. As in get an instant read or 'a/c' temp gauge to fit in the center vent. Compare temps at idle and at highway speeds. You should be getting around a 40 degree F drop over ambient. You might be surprised how warm 'cold' can be when using your skin as a temp gauge. ;)

With the car warming up, take a feel of the heater hoses at the valve and going into the firewall. If hot water is making it past the valve and into the firewall with everything set to full cold, you have leaky valves.

Brian

[bsell]

Thanks for your insight. I have a few thoughts for you in response.

I should have given you more back story. A few years ago, the aux fan seized, causing the AC system to over-pressurize and blow the expansion valve. All the refrigerant (R-134) leaked out then. I had the valve replaced, and didn't get it fully recharged until I could put an aux fan in.

Interesting...I never thought of the heater system interfering. How does this all work with the higher speed correlating with colder temp?

I believe all of these primary AC components are 5 years old at most. For the sake of my wallet and experience level, I'm going to assume that the receiver/dryer, compressor, and expansion valve are all still good and I'm going to look for causes elsewhere.

I have the manual rig and yes I have the thumb wheel at cold. I'm up for checking the heater valves and temp doors. I wouldn't be surprised if it was a stuck door. Any suggestions on checking these would be much appreciated. I assume I'd have to take apart most of the upper center console?

With the system overpressure event now known, I wonder the condition of your compressor and clutch. Is it possible your clutch got cooked turning the compressor hard enough to blow up your expansion valve and now it slips enough to under-drive your compressor at low engine speeds? This is kind of a stretch as you would figure the weak/burned clutch couldn't hang at high engine speeds...

Or is the compressor worn and weak from the years and the overpressure event, causing poor low speed performance?

It would be interesting to see the gauges during stationary and highway operations to see what is going on. I assume you have a clear sight glass, as in plenty of freon to get a steady supply of liquified freon at the expansion valve?

If you can do the temp gauge thing I wrote about above and let us know the results. The temp gauge shouldn't cost too much (<$20 for sure).

Brian

[bill g]

Make sure you have the aux fan wired up correctly and that it is not spinning backwards and blowing in the wrong direction.

Bill G

[ThoreauHD]

The heater valve does get stuck open. Also the aux fan resister may need a replacement, but I'd bet on the heater valve.

[DanDombrowski]

All of the other advice is good, but I think the answer is pretty obvious to me.

If you're running cold on the freeway (as in, its working properly), but not at idle, its either a problem with airflow across the condenser, or the compressor isn't working well at lower RPMs. Checking the high side pressure will sort out the second scenario.

Now, you say you had the aux fan replaced, but if the condenser is clogged with dirt/debris, it won't matter much. Take a look at how much dirt you see in there, and maybe try to hose it out from the back.

Here's a quick test you can do before you buy any new equipment - at idle, turn on the AC and spray a garden hose on the condenser. If the AC turns icy, you have an airflow problem. If it stays the same, you have a pressure problem. Good luck with it!

[BennyM]

Hey Brian,
The mechanic actually measured the temp as you described when he recharged the system. He told me it was supposed to be around 40F, but was inexplicably higher.

After driving the car around the city, I checked the heater valve hoses. They all seemed warm from the ambient temp under the hood, but not hot as I would expect if the valve were interfering.

[Barney Paull-Edwards]

Pollen Filter!!!!!!!!!

[bsell]

Hey Brian,
The mechanic actually measured the temp as you described when he recharged the system. He told me it was supposed to be around 40F, but was inexplicably higher.

After driving the car around the city, I checked the heater valve hoses. They all seemed warm from the ambient temp under the hood, but not hot as I would expect if the valve were interfering.

I like Dan's 'shade tree' idea of spraying water on the condenser to see if your problem is a heat-removing problem.

Yet, you may have something as simple as an air-flow problem caused by a dirty cabin filter. The extra air pressure at the cowl could help blow more air through a clogged cabin filter, making the inside of your car cooler.

I take it your pressures were good but the temp at the vents was warmer than it should be? I would figure inadequate heat-removal would make the high side pressures high while a clogged filter would make the low side lower. Any idea what the pressures were?

Brian

[Ross]

If there is a blockage in the heater core/evaporator area the airflow will be diminished as well. I vote for a weak compressor or a very dirty condensor which the mechanic should have checked while replacing the aux. fan.

[BennyM]

Right, except I replaced the exhaust fan. So, it's my fault for not checking.

[BennyM]

I replaced that a couple years ago. I will check it again soon.

[BennyM]

Thanks Dan. I did the test twice and experienced no change in temp. Guess it's a pressure problem. I should probably clean out the condenser anyway, since that's probably never been done, but from what you're all saying, I'll probably have to replace the compressor, huh? Boo that.

[Milkboot]

Would this apply to most cars? Been borrowing moms Jeep while i work out my own problems with my lil e34 and it sounds like she has the same basic problem


Been jumping curbs at the corner just to keep on moving to get the cool air going!

[Bin_jammin]

I'd gamble on an issue with the aux fan, either the fan motor or the resistor. At idle it's not functioning properly and the high pressure switch is turning the system off. Cruising on the highway will aid the operation of the aux fan, making you cold.

[bsell]

Would this apply to most cars? Been borrowing moms Jeep while i work out my own problems with my lil e34 and it sounds like she has the same basic problem


Been jumping curbs at the corner just to keep on moving to get the cool air going!

Whachyo talkn' bout? The water on the condensor deal or having a weak compressor/low freon charge?

Some a/c systems run the aux. fan after a certain pressure is reached on the high side so if you don't have enough freon in the system, fan no workie. Of course, if you fool the system into thinking it has enough freon (jump the connection at the switch connector) then the aux. fan should run.

The best way to figure a/c systems out is to use a proper set of gauges, a known good thermometer, and the sight glass if equipped.

Brian

[DanDombrowski]

In theory, yes, without the aux fan you will have poor cooling at low speeds and adequate cooling at high speeds. However, in this case, we tested two things at once by running a garden hose over the condenser - blockage and airflow.

Because running water will extract heat far better than any moving air, I told him to run the garden hose over the condenser and see if anything changed. With the condenser presumably much cooler than normal, the AC still did not function properly, ruling out both debris blockage and a bad aux fan as the main culprit.

[Bin_jammin]

I've figured it out. Just roll down your windows.

[xspeedy]

This could be you :p

http://gizmodo.com/assets/images/gallery/4/2007/08/medium_1069838461_200e833710_o.jpg