Last post on Oct 07, 2013 at 12:52 PM
You are in the Mazda CX-7
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Mazda CX-7, SUV
#171 of 294 CX7 - blows hot air & inadequate cold air - faulty body design
Jun 26, 2010 (11:49 am)
Have significant issues with hot air blowing always with the AC turned off. Plus the AC has trouble to cool on hot days. These symptoms are parroted by a number of the previous posts. Seems the problem is prevalent in every CX-7 with automatic climate control and dealers tell you to just live with it by turning on the AC.
After considerable diagnosis and taking apart the under-hood shroud assembly, it turns out the HVAC climate control system works pretty much correctly. My CX-7 only minor fault is the blend door, bottom left regulator arm as you look through the glove box opening, does not fully shut so there is slight heat from air leaking through the heater core. Most of the hot air however comes from the engine cowl and windshield shroud assemble. The primary airflow into the cabin from the outside setting actually comes indirectly from the engine compartment and not outside. This happens because there is a metal bottom channel under the leading edge of the windshield covered by a plastic shroud assembly the width of the dash from which the heater draws air. The channel is not effectively sealed and the backside of the under-hood firewall seal is open at the both ends of the shroud. There are some perforations along the window side of plastic shroud but they are mostly not effective.
If you doubt, just put a thermocouple type furnace or air conditioner thermometer into the crack above the cabin air filter and watch how the temperature changes as the car operates. You will observe the hot air does not in fact come from the heater assembly but instead from the heater blower air inlet up under the windshield.
When the CX-7 is moving outside air is drawn into the engine compartment through the radiator being accordingly heated. There is a large plastic cover on the underside of the compartment so not much air enters there. Compartment air is accordingly rammed through the openings at the under-hood back corners directly into the windshield channel. The channel is metal located above the turbo, exhaust pipes and inter-cooler so it gets very hot the longer the engine runs. So the very hot channel passes mostly engine compartment air already hot into the cabin heater inlet. And it does so always which means the AC compressor and system must compensate for the additional inlet heat.
Collateral problems are the climate control system assumes the inlet temperature to be the ambient temperature as shown on the dash gauge. Assume the system would malfunction so not necessarily blow enough cool air. There is also the problem of the AC system being over worked which probably leads to premature compressor failure. There is also the issue of health risk from cabin occupants always breathing air from the engine compartment. On the up side, the air re-circulation function works independently to close off the outside air inlet. Just click the switch on and you block the under-hood hot air from entering the cabin. Only catch is you then have no ventilation and must open the windows.
Short story, the climate control system does not in fact draw air from the outside when set to do so. Instead it draws air mostly from the hot engine compartment whereby the air conditioner must be always on to compensate.
A disappointing proposition as it looks there is no way to correct the problem. And there looks to be dozens of CX7 owners who are bothered by the issue. Unless the engineers at Mazda to provide a modified plastic shroud assembly with a sealed cowl and outside grate perforations to prevent the air from the windshield channel and essentially engine compartment air from entering the cabin. Such a modification is surely possible and would not be terribly costly to install en mass as every CX7 would need one.
Sorry, there is no fix and nothing actually wrong with the HVAC. The fellow at 166 had the story correct except the cause is complicated and issue more substantial than most of us would expect.
#172 of 294 Re: CX7 - blows hot air & inadequate cold air - faulty body design [e_buster]
Jun 26, 2010 (12:53 pm)
The extensive analysis and explanation by e buster is wonderful! This may be a bit of a stretch, but does it look like it might be possible for the owner to make some or all of the suggested mods to at least improve on things?
#173 of 294 CX7 - blows hot air & inadequate cold air - ADDENDUM
Jun 26, 2010 (9:34 pm)
Today the outside temperature here was 75F both on the CX7 ambient readout and according to the weather report. When my CX7 was started the HVAC inlet air temperature, measured immediately above the cabin air filter, showed as 75F and stayed there for at least 10 minutes. After an hour of city driving with a few stops between the HVAC inlet air registered 105F about. Under-hood temperatures are upwards of 135F at the firewall bezel just below the windshield behind the inter-cooler. The lowest possible temperature my CX7 air conditioner could manage was eventually 65F. Which is just not enough to cool the vehicle much below 75F in the sunshine with the windows closed.
The AC unit was therefore working to cool incoming air at 105F instead of outside air at 75F. Which means the compressor has to run constantly just to keep up with pretty modest outside temperatures. With the re-circulation turned on, so no external air is used and inside already cool air is cooled again, the AC unit can eventually cool air to 35F but then only at lower outside temperatures. Assuming the under-hood air temperature would always be greater than the outside temperature, it would be a whole lot better if the AC was fed with outside air directly. It seems obvious the AC unit would then have cooling capacity to handle outside temperatures equal to the 105F it currently gets at 75F. As you can see, the hotter the air you put into the system the higher the temperature of the cooled air output.
Unfortunately, Mazda vehicles are pretty much the same design with a plastic covered metal cowl structure under the windshield with inadequate firewall seals and, with very hot engines jammed so tightly in under-hood compartments, the design does not work. The result is the HVAC units work inordinately hard to compensate for often hot inlet air temperatures. Which means vehicles have inadequate cooling much of the time and hot air when the AC is turned off.
#174 of 294 Re: CX7 - blows hot air & inadequate cold air - faulty body design [e_buster]
Jun 27, 2010 (8:43 am)
You missed something....
Unlike HVAC systems of a few years ago these new systems have no shutoff for HOT, >190F, coolant flowing through the heater core. So the radiant heating effects from the heater core will ALWAYS have adverse effects of the efficiency of the A/C to cool the cabin.
Buy and install a manual coolant flow shutoff valve so the HOT coolant can be prevented from HEATING the entire area surrounding the heater core.
Also. Most modern day automatic climate control systems are designed to prevent slight discomfort due to TOO cool airflow to your face and upper body. To that end once the cabin air/atmosphere is cooled to your setpoint or closely nearby the blower speed will be significantly reduced, the reheat/remix vane door will be adjusted to provide more WARMISH airflow. Airflow just barely cool enough to maintain the cabin atmosphere nearby the setpoint.
Many of these systems will even open the windshield and footwell ducts to outlet airflow in order to more widely disperse the cooling airflow to prevent discomfort.
Absent installing the shutoff the highest A/C efficiency can be attained via the MAXIMUM cooling setting and use of the blower speed to regulate the cabin comfort level.
Plus: The Human Comfort equation involves more than the surrounding air temperature, radiant heating, or lack thereof, has as much to do with our comfort level as does the atmosphere surrounding us. These highly slanted windshields, with such DEEP dash TOP surface areas are no help at all. To prevent reflections on the windshield that would interfere with the driver's forward vision these are often in a very dark color shade. Absorbing HIGH heat levels in the HOT sun, moving or stationary.
What is needed is a dash top surface covering that has a fresnel effect, reflective forward but non-reflective otherwise.
#175 of 294 Re: CX7 - blows hot air & inadequate cold air - ADDENDUM [e_buster]
Jun 27, 2010 (8:50 am)
"...HVAC inlet air registered 105F about..."
Are you sure you weren't measuring radiant heating effects along with airflow temperature..?? Or even radiant effect moreso than airflow temperature..??
The inlet airflow itself might well have remained in the 75F range while the radiant effects were the result of the 135F engine compartment.
#176 of 294 Re: CX7 - blows hot air & inadequate cold air - ADDENDUM [wwest]
Jul 07, 2010 (8:10 pm)
29K miles 07' CX-7 GT AWD (still under bumper to bumper warranty)
I live in nyc and we drove to Montreal that's about 6-7 hours away for the fourth of July vacation. The AC stopped working on the return trip to nyc (Monday) about 3 hours into the drive. It just blew hot air and it smelled of burnt plastic/rubber, exactly as described by many others on this thread. (I've read every one of the postings here.)
We stopped using the AC and looked for the nearest Mazda dealer as we were driving down, but they were going to be closing early, and we weren't going to make it before their closing time.
Driving in the heat really sucks arse.. and we stopped for gas with about 150 miles to go. Filled up the tank, and the car wouldn't start. So had to call the NY thruway tow truck, to get it off of the thru-way property to a location where the Mazda roadside Tow truck could pick up the car. (NY Thruway towing fee was about $95, which will be reimbursed by Mazda)
(Also called my insurance GEICO's roadside assistance, but that was going to be more expensive, so went ahead with Mazda's roadside service.)
They took the car to an overnight facility and delivered it to the nearest Mazda dealership in Poughkeepsie, which is 1 1/2 - 2 hrs away from where I live.
Mazda Poughkeepsie ordered parts for the car and they will get them in 4 to 7 days.
They are replacing the AC compressor and the belt. Should they be replacing anything else??
I am now without a car for about a week. They have a loaner car for me at the dealership or their local Enterprise rental, but nothing in nyc.
Called Mazda USA and they said that they would reimburse car rental up to $30 per day, but try finding a car rental at that price in Manhattan.
But they will probably cover the cost of the MetroNorth Rail ticket to pickup the car, so I'll just live without a car until I take the chu-chu train to Poughkeepsie to pickup my repaired car.
I am debating on getting the 30K maintenance done in Poughkeepsie too since it's already going to be at a dealer. They were quoting around $380 for the maintenance. Is that a reasonable price?
I tried to see if Mazda USA or Poughkeepsie dealership would be able to get me a discount for the maintenance, but so far, no good news..
Did anyone else experience their car failing to start far from home like this?
Is there a better way to handle situations like this?
The rep at Mazda USA wasn't rude, but not nice either.. defensive, and trying to give as little as he can, and wouldn't even guarantee the Metronorth ticket reimbursement but said that he'll "most likely" approve it when I filed for reimbursement.. not the kind of customer service I was expecting when it's been a rather stressful day being stranded due to their faulty car.
I guess I am not driving a Lexus or a Benz where I would expect that they would provide better service for situations like this.. who knows.
Now I am wondering if I should get some sort of extended warranty. Any recommendations?
Anyways, it's been helpful to read everyone's post, and I'll update after I get all this sorted out and get the car back. Hopefully my updates will help someone else, as this thread has helped me so far.
#178 of 294 Re: maxda cx7 recall investigation [re0876]
Jul 08, 2010 (10:34 am)
Complaint submitted today. I urge others to do so as well.
#179 of 294 Re: CX7 - blows hot air & inadequate cold air - ADDENDUM [ws46]
by Stever@Edmunds HOST
Jul 08, 2010 (10:42 am)
Bummer about the vacation (guess it helps that you were heading home at that point).
About your 30K maintenance question, the Edmunds Maintenance Guide will tell you what it should cost in various US zip codes.
#180 of 294 Re: CX7 - blows hot air & inadequate cold air - ADDENDUM [steve_]
Jul 08, 2010 (7:14 pm)
Yes, the maintenace at 30K should be much cheaper.. maybe I'll do some of the work myself, or at least shop around a little.
I've filed a complaint to: https://www-odi.nhtsa.dot.gov
just doing my part.